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Teaching veterinary parasitology
veterinary parasitology ELSEVIER
Veterinary Parasitology 54 (1994) 269-281
Teaching veterinary parasitology Anna Verster Department of Veterinary TropicalDiseases, Faculty of VeterinaryScience, Universityof Pretoria, Private Bag X04, Onderstepoort 0110, South Africa
Abstract The history of parasitology and the teaching of veterinary parasitology in South Africa are reviewed briefly. Courses in veterinary parasitology are presented at the faculties of veterinary science at the University of Pretoria and the Medical University of South Africa as well as at the Pretoria Technicon. At the University of Pretoria, the three disciplines of veterinary parasitology, entomology, helminthology and protozoology, are covered in 330 core lectures; from 13 to 40% of the contact time is devoted to practical classes. Teaching veterinary parasitology is both labour intensive and costly, viz. R 1700 (US$ 570) per student per annum. Such costs are justified by the R148.8 million (US$49.6 million) spent every year in South Africa on anthelmintics, ectoparasiticides and vaccines to control parasites. Veterinary parasitology is a dynamic subject and the curriculum must be revised regularly to incorporate new information. Because the parasite faunas are so diverse no single textbook can satisfy the requirements of the various institutions worldwide which teach the subject, with the result that extensive use is made of notes. In Australia and in Europe, ticks and tick-borne diseases are less important than they are in Africa; consequently insufficient space is devoted to them in textbooks to satisfy the requirements of the subject in African countries. Parasite control under extensive and intensive conditions is dealt with adequately at the University of Pretoria, but increasing emphasis will be given to small-scale farming systems, particularly if alternative food animals are to be kept.
Keywords: Teaching
1. Introduction The training o f v e t e r i n a r y students m u s t be considered within certain constraints. Veterinary e d u c a t i o n is very costly a n d it is unlikely that any institution 0304-4017/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0304-4017 ( 94 )03089-F
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would consider increasing the length of time required to complete the course. Each academic year lasts 30 weeks giving a total of only 165 weeks for the whole undergraduate course. It is impossible to include specialist training in any discipline in such a limited period. My colleague, Professor Banie Penzhorn, says that all we can do is "to point their noses in the right direction". A further problem is how to include relevant new information in an overloaded syllabus which is already bursting out of its time frame. During the last five decades all branches of the biological sciences, including parasitology, have experienced an explosion of new information. Between 1960 and 1982 the number of publications in veterinary science doubled while those in parasitology increased 5.3 fold (Barriga, 1983 ). How much of this knowledge is relevant to the student or the practitioner of the 1990s? The veterinary parasitology curriculum already exceeds the time allocated to it and further information, however interesting to the teacher, cannot be added indiscriminately. However, we must also bear in mind that the students of today will still be practising as veterinarians in the year 2020. Will the knowledge they acquire now equip them to carry out their tasks two or even three decades hence? Although some of the knowledge painstakingly acquired a century or more ago may not be used by a veterinarian in the 21 st century, much of it is still relevant today. A brief consideration of the history of parasitology would help in assessing and evaluating the teaching of the subject both now and in the future. (Unless other references are given, the following discussion is largely based on Foster, 1965.) Some knowledge or awareness of parasites goes back to prehistoric times. As man became aware of the parasitic nature and detrimental effects of these organisms, efforts were made to rid the body of them. After Linnaeus introduced the binomial classification, parasites were more accurately described, and their taxonomy was laid on firm foundations by workers such as Pallas, G6ze, Rudolphi and many others. In the 19th century, an exciting period in the history of parasitology followed, when the life cycles of many parasites were elucidated, particularly those of trematodes and cestodes. Application of this knowledge of the life cycles, particularly of the cestodes, resulted in the institution of control measures to break the cycles of some. For example, this knowledge was used to great advantage in Iceland for the control of Echinococcus granulosus (P~ilsson, 1976 ). Unfortunately, control methods are not always as effective and some parasites, e.g. Taenia solium and Taenia saginata, remain serious problems in many parts of the world to this day. In 1674 Van Leeuwenhoek observed ciliates in freshwater and subsequently found organisms, probably Eimeria stiedai, in the bile of a rabbit. The development of parasitic protozoology was slow initially but this changed towards the end of the 19th century, when dramatic discoveries were made. Theobald Smith showed that the bite of an arthropod transmitted a parasitic protozoan and that the parasite could be passed transovarially to the subsequent generation of arthropods. The discovery that Boophilus annulatus transmits Babesia bigemina
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was followed by the identification of the vectors of many protozoal diseases of domestic animals, particularly in Africa (Neitz, 1965). In 1894, while he was working at Ubombo in Zululand, South Africa, David Bruce found that tsetse flies (Glossina spp. ) were the vectors of nagana or trypanosomosis. It was also during this period that pioneering research was conducted on malaria by many workers including Laveran, Manson and Ross. As in helminthology, however, knowledge of the life cycles of the protozoan parasites did not necessarily lead to effective control; many still cause devastating diseases in humans and domestic livestock. During the past few decades significant advances have been made in developing parasiticides but, despite the great promise shown by these substances, parasites and parasitoses remain a problem throughout the world. Many parasites, belonging to all the major groups, exhibit increasing resistance to these chemicals. This increases the urgency for research on alternative control measures. Irradiated larvae of the cattle lungworm, Dictyocaulus viviparus, induced a good immunity in calves and a vaccine has been marketed commercially (Jarrett et al., 1960). Effective vaccines against the larval stages of cestodes have also been developed, but their preparation is self-limiting because developing oncospheres are the source of the antigen (Rickard and Adolph, 1976). An important breakthrough, therefore, was the development of a vaccine against Taenia ovis using recombinant techniques (Johnson et al., 1989 ). Similar vaccines against the larval stages of Taenia saginata and Taenia solium would be a great advance but have yet to be developed. Vaccines against gastro-intestinal nematodes are not yet available. In recent years, particularly since the development of more effective parasiticides, there has been a change in emphasis in the control of parasites. The treatment and cure of the individual host, be it man or an animal, has always been and will continue to be of cardinal importance. At present, however, treatment on a flock or herd basis to raise the production potential of domestic livestock has assumed greater importance. When one considers the developments in parasitology in the last 150 years, and the speed with which new information is becoming available, it is obvious that the veterinary parasitology curriculum must accommodate recent advances. This includes advances in parasitology as well as in related fields such as molecular biology. How can this be accomplished in the time allocated to the subject? Also, due consideration must be given to the type of work in which veterinarians will be involved, not only immediately after they graduate but also 20 or 30 years hence.
2. Parasitology in South Africa
The relevance of parasitology at the end of the 20th century and its importance in Africa are demonstrated by the fact that in the relatively small geographical
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area of the Pretoria-Witwatersrand region there are five institutions which give undergraduate as well as postgraduate courses in general parasitology or in its individual disciplines (Table 1 ). The three disciplines of parasitology, namely protozoology, helminthology and entomology, are a major component of the Bachelor of Veterinary Science (BVSc) III curriculum at the University of Pretoria as all the core lectures are given in this study year. This initial training is augmented and applied when the students work in the clinics and visit farms later in the course. In the fifth year a very brief practical demonstration on the recovery of helminths at post mortem is given to each group of students before they begin their post mortem practicals in pathology. During their final year each clinic group takes part in 3-4 hour discussion classes dealing with such aspects as integrated control in each discipline. At the University of Pretoria, post-graduate courses in veterinary parasitology include a Master of Veterinary Medicine which is a specialist degree comprising the three disciplines. There is also research towards a Master of Science and Doctor of Philosophy in any one of the three disciplines. Capita selecta courses in the subject as a whole or in one of the disciplines are presented when required in Veterinary Public Health, Wildlife Diseases, Large Animal, Small Livestock as well as Small Animal Medicine for the degree MMedVet. The undergraduate courses in Veterinary Parasitology consist of 330-360 lectures ( 172-240 hours ). This may seem to overemphasise the subject but the imTable 1 Courses in parasitology presented at different institutions in the Pretoria-Witwatersrand region Institution
Course
Year of study
Subject
No of
lectures Medical University of South Africa
MB ChB
BVMCh
4th 4th
Parasitology Helminthology Protozoology Vet. entomology
University of Pretoria
MB ChB
Dip Trop Med& Hyg BVSc
3rd Post-Grad 3rd
Parasitology Parasitology Helminthology Protozoology Vet. entomology
University of the Witwatersrand Pretoria Technicon
Johannesburg Technicon
5th 1st 3rd
Dip Vet Nursing MBChB Dip Trop Med& Hyg Dip Vet Tech
Post-Grad 1st
Dip Med Tech Dip Publ Health Dip Med Tech
1st 1st 1st
Parasitology Parasitology Parasitology Parasitology Helminthology Protozoology Vet. entomology
Parasitology Parasitology Parasitology
35 120 120 95 17 10 120 120 90 18 60 52 44 120 120 120 30 96 30
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portance of parasites of livestock in South Africa is shown by the financial costs of controlling both the parasites themselves and the diseases that they cause. In 1991, anthelmintics accounted for 26.5% and ectoparasiticides for 31.2% of the R260.6 million spent on veterinary pharmaceutical products in the RSA (P.T. Oberem, personal communication, 1993 ). In the year 1991 / 1992, the Onderstepoort Veterinary Institute sold 13 125 614 doses of vaccine against protozoal and vector-borne diseases. The monetary value of the pharmaceutical products and vaccines against parasites came to a total of R 148.8 million (US$ 49.6 million ). This figure excludes the costs of coccidiostats, on which R12.6 million was spent in 1989 (Penzhorn, 1990). The control of parasites is equally important and more costly in countries such as the United States where in 1986, the retail sales of antiparasitic drugs totalled US$ 410 million for endo- and US$ 468 million for ecto-parasites (Malone, 1989). In contrast to veterinary science, parasitology receives much less attention in human medicine (Table 1 ). In the MB ChB courses offered by three medical schools, from 17 to 52 lectures are devoted to parasitology. This is a surprisingly low number in view of estimates of the prevalence of parasites in humans (Table 2). In 1946 Stoll estimated the prevalence of helminths in humans and, if only those helminths with a cosmopolitan distribution are considered, almost 2 billion people were infected with worms. More recent estimates by Schmidt and Roberts (1989) and Jeffrey and Leach (1991) are considerably higher. Thus it would appear that a considerable proportion of the world's population is 'wormy'. This surely should warrant more attention from the medical parasitologists. Estimates of the prevalence of malaria are equally dismaying as 2.6 billion people are at risk and 10 million cases occur annually (Heck, 1991 ). Some of the human parasites are zoonoses and therefore fall within in the field of veterinary parasitology. The emphasis placed on veterinary parasitology in South Africa can be traced Table 2 Estimates of the prevalence of some human helminths Helminths
Sehistosoma spp. Diphyllobothrium latum Taenia saginata Taenia solium Ascaris lumbricoides Dracunculus medinensis Hookworms Onchocerca volvulus Filarial worms Strongyloides stercoralis Trichuris trichuria
Number of people infected (millions) Stoll (1947)
Schmidt and Roberts (1989)
Jeffrey and Leach ( 1991 )
114.4 10.4 38.9 2.5 644.4 48.3 456.8 19.8 255.8 34.9 355.1
271 1.26 billion 932
204 16 5 Worldwide 100 900 40 70 600
657 687
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back to the beginning of Veterinary Science in southern Africa. When Arnold Theiler arrived in South Africa in 1891 virtually nothing was known of the diseases, particularly parasitic diseases, of livestock in the country. In 1908, the Veterinary Research Institute was opened at Onderstepoort, and in 1920 Theiler founded the Faculty of Veterinary Science. The Faculty was administered jointly by the Department of Agriculture and the Transvaal University College (later the University of Pretoria) until 1973. At this time, it was taken over by the University. Up to then, lectures were given, on a part-time basis, by research workers at the Veterinary Research Institute. These included eminent parasitologists such as P.J. du Toit, Wilhelm Neitz, Herman M6nnig, Rein Ortlepp, Richard Reinecke and Ivan Horak. Because the lecturers were usually heavily involved in research, much attention was given to the practical aspects of the various subjects. This tradition has continued and from 13 to 40% of the contact time in all three disciplines is devoted to practical classes. At first glance this may seem excessive but a veterinarian must diagnose a parasitic infestation before effective treatment can be applied to either individuals or groups of animals. In a general introduction to veterinary parasitology the students' attention is drawn to the inter-relationships between the disciplines. Protozoology deals with directly transmitted and vector-borne infections and their control. The veterinary entomology lectures are devoted to ticks, mites, insects and their dispersion, role as vectors of disease, and control. In the theoretical component of helminthology, attention is paid to the life cycles, pathogenesis, clinical signs, epidemiology and chemotherapy and the integrated control of the nematodes, trematodes and cestodes that occur in South Africa. From eight to 12 lectures are also devoted to discussion classes in which groups of students are assigned problems to solve. In protozoology the students must find and identify 26 species of protozoa in blood smears and other tissues and in veterinary entomology 18 acarines and 20 insects must be identified to the generic or specific level. In helminthology 48 of the 120 sessions are practicals. Practical classes are labour intensive and the programme of scheduled classes, attendance at which is compulsory, is issued to the students at the beginning of the year. However, the lecturer must be an 'opportunist' and on the look out constantly for additional demonstration material. The practical examination, which is in three parts, is largely 'open book' and accounts for 50% of the final examination mark. Each BVSc III student is issued with a compound and a stereo-microscope as well as a McMaster slide, various pipettes, a counting chamber, etc. In addition, they are given mounted specimens of various helminths, protozoa and arthropods as well as whole specimens of the latter. Each student is issued with more than 150 specimens. In the first practical classes, various helminths and their life cycles are demonstrated to the students as only those with a farming background have any concept of what a 'worm' is. This familiarisation process is augmented by 35 mm slides
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and such films and videos as are available. Both a compound and a stereo-microscope, coupled to video-monitors, are invaluable for demonstrating the morphological features of the helminths. In some instances, such as the demonstration of equid helminths, a multi-medium approach of microscopes coupled to the monitors is used simultaneously with an overhead and a slide projector. The morphological features of helminths are also demonstrated to groups of six students at the multi-head teaching microscope, and they are taught to relate these to the published descriptions. They are not expected to memorise morphological characteristics but must be able to identify the helminths with the aid of published descriptions. The diagnosis of helminths in the live animal is of cardinal importance and students must be familiar with the various methods of examining faeces for helminth eggs. The quantitative methods include the McMaster technique for nematodes and the Pitchford-Visser filters for trematodes. The faecalyser test is used for the qualitative demonstration of nematode eggs in carnivores and other hosts. The students must be familiar with the morphology of helminth eggs and be able to identify those that have a characteristic morphology. The diagnosis of immature conical flukes by sedimentation is also demonstrated. Intestinal tracts of sheep and goats are purchased from an abattoir that sells 'dirty tripe' and the contents of these small intestines are artificially seeded with various species of helminths recovered from donor animals. Each student is issued with 3-4 m of such a seeded intestinal tract and must recover the helminths quantitatively, identify the different species present and describe the composition of the worm burden. The helminths of cattle and horses and those of the large intestine of sheep and goats are issued separately for students to become familiar with their morphology. Dogs and cats, destroyed by an animal welfare society, are also used for practical classes. Their faeces are examined for helminth eggs using the faecalyser method, and their helminths are recovered quantitatively and identified. The sexual stages of trematodes and cestodes of domestic animals, as well as the lesions they and their larval and immature stages cause, are obtained from abattoirs for demonstration to the students. Students must be able to identify the molluscan intermediate hosts of trematodes of domestic livestock and, when they are available, the invertebrate intermediate hosts of cestodes are also demonstrated. The practical examination is conducted in three parts at various times throughout the year. These examinations are largely 'open book'. Certain aspects, which should be common knowledge to a veterinarian (e.g. the larval stages and lesions caused by trematodes and cestodes), account for 20% of the final mark. Students are tested on these aspects in a 'Hit and Run' examination and this is the only part of the practical examination which is not 'open book'. Since ticks and tick-borne diseases are of great importance in South Africa as much time is devoted to them in the practical classes as to the insects. Several of the newer acaricides can be administered as 'pour-ons'. Despite this there are still
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many dip tanks and spray-races in use and it is essential that the future veterinarian is familiar with their construction and management. A demonstration of animals being dipped is of great value, even when there are structural faults or the tank is not well managed. The predilection sites of ticks are demonstrated by releasing different stages of various tick species on calves and allowing them to engorge. These stages are collected by the students who note the place of attachment and identify the species and stage of development. Examination of these calves after the students collect ticks from them shows that veterinary students are as effective as the best acaricides in removing ticks! In one instance, a spin-off from this practical was the demonstration and treatment of sweating sickness in one of the calves. Similarly, spring lamb paralysis may be induced by placing a large number of Rhipicephalus evertsi on a relatively small lamb; the rapid recovery of the animal may also be induced by removal of the ticks. Students collect flies in and around the post-mortem halls and search for maggots and pupae in compost heaps nearby. Wings, spiracles, etc. are mounted on slides for identification. In the training of post-graduate students this practical may be extended to include the identification of the larvae of blowflies and other larvae associated with myiasis, e.g. Cordylobia anthropophaga, by examination of the cephalopharyngeal skeleton. Ectoparasites on free-range chickens are common and numerous. They are a valuable source of practical material and diagnostic experience. The practical components of the courses in veterinary parasitology are labour intensive and costly. For the helminthology practicals, from seven to ten species of nematodes are maintained in pure culture in donor sheep and cattle. When infective material is available, animals are also infected with Fasciola spp., Paramphistomum spp. and Schistosoma mattheei. To meet the needs of the practical classes, 36-38 sheep and one to two oxen are used annually. The cost of the animals, feed, labour and technical assistance is over R106 000 (US$35 333), i.e. more than R1000 (US$353) per student per annum. If the chemicals, specimens and maintenance of the microscopes for the three disciplines in parasitology are included the cost is R 1700 (US$ 570) per student per annum.
3. Comparison of veterinary parasitology courses The basic requirement of an undergraduate course in veterinary parasitology is obviously to train future veterinarians in the subject, but can there be a 'universal' course that successfully fulfils the requirements of a 'universal' veterinarian? In other words, does a veterinarian in a companion animal practice in London require the same training in parasitology as one with a large animal practice in the northern Transvaal bushveld? Undoubtedly their basic requirements would be the same but in each case more specialised knowledge is essential for each to carry out their respective tasks successfully.
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In 1980, a second Faculty of Veterinary Science was established at the Medical University of South Africa at Medunsa. The three disciplines of veterinary parasitology are taught in the fourth year; the number of lectures is similar to that at the University of Pretoria. In helminthology, the practical component of the course accounts for 50% of the contact time. In this course more emphasis is placed on integrated methods rather than on chemotherapy to control helminthosis. Colleagues in Veterinary Schools in Australia, the United Kingdom, the United States, Zimbabwe and South Africa kindly provided syllabuses of the courses presented at their institutions. Unfortunately it is impossible to compare these directly because the time allocated to lectures, practicals or laboratories varied and was not always stipulated. Moreover, besides the core lectures, certain parasites are dealt with in clinics a n d / o r in lectures dealing with various systems. Although a detailed comparison cannot be made, certain differences are apparent and can be related to the importance of particular parasites in given regions. Thus, tick-borne protozoal diseases are of great economic importance in Africa but, with few exceptions, are of mainly academic interest in Australia and Europe. It is therefore to be expected that Veterinary Schools in Glasgow and London devote a mere 13 and 14 lectures respectively to ticks and tick-borne diseases while 69 lectures deal with these subjects at the University of Pretoria. Many of the schools that responded to my request for information stated that they were in the process of revising their curricula. Such revision is an essential component of the teaching of any scientific subject and should be a continuous process, not only to incorporate new information but also to adapt to changes within the parasitic population in an area. Although it has been known for more than 20 years that nematodes may become resistant to anthelmintics, this is no longer of purely academic interest. In South Africa, Haemonchus contortus is the most important helminth of sheep in the summer rainfall region and resistance has been reported to all the major groups of anthelmintics. A similar situation pertains in the case of Boophilus decoloratus, an ixodid tick of cattle. It is therefore inevitable that more attention is devoted to integrated control measures now than in previous years. Companion animals frequently accompany their owners when they visit foreign countries and may thus introduce parasites, including zoonoses, to regions where these did not previously occur. These factors must be considered when reviewing a curriculum.
4. W h a t to teach and h o w to teach it
As more information is added to the already overfull curriculum, training in veterinary parasitology must become more student orientated. Formal lectures traditionally form the core of all tertiary teaching, and their importance and validity cannot be questioned, but they should be complemented by self-study and should not dominate the course. Greater emphasis should be placed on the stu-
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dent's ability to retrieve and apply information when making a diagnosis and solving a problem. Such changes, however, do not take place overnight and both the students and the lecturers must adapt and learn new skills. Of necessity, student evaluation will alter, with examinations and tests on the higher cognizance levels and greater use will be made of 'open book' evaluation. Barriga (1983 ) points out and illustrates that multiple choice questions can be adapted to become more meaningful. At the University of Pretoria we make use of multiple choice questions in tests, but they may not constitute more than 20% of the overall test marks. As a result of the limitations imposed by the available time new information cannot, and must not, be added to the syllabus indiscriminately. Barriga ( 1983 ) is correct in stating that "understanding suitable concepts is more permanent than the memorisation of multiple facts". While I am wholly in agreement with these sentiments such changes must be undertaken with great care and circumspection so that veterinary parasitology is not downgraded, as has happened in medical parasitology. Students generally find the life cycles of parasites confusing and we could simplify them to a conceptual basis. There are, however, certain essential facts that a veterinarian must know without reference to a textbook. This is well illustrated by the life cycles of the Ascarididae. The pathogenesis and clinical signs ofAscaris suum infections closely follow the tracheal migration of the parasite in the pig, and this assists with the rapid diagnosis of the condition. Similarly, knowledge of the somatic migration and transplacental transmission of Toxocara canis are essential for the rapid diagnosis and treatment of the infection in puppies. With the advent of broad spectrum anthelmintics, acaricides and insecticides the precise identity of individual parasites has, with some exceptions, become less important. Nevertheless, a parasite such as Dirofilaria immitis must be treated with specific drugs and its microfilariae correctly identified. And, although the morphology and taxonomy of helminths and ectoparasites is of less consequence than it was previously, that of the parasitic protozoa, which cannot be treated with broad spectrum drugs, remains absolutely essential. Another factor to be considered is the field of activity of the veterinarian and how this has changed in the past few decades. Barriga (1983) reports that in the United States the number of veterinarians specialising in small animals increased from 20% in 1964 to more than 35% in 1983 but, during the same period, those in mixed practices decreased from 43% to 32%. The number of veterinarians in large animal practices, public health and other activities showed only slight changes. There are no statistics on changes in the activities of veterinarians in South Africa. In 1986/1987 however, 27% of the practices devoted all their time to small animals, 3% concentrated on cattle and less than 1% on small livestock (H.M. Terblanche, personal communication, 1993). Such trends ought to be reflected in the curriculum but this is not always feasible. Although few practices specialize in small livestock, these animals are major food species and, as they are highly susceptible to helminth infections, considerable time is devoted to the control of these parasites. Similarly, protozoal diseases cause great losses in cattle and, as already stated, much time is devoted to their control.
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Throughout its history the teaching of veterinary parasitology has been hampered by a lack of suitable textbooks in all three disciplines and, although Africa is well-endowed with parasites, it is still 'Darkest Africa' to most of the authors of textbooks. In 1934, the first of several editions of 'Veterinary Helminthology and Entomology' by Herman Mrnnig appeared. Professor Lord Soulsby ( 1982 ) revised the last two editions, and has expanded it to include the parasitic protozoa, but unfortunately sufficient attention has still not been given to the parasites and conditions that occur in Africa. Reinecke ( 1983 ) concentrates on helminths in the southern hemisphere but the information he gives is too detailed for undergraduates. An excellent textbook on entomology by Kettle (1984) deals in depth with Boophilus annulatus and Rhipicephalus appendiculatusbut other ticks that are vectors of important diseases in Africa receive cursory treatment. Howell et al. (1978) produced a well-illustrated bulletin on the arthropod parasites of livestock in South Africa, but this now requires updating. To compensate for such shortcomings, Urquhart et al. ( 1987 ) wrote a textbook to meet the requirements of the course taught at the University of Glasgow. It is thus clear that there cannot be a universal textbook on the subject to satisfy the needs of the courses in veterinary parasitology presented at different institutions on the different continents and in different geographical regions. This is evident from the extensive notes that have to be provided to the students at the University of Pretoria for protozoology and veterinary entomology; the textbook by Reinecke ( 1983 ) is used in helminthology but it is augmented with notes. Extensive notes are also provided to the students at Medunsa (J.D.F. Boomker, personal communication, 1992), the University of Melbourne (I. Beveridge, personal communication, 1992 ) and Murdoch University (R.C.A. Thompson, personal communication, 1992).
5. Conclusion
I hear and I forget I see and I remember I do and I understand It behoves all teachers in veterinary science to bear the above quotation in mind when drawing up the curriculum of a subject. This is particularly true in veterinary parasitology which is a dynamic subject with exciting new discoveries being made at a startling pace. Seeing and doing certain procedures facilitates the understanding and learning of basic concepts. In veterinary parasitology 'hands on' training and information retrieval should be maximised rather than the mere memorising of facts. The teacher must also guard against the temptation to teach the students all the detailed information acquired after a lifetime of dedicated study. Such detail camouflages the basic concepts and only serves to confuse the student. Africa has a rich diversity of parasites and, especially in view of the resistance problems that have developed against parasiticides, new measures to control them
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must be developed. To date, attention focused mainly on the control of parasites in livestock under extensive and intensive conditions. As drought and famine increase in many parts of Africa, more attention should be devoted to increasing food production at the subsistence farming level. Such farming need not be limited to domestic livestock but can also include alternative food animals such as the cane rat, Thryonomysswinderianus, or the giant rat, Cricetomysgambianus. Undoubtedly the greatest advantage of this Faculty, and particularly of the three disciplines in veterinary parasitology, is the fact that it is cheek by jowl with the Onderstepoort Veterinary Institute. In the 70 years since the establishment of the Faculty of Veterinary Science the symbiotic tradition of co-operation that has developed between these two institutions contributes materially to the thorough grounding the students receive in veterinary parasitology.
Acknowledgements Many colleagues very generously provided me with study guides and other information on the courses they teach; they include Professors I. Beveridge, J. Boomker, R.C. Chhabra, J. Duncan, P. Fripp, M. Issacson, D. Jacobs, A. Lewis, B.E. Matthews, M. Sewell, C. Short, R.J. Thomas, R.C.A. Thompson and Dr P. Sauer. I am also most grateful to Dr Jane Walker, Professor I.G. Horak, Professor R. Connor and Professor R.C. Krecek for their assistance with the manuscript.
References Barriga, O.O., 1983. Teaching veterinary parasitology for the XXI Century. J. Vet. Med. Educ., 10: 35-40. Foster, W.D., 1965. A History of Parasitology. Livingstone, Edinburgh. Heck, J.E., 1991. Malaria. Primary care. Clin. Off. Pract., (Parasite Dis.), 18:195-21 I. Howell, C.J., Walker, J.B. and Nevill, E.M., 1978. Ticks, mites and insects infesting domestic animals in South Africa. Part 1. Descriptions and biology. Sci. Bull. No. 393, Department of Agricultural Technical Services, Republic of South Africa, 69 pp. Jarrett, W.F.H., Jennings, R.W., McIntyre, W.I.M., Mulligan, W. and Urquhart, G.M., 1960. Immunological studies on Dictyocaulus viviparus infection. Immunity produced by administration of irradiated larvae. Immunology, 3:145-157. Jeffrey, H.C. and Leach R.M., 1991. Atlas of Medical Helminthology and Protozoology, 3rd edn. Revised by G.O. Cowan. Churchill Livingston, Edinburgh. Johnson, K.S., Harrison, G.B.L., Lightowlers, M.W., O'Hoy, K.L., Cougle, W.W., Dempster, R.P., Lawrence, S.B., Vinton, J.G., Heath, D.D. and Rickard, M.D., 1989. Vaccination against ovine cysticercosis using a defined recombinant antigen. Nature, 338: 585-587. Kettle, D.S., 1984. Medical and Veterinary Entomology. Croom Helm, London. Malone, J.B., 1989. Texas fever, two-headed calves and the Hatch Act--100 years and counting for veterinary parasitology in the United States. Vet. Parasitol., 33: 3-29. M~Snnig,H.O., 1934. Veterinary Helminthology and Entomology. Bailliere Tindall & Cox, London. Neitz, W.O., 1965. A checklist and hostlist of the zoonoses occurring in mammals and birds in South and South West Africa. Onderstepoort J. Vet. Res., 32: 189-374. P~ilsson, P.A., 1976. Echinococcosis and its elimination in Iceland. Hist. Med. Vet., 1: 4-10.
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Penzhorn, B.L., 1990. Parasitologie: 'n Raakvlak tussen veeartsenykunde en dierkunde. Publikasis van die Universiteit van Pretoria, Nuwe Reeks Nr., 271: 2-14. Reinecke, R.K., 1983. Veterinary Helminthology. Butterworths, Durban. Rickard, M.D. and Adolph, A.J., 1976. Vaccination of calves against Taenia saginata infection using a 'parasite-free' vaccine. Vet. Parasitol., 1: 389-390. Schmidt, G.D. and Roberts, L.S., 1989. Foundations of Parasitology, 4th edn. Times Mirror Mashy College Publishing, St Louis. Soulsby, E.J.L., 1982. Helminths, Arthropods and Protozoa of Domesticated Animals, 7th edn. Bailliere Tindall, London. Stoll, N.R., 1947. This wormy world. J. Parasitol., 33: 1-18. Urquhart, G.M., Armour, J., Duncan, J.L., Dunn, A.M. and Jennings, F.W., 1987. Veterinary Parasitology. Longman Scientific & Technical, Harlow, UK.
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Teaching veterinary parasitology Anna Verster Department of Veterinary TropicalDiseases, Faculty of VeterinaryScience, Universityof Pretoria, Private Bag X04, Onderstepoort 0110, South Africa
Abstract The history of parasitology and the teaching of veterinary parasitology in South Africa are reviewed briefly. Courses in veterinary parasitology are presented at the faculties of veterinary science at the University of Pretoria and the Medical University of South Africa as well as at the Pretoria Technicon. At the University of Pretoria, the three disciplines of veterinary parasitology, entomology, helminthology and protozoology, are covered in 330 core lectures; from 13 to 40% of the contact time is devoted to practical classes. Teaching veterinary parasitology is both labour intensive and costly, viz. R 1700 (US$ 570) per student per annum. Such costs are justified by the R148.8 million (US$49.6 million) spent every year in South Africa on anthelmintics, ectoparasiticides and vaccines to control parasites. Veterinary parasitology is a dynamic subject and the curriculum must be revised regularly to incorporate new information. Because the parasite faunas are so diverse no single textbook can satisfy the requirements of the various institutions worldwide which teach the subject, with the result that extensive use is made of notes. In Australia and in Europe, ticks and tick-borne diseases are less important than they are in Africa; consequently insufficient space is devoted to them in textbooks to satisfy the requirements of the subject in African countries. Parasite control under extensive and intensive conditions is dealt with adequately at the University of Pretoria, but increasing emphasis will be given to small-scale farming systems, particularly if alternative food animals are to be kept.
Keywords: Teaching
1. Introduction The training o f v e t e r i n a r y students m u s t be considered within certain constraints. Veterinary e d u c a t i o n is very costly a n d it is unlikely that any institution 0304-4017/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0304-4017 ( 94 )03089-F
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would consider increasing the length of time required to complete the course. Each academic year lasts 30 weeks giving a total of only 165 weeks for the whole undergraduate course. It is impossible to include specialist training in any discipline in such a limited period. My colleague, Professor Banie Penzhorn, says that all we can do is "to point their noses in the right direction". A further problem is how to include relevant new information in an overloaded syllabus which is already bursting out of its time frame. During the last five decades all branches of the biological sciences, including parasitology, have experienced an explosion of new information. Between 1960 and 1982 the number of publications in veterinary science doubled while those in parasitology increased 5.3 fold (Barriga, 1983 ). How much of this knowledge is relevant to the student or the practitioner of the 1990s? The veterinary parasitology curriculum already exceeds the time allocated to it and further information, however interesting to the teacher, cannot be added indiscriminately. However, we must also bear in mind that the students of today will still be practising as veterinarians in the year 2020. Will the knowledge they acquire now equip them to carry out their tasks two or even three decades hence? Although some of the knowledge painstakingly acquired a century or more ago may not be used by a veterinarian in the 21 st century, much of it is still relevant today. A brief consideration of the history of parasitology would help in assessing and evaluating the teaching of the subject both now and in the future. (Unless other references are given, the following discussion is largely based on Foster, 1965.) Some knowledge or awareness of parasites goes back to prehistoric times. As man became aware of the parasitic nature and detrimental effects of these organisms, efforts were made to rid the body of them. After Linnaeus introduced the binomial classification, parasites were more accurately described, and their taxonomy was laid on firm foundations by workers such as Pallas, G6ze, Rudolphi and many others. In the 19th century, an exciting period in the history of parasitology followed, when the life cycles of many parasites were elucidated, particularly those of trematodes and cestodes. Application of this knowledge of the life cycles, particularly of the cestodes, resulted in the institution of control measures to break the cycles of some. For example, this knowledge was used to great advantage in Iceland for the control of Echinococcus granulosus (P~ilsson, 1976 ). Unfortunately, control methods are not always as effective and some parasites, e.g. Taenia solium and Taenia saginata, remain serious problems in many parts of the world to this day. In 1674 Van Leeuwenhoek observed ciliates in freshwater and subsequently found organisms, probably Eimeria stiedai, in the bile of a rabbit. The development of parasitic protozoology was slow initially but this changed towards the end of the 19th century, when dramatic discoveries were made. Theobald Smith showed that the bite of an arthropod transmitted a parasitic protozoan and that the parasite could be passed transovarially to the subsequent generation of arthropods. The discovery that Boophilus annulatus transmits Babesia bigemina
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was followed by the identification of the vectors of many protozoal diseases of domestic animals, particularly in Africa (Neitz, 1965). In 1894, while he was working at Ubombo in Zululand, South Africa, David Bruce found that tsetse flies (Glossina spp. ) were the vectors of nagana or trypanosomosis. It was also during this period that pioneering research was conducted on malaria by many workers including Laveran, Manson and Ross. As in helminthology, however, knowledge of the life cycles of the protozoan parasites did not necessarily lead to effective control; many still cause devastating diseases in humans and domestic livestock. During the past few decades significant advances have been made in developing parasiticides but, despite the great promise shown by these substances, parasites and parasitoses remain a problem throughout the world. Many parasites, belonging to all the major groups, exhibit increasing resistance to these chemicals. This increases the urgency for research on alternative control measures. Irradiated larvae of the cattle lungworm, Dictyocaulus viviparus, induced a good immunity in calves and a vaccine has been marketed commercially (Jarrett et al., 1960). Effective vaccines against the larval stages of cestodes have also been developed, but their preparation is self-limiting because developing oncospheres are the source of the antigen (Rickard and Adolph, 1976). An important breakthrough, therefore, was the development of a vaccine against Taenia ovis using recombinant techniques (Johnson et al., 1989 ). Similar vaccines against the larval stages of Taenia saginata and Taenia solium would be a great advance but have yet to be developed. Vaccines against gastro-intestinal nematodes are not yet available. In recent years, particularly since the development of more effective parasiticides, there has been a change in emphasis in the control of parasites. The treatment and cure of the individual host, be it man or an animal, has always been and will continue to be of cardinal importance. At present, however, treatment on a flock or herd basis to raise the production potential of domestic livestock has assumed greater importance. When one considers the developments in parasitology in the last 150 years, and the speed with which new information is becoming available, it is obvious that the veterinary parasitology curriculum must accommodate recent advances. This includes advances in parasitology as well as in related fields such as molecular biology. How can this be accomplished in the time allocated to the subject? Also, due consideration must be given to the type of work in which veterinarians will be involved, not only immediately after they graduate but also 20 or 30 years hence.
2. Parasitology in South Africa
The relevance of parasitology at the end of the 20th century and its importance in Africa are demonstrated by the fact that in the relatively small geographical
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area of the Pretoria-Witwatersrand region there are five institutions which give undergraduate as well as postgraduate courses in general parasitology or in its individual disciplines (Table 1 ). The three disciplines of parasitology, namely protozoology, helminthology and entomology, are a major component of the Bachelor of Veterinary Science (BVSc) III curriculum at the University of Pretoria as all the core lectures are given in this study year. This initial training is augmented and applied when the students work in the clinics and visit farms later in the course. In the fifth year a very brief practical demonstration on the recovery of helminths at post mortem is given to each group of students before they begin their post mortem practicals in pathology. During their final year each clinic group takes part in 3-4 hour discussion classes dealing with such aspects as integrated control in each discipline. At the University of Pretoria, post-graduate courses in veterinary parasitology include a Master of Veterinary Medicine which is a specialist degree comprising the three disciplines. There is also research towards a Master of Science and Doctor of Philosophy in any one of the three disciplines. Capita selecta courses in the subject as a whole or in one of the disciplines are presented when required in Veterinary Public Health, Wildlife Diseases, Large Animal, Small Livestock as well as Small Animal Medicine for the degree MMedVet. The undergraduate courses in Veterinary Parasitology consist of 330-360 lectures ( 172-240 hours ). This may seem to overemphasise the subject but the imTable 1 Courses in parasitology presented at different institutions in the Pretoria-Witwatersrand region Institution
Course
Year of study
Subject
No of
lectures Medical University of South Africa
MB ChB
BVMCh
4th 4th
Parasitology Helminthology Protozoology Vet. entomology
University of Pretoria
MB ChB
Dip Trop Med& Hyg BVSc
3rd Post-Grad 3rd
Parasitology Parasitology Helminthology Protozoology Vet. entomology
University of the Witwatersrand Pretoria Technicon
Johannesburg Technicon
5th 1st 3rd
Dip Vet Nursing MBChB Dip Trop Med& Hyg Dip Vet Tech
Post-Grad 1st
Dip Med Tech Dip Publ Health Dip Med Tech
1st 1st 1st
Parasitology Parasitology Parasitology Parasitology Helminthology Protozoology Vet. entomology
Parasitology Parasitology Parasitology
35 120 120 95 17 10 120 120 90 18 60 52 44 120 120 120 30 96 30
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273
portance of parasites of livestock in South Africa is shown by the financial costs of controlling both the parasites themselves and the diseases that they cause. In 1991, anthelmintics accounted for 26.5% and ectoparasiticides for 31.2% of the R260.6 million spent on veterinary pharmaceutical products in the RSA (P.T. Oberem, personal communication, 1993 ). In the year 1991 / 1992, the Onderstepoort Veterinary Institute sold 13 125 614 doses of vaccine against protozoal and vector-borne diseases. The monetary value of the pharmaceutical products and vaccines against parasites came to a total of R 148.8 million (US$ 49.6 million ). This figure excludes the costs of coccidiostats, on which R12.6 million was spent in 1989 (Penzhorn, 1990). The control of parasites is equally important and more costly in countries such as the United States where in 1986, the retail sales of antiparasitic drugs totalled US$ 410 million for endo- and US$ 468 million for ecto-parasites (Malone, 1989). In contrast to veterinary science, parasitology receives much less attention in human medicine (Table 1 ). In the MB ChB courses offered by three medical schools, from 17 to 52 lectures are devoted to parasitology. This is a surprisingly low number in view of estimates of the prevalence of parasites in humans (Table 2). In 1946 Stoll estimated the prevalence of helminths in humans and, if only those helminths with a cosmopolitan distribution are considered, almost 2 billion people were infected with worms. More recent estimates by Schmidt and Roberts (1989) and Jeffrey and Leach (1991) are considerably higher. Thus it would appear that a considerable proportion of the world's population is 'wormy'. This surely should warrant more attention from the medical parasitologists. Estimates of the prevalence of malaria are equally dismaying as 2.6 billion people are at risk and 10 million cases occur annually (Heck, 1991 ). Some of the human parasites are zoonoses and therefore fall within in the field of veterinary parasitology. The emphasis placed on veterinary parasitology in South Africa can be traced Table 2 Estimates of the prevalence of some human helminths Helminths
Sehistosoma spp. Diphyllobothrium latum Taenia saginata Taenia solium Ascaris lumbricoides Dracunculus medinensis Hookworms Onchocerca volvulus Filarial worms Strongyloides stercoralis Trichuris trichuria
Number of people infected (millions) Stoll (1947)
Schmidt and Roberts (1989)
Jeffrey and Leach ( 1991 )
114.4 10.4 38.9 2.5 644.4 48.3 456.8 19.8 255.8 34.9 355.1
271 1.26 billion 932
204 16 5 Worldwide 100 900 40 70 600
657 687
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back to the beginning of Veterinary Science in southern Africa. When Arnold Theiler arrived in South Africa in 1891 virtually nothing was known of the diseases, particularly parasitic diseases, of livestock in the country. In 1908, the Veterinary Research Institute was opened at Onderstepoort, and in 1920 Theiler founded the Faculty of Veterinary Science. The Faculty was administered jointly by the Department of Agriculture and the Transvaal University College (later the University of Pretoria) until 1973. At this time, it was taken over by the University. Up to then, lectures were given, on a part-time basis, by research workers at the Veterinary Research Institute. These included eminent parasitologists such as P.J. du Toit, Wilhelm Neitz, Herman M6nnig, Rein Ortlepp, Richard Reinecke and Ivan Horak. Because the lecturers were usually heavily involved in research, much attention was given to the practical aspects of the various subjects. This tradition has continued and from 13 to 40% of the contact time in all three disciplines is devoted to practical classes. At first glance this may seem excessive but a veterinarian must diagnose a parasitic infestation before effective treatment can be applied to either individuals or groups of animals. In a general introduction to veterinary parasitology the students' attention is drawn to the inter-relationships between the disciplines. Protozoology deals with directly transmitted and vector-borne infections and their control. The veterinary entomology lectures are devoted to ticks, mites, insects and their dispersion, role as vectors of disease, and control. In the theoretical component of helminthology, attention is paid to the life cycles, pathogenesis, clinical signs, epidemiology and chemotherapy and the integrated control of the nematodes, trematodes and cestodes that occur in South Africa. From eight to 12 lectures are also devoted to discussion classes in which groups of students are assigned problems to solve. In protozoology the students must find and identify 26 species of protozoa in blood smears and other tissues and in veterinary entomology 18 acarines and 20 insects must be identified to the generic or specific level. In helminthology 48 of the 120 sessions are practicals. Practical classes are labour intensive and the programme of scheduled classes, attendance at which is compulsory, is issued to the students at the beginning of the year. However, the lecturer must be an 'opportunist' and on the look out constantly for additional demonstration material. The practical examination, which is in three parts, is largely 'open book' and accounts for 50% of the final examination mark. Each BVSc III student is issued with a compound and a stereo-microscope as well as a McMaster slide, various pipettes, a counting chamber, etc. In addition, they are given mounted specimens of various helminths, protozoa and arthropods as well as whole specimens of the latter. Each student is issued with more than 150 specimens. In the first practical classes, various helminths and their life cycles are demonstrated to the students as only those with a farming background have any concept of what a 'worm' is. This familiarisation process is augmented by 35 mm slides
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and such films and videos as are available. Both a compound and a stereo-microscope, coupled to video-monitors, are invaluable for demonstrating the morphological features of the helminths. In some instances, such as the demonstration of equid helminths, a multi-medium approach of microscopes coupled to the monitors is used simultaneously with an overhead and a slide projector. The morphological features of helminths are also demonstrated to groups of six students at the multi-head teaching microscope, and they are taught to relate these to the published descriptions. They are not expected to memorise morphological characteristics but must be able to identify the helminths with the aid of published descriptions. The diagnosis of helminths in the live animal is of cardinal importance and students must be familiar with the various methods of examining faeces for helminth eggs. The quantitative methods include the McMaster technique for nematodes and the Pitchford-Visser filters for trematodes. The faecalyser test is used for the qualitative demonstration of nematode eggs in carnivores and other hosts. The students must be familiar with the morphology of helminth eggs and be able to identify those that have a characteristic morphology. The diagnosis of immature conical flukes by sedimentation is also demonstrated. Intestinal tracts of sheep and goats are purchased from an abattoir that sells 'dirty tripe' and the contents of these small intestines are artificially seeded with various species of helminths recovered from donor animals. Each student is issued with 3-4 m of such a seeded intestinal tract and must recover the helminths quantitatively, identify the different species present and describe the composition of the worm burden. The helminths of cattle and horses and those of the large intestine of sheep and goats are issued separately for students to become familiar with their morphology. Dogs and cats, destroyed by an animal welfare society, are also used for practical classes. Their faeces are examined for helminth eggs using the faecalyser method, and their helminths are recovered quantitatively and identified. The sexual stages of trematodes and cestodes of domestic animals, as well as the lesions they and their larval and immature stages cause, are obtained from abattoirs for demonstration to the students. Students must be able to identify the molluscan intermediate hosts of trematodes of domestic livestock and, when they are available, the invertebrate intermediate hosts of cestodes are also demonstrated. The practical examination is conducted in three parts at various times throughout the year. These examinations are largely 'open book'. Certain aspects, which should be common knowledge to a veterinarian (e.g. the larval stages and lesions caused by trematodes and cestodes), account for 20% of the final mark. Students are tested on these aspects in a 'Hit and Run' examination and this is the only part of the practical examination which is not 'open book'. Since ticks and tick-borne diseases are of great importance in South Africa as much time is devoted to them in the practical classes as to the insects. Several of the newer acaricides can be administered as 'pour-ons'. Despite this there are still
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many dip tanks and spray-races in use and it is essential that the future veterinarian is familiar with their construction and management. A demonstration of animals being dipped is of great value, even when there are structural faults or the tank is not well managed. The predilection sites of ticks are demonstrated by releasing different stages of various tick species on calves and allowing them to engorge. These stages are collected by the students who note the place of attachment and identify the species and stage of development. Examination of these calves after the students collect ticks from them shows that veterinary students are as effective as the best acaricides in removing ticks! In one instance, a spin-off from this practical was the demonstration and treatment of sweating sickness in one of the calves. Similarly, spring lamb paralysis may be induced by placing a large number of Rhipicephalus evertsi on a relatively small lamb; the rapid recovery of the animal may also be induced by removal of the ticks. Students collect flies in and around the post-mortem halls and search for maggots and pupae in compost heaps nearby. Wings, spiracles, etc. are mounted on slides for identification. In the training of post-graduate students this practical may be extended to include the identification of the larvae of blowflies and other larvae associated with myiasis, e.g. Cordylobia anthropophaga, by examination of the cephalopharyngeal skeleton. Ectoparasites on free-range chickens are common and numerous. They are a valuable source of practical material and diagnostic experience. The practical components of the courses in veterinary parasitology are labour intensive and costly. For the helminthology practicals, from seven to ten species of nematodes are maintained in pure culture in donor sheep and cattle. When infective material is available, animals are also infected with Fasciola spp., Paramphistomum spp. and Schistosoma mattheei. To meet the needs of the practical classes, 36-38 sheep and one to two oxen are used annually. The cost of the animals, feed, labour and technical assistance is over R106 000 (US$35 333), i.e. more than R1000 (US$353) per student per annum. If the chemicals, specimens and maintenance of the microscopes for the three disciplines in parasitology are included the cost is R 1700 (US$ 570) per student per annum.
3. Comparison of veterinary parasitology courses The basic requirement of an undergraduate course in veterinary parasitology is obviously to train future veterinarians in the subject, but can there be a 'universal' course that successfully fulfils the requirements of a 'universal' veterinarian? In other words, does a veterinarian in a companion animal practice in London require the same training in parasitology as one with a large animal practice in the northern Transvaal bushveld? Undoubtedly their basic requirements would be the same but in each case more specialised knowledge is essential for each to carry out their respective tasks successfully.
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In 1980, a second Faculty of Veterinary Science was established at the Medical University of South Africa at Medunsa. The three disciplines of veterinary parasitology are taught in the fourth year; the number of lectures is similar to that at the University of Pretoria. In helminthology, the practical component of the course accounts for 50% of the contact time. In this course more emphasis is placed on integrated methods rather than on chemotherapy to control helminthosis. Colleagues in Veterinary Schools in Australia, the United Kingdom, the United States, Zimbabwe and South Africa kindly provided syllabuses of the courses presented at their institutions. Unfortunately it is impossible to compare these directly because the time allocated to lectures, practicals or laboratories varied and was not always stipulated. Moreover, besides the core lectures, certain parasites are dealt with in clinics a n d / o r in lectures dealing with various systems. Although a detailed comparison cannot be made, certain differences are apparent and can be related to the importance of particular parasites in given regions. Thus, tick-borne protozoal diseases are of great economic importance in Africa but, with few exceptions, are of mainly academic interest in Australia and Europe. It is therefore to be expected that Veterinary Schools in Glasgow and London devote a mere 13 and 14 lectures respectively to ticks and tick-borne diseases while 69 lectures deal with these subjects at the University of Pretoria. Many of the schools that responded to my request for information stated that they were in the process of revising their curricula. Such revision is an essential component of the teaching of any scientific subject and should be a continuous process, not only to incorporate new information but also to adapt to changes within the parasitic population in an area. Although it has been known for more than 20 years that nematodes may become resistant to anthelmintics, this is no longer of purely academic interest. In South Africa, Haemonchus contortus is the most important helminth of sheep in the summer rainfall region and resistance has been reported to all the major groups of anthelmintics. A similar situation pertains in the case of Boophilus decoloratus, an ixodid tick of cattle. It is therefore inevitable that more attention is devoted to integrated control measures now than in previous years. Companion animals frequently accompany their owners when they visit foreign countries and may thus introduce parasites, including zoonoses, to regions where these did not previously occur. These factors must be considered when reviewing a curriculum.
4. W h a t to teach and h o w to teach it
As more information is added to the already overfull curriculum, training in veterinary parasitology must become more student orientated. Formal lectures traditionally form the core of all tertiary teaching, and their importance and validity cannot be questioned, but they should be complemented by self-study and should not dominate the course. Greater emphasis should be placed on the stu-
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dent's ability to retrieve and apply information when making a diagnosis and solving a problem. Such changes, however, do not take place overnight and both the students and the lecturers must adapt and learn new skills. Of necessity, student evaluation will alter, with examinations and tests on the higher cognizance levels and greater use will be made of 'open book' evaluation. Barriga (1983 ) points out and illustrates that multiple choice questions can be adapted to become more meaningful. At the University of Pretoria we make use of multiple choice questions in tests, but they may not constitute more than 20% of the overall test marks. As a result of the limitations imposed by the available time new information cannot, and must not, be added to the syllabus indiscriminately. Barriga ( 1983 ) is correct in stating that "understanding suitable concepts is more permanent than the memorisation of multiple facts". While I am wholly in agreement with these sentiments such changes must be undertaken with great care and circumspection so that veterinary parasitology is not downgraded, as has happened in medical parasitology. Students generally find the life cycles of parasites confusing and we could simplify them to a conceptual basis. There are, however, certain essential facts that a veterinarian must know without reference to a textbook. This is well illustrated by the life cycles of the Ascarididae. The pathogenesis and clinical signs ofAscaris suum infections closely follow the tracheal migration of the parasite in the pig, and this assists with the rapid diagnosis of the condition. Similarly, knowledge of the somatic migration and transplacental transmission of Toxocara canis are essential for the rapid diagnosis and treatment of the infection in puppies. With the advent of broad spectrum anthelmintics, acaricides and insecticides the precise identity of individual parasites has, with some exceptions, become less important. Nevertheless, a parasite such as Dirofilaria immitis must be treated with specific drugs and its microfilariae correctly identified. And, although the morphology and taxonomy of helminths and ectoparasites is of less consequence than it was previously, that of the parasitic protozoa, which cannot be treated with broad spectrum drugs, remains absolutely essential. Another factor to be considered is the field of activity of the veterinarian and how this has changed in the past few decades. Barriga (1983) reports that in the United States the number of veterinarians specialising in small animals increased from 20% in 1964 to more than 35% in 1983 but, during the same period, those in mixed practices decreased from 43% to 32%. The number of veterinarians in large animal practices, public health and other activities showed only slight changes. There are no statistics on changes in the activities of veterinarians in South Africa. In 1986/1987 however, 27% of the practices devoted all their time to small animals, 3% concentrated on cattle and less than 1% on small livestock (H.M. Terblanche, personal communication, 1993). Such trends ought to be reflected in the curriculum but this is not always feasible. Although few practices specialize in small livestock, these animals are major food species and, as they are highly susceptible to helminth infections, considerable time is devoted to the control of these parasites. Similarly, protozoal diseases cause great losses in cattle and, as already stated, much time is devoted to their control.
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Throughout its history the teaching of veterinary parasitology has been hampered by a lack of suitable textbooks in all three disciplines and, although Africa is well-endowed with parasites, it is still 'Darkest Africa' to most of the authors of textbooks. In 1934, the first of several editions of 'Veterinary Helminthology and Entomology' by Herman Mrnnig appeared. Professor Lord Soulsby ( 1982 ) revised the last two editions, and has expanded it to include the parasitic protozoa, but unfortunately sufficient attention has still not been given to the parasites and conditions that occur in Africa. Reinecke ( 1983 ) concentrates on helminths in the southern hemisphere but the information he gives is too detailed for undergraduates. An excellent textbook on entomology by Kettle (1984) deals in depth with Boophilus annulatus and Rhipicephalus appendiculatusbut other ticks that are vectors of important diseases in Africa receive cursory treatment. Howell et al. (1978) produced a well-illustrated bulletin on the arthropod parasites of livestock in South Africa, but this now requires updating. To compensate for such shortcomings, Urquhart et al. ( 1987 ) wrote a textbook to meet the requirements of the course taught at the University of Glasgow. It is thus clear that there cannot be a universal textbook on the subject to satisfy the needs of the courses in veterinary parasitology presented at different institutions on the different continents and in different geographical regions. This is evident from the extensive notes that have to be provided to the students at the University of Pretoria for protozoology and veterinary entomology; the textbook by Reinecke ( 1983 ) is used in helminthology but it is augmented with notes. Extensive notes are also provided to the students at Medunsa (J.D.F. Boomker, personal communication, 1992), the University of Melbourne (I. Beveridge, personal communication, 1992 ) and Murdoch University (R.C.A. Thompson, personal communication, 1992).
5. Conclusion
I hear and I forget I see and I remember I do and I understand It behoves all teachers in veterinary science to bear the above quotation in mind when drawing up the curriculum of a subject. This is particularly true in veterinary parasitology which is a dynamic subject with exciting new discoveries being made at a startling pace. Seeing and doing certain procedures facilitates the understanding and learning of basic concepts. In veterinary parasitology 'hands on' training and information retrieval should be maximised rather than the mere memorising of facts. The teacher must also guard against the temptation to teach the students all the detailed information acquired after a lifetime of dedicated study. Such detail camouflages the basic concepts and only serves to confuse the student. Africa has a rich diversity of parasites and, especially in view of the resistance problems that have developed against parasiticides, new measures to control them
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must be developed. To date, attention focused mainly on the control of parasites in livestock under extensive and intensive conditions. As drought and famine increase in many parts of Africa, more attention should be devoted to increasing food production at the subsistence farming level. Such farming need not be limited to domestic livestock but can also include alternative food animals such as the cane rat, Thryonomysswinderianus, or the giant rat, Cricetomysgambianus. Undoubtedly the greatest advantage of this Faculty, and particularly of the three disciplines in veterinary parasitology, is the fact that it is cheek by jowl with the Onderstepoort Veterinary Institute. In the 70 years since the establishment of the Faculty of Veterinary Science the symbiotic tradition of co-operation that has developed between these two institutions contributes materially to the thorough grounding the students receive in veterinary parasitology.
Acknowledgements Many colleagues very generously provided me with study guides and other information on the courses they teach; they include Professors I. Beveridge, J. Boomker, R.C. Chhabra, J. Duncan, P. Fripp, M. Issacson, D. Jacobs, A. Lewis, B.E. Matthews, M. Sewell, C. Short, R.J. Thomas, R.C.A. Thompson and Dr P. Sauer. I am also most grateful to Dr Jane Walker, Professor I.G. Horak, Professor R. Connor and Professor R.C. Krecek for their assistance with the manuscript.
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