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Leishmaniasis in Sardinia. 5. Leishmanin reaction in the human population of a focus of low endemicity of canine leishmaniasis
TRANSACTIONS OFTHEROYALSOCIETY OFTROPICAL MEDICINE ANDHYGIENE
371
(1990) 84, 371-374
Leishmaniasis in Sardinia. 5. Leishmanin reaction in the human population of a focus of low endemicity of canine leishmaniasis M. Gramiccia’, S. Bettini’, L. Gradoni’, P. Ciarmoli’, M. L. Verrilli3, S. Loddo* and C. Cicalb’ ‘Laboratorio di Parassitologia, Istituto Superiore di Sanitc?, Viale Regina Elena 299, 00161 Roma, Italy; 21stituto di Genetica ‘Carlo Jucci’, (CS), Italy
Universitci di CagZiari, Cagliuri,
Abstract About half (640 subjects) of the population of Soleminis, a canine leishmaniasis focus 15 km north of Cagliari, Sardinia, was subjected to the leishmanin skin test. The total nositive rate was 9.7%. and that of males was 15.5%. the age trend in the positive rate resembled a hyperbolic curve, with the O-5 years age group rate being zero and the highest rate (39.3%) occurring in the 55-65 years age group. The Soleminis focus was classified as hypoendemic, with a prevalence of canine leishmaniasis of about 3%. Dog surveillance, land reclamation and changesin population habits during the last few decadesare considered to be responsible for the reduction of transmission to man. Introduction The widespread occurrence of canine leishmaniasis throughout Sardinia (BEITINI et al., 1985) led us to investigate the relationship between canine and human visceral leishmaniasis (VL) in the focus at Soleminis, Cagliari. In this note we present the results of a survey of a large sample of the human population in the town of Soleminis by meansof the leishmanin skin test (LST). We also compare our results with those reported from other Italian foci. Place The town of Soleminis, altitude 211 m, lies 15 km north of Cagliari and is surrounded by hilly cultivated land. Its records date back to the seventeenthcentury. The local population, part devoted to agriculture and part commuting daily to Cagliari, is about 1300 people. The population has gradually increased since 1901 (366 inhabitants). Epidemiological situation To our knowledge, no case of cutaneous leishmaniasis (CL) has been recorded from Soleminis or its environs. A few caseshave been reported from the area surrounding Cagliari and from localities more than 10 km from Soleminis (BETTINI et al., 1990). Similarly, no patent VL cases‘seemto have &cur&d in the territorv of Soleminis. though before 1930a few cases were reported from- Sin&i, 5 km south of Soleminis, and from the area surrounding Cagliari (FRANCO,1933). In recent years, casesof canine leishmaniasis were discovered in Soleminis, where there were about 1SO dogs. A serological noint prevalence survey showed one positive d>g &ong -38 tested (2.6%) by the indirect immunofluorescence antibodv test (IFAT). Altogether, 3 Leishmania isolates have-been dbtainkd
Italy;
3Medical Officer, Soleminis
in the last few years. The isolates were typed as L. infanturn sensu strict0 (zvmodeme MON 1= LON 49) (&AMICCIA et al., 19‘86).Two dogs were also found
oositive bv IFAT in the town of Do&nova. 3 km &orth of Soleminis. Studies on santies in the outskirts of Soleminis showed a predominance of Phlebotomus pemiciosus (BETTINI et al., 1983a), the sandflv sneciesincriminated as a vecto; of L. &fantum in &dinia (BETTINI et al., 1986b), and led to the discovery of the important sandfly larval breeding site (BETTINI et al., 1986a), the soil of which was analysed (BETTINI & MELIS, 1988). Materials and Methods Leishmanin was orenared from the WHO reference strain of L. infankm’ (MHOM/TN/IO/IPTl). This strain shows antigenic similiarity with all the other L. infanturn zymodemesaffecting man in Italy, including the dermotropic ones (our unpublished observations). Promastigotes,recently transformed from amastigotes of hamster o&n, were grown in Schneider’s me&m (HENDRICKSet al.. 1978) at 225°C and harvested during the log pLase of growth (days 4-5). The parasites were washed 4 times in pyrogen-free saline &d resuspendedin the samesolutibn containing 0.5% distilled phenol (v/v) to obtain a final concentration of 5 X lo6 0iganismS per ml. Leishmanin preparation was performed according to the safety procedures described in WHO guidelines (WHO, 1982, 1985) and in the Italian Official Pharmacopoeia. Copies of a poster, on which skin test principles and aims were briefly explained, were distributed to the local population. The few people doubting the innocuousness of the test were convinced by the local physician. Skin testing was performed on 18 and 19 May, 1989, at the town physician’s outpatient department, and skin test reactions were read 48 h after inoculation. Using a 1 ml tuberculin syringe with a no. 26 gauge needle, 0.1 ml of leishmanin, corresponding to 5 x lo5 parasites, was injected into the dermis of the inner surface of the left forearm. Previous trials with a jet-injector (Pan-Jet@:Shuco, UK) had given unsatisfactory results in somepositive cases, due to deep induration involving the subcutaneous tissues instead of the classical dermal reaction resulting from intradermal injection. Skin reaction was read by the ball-point pen method described by SOKAL(1975), calculating the averageof 2 perpendicular diameters of the dermal induration. All reactions with an induration size of 5 mm or more were recorded as positive.
372 Table. Response to leishmanin
skin test of males and females belonging to diierent
Male
o-s 5-15 15-25 25-35 35-45
:z 265
Female
No.
No. positive
tested
No.
w-1
tested
i: 52
3: 17 :;:
Total 264 41 (15.5) ‘Male:femaleratio of percentagespositive.
2 :i54 z: 30 376
so I
yr* Fig. 1. Responseto the leishmanin skin test according to age of 640 subjects in Soleminis, Sardinia (0) and of 1818 subjects in Monte Argentaria, Tuscany (A).
Fig. 2. Distribution of extent of reaction to leishmanin among the positive subjects in Soleminis, Sardinia.
Results
age groups in Soleminis,
The results of skin tests analysed according to age groups are reported in the Table. Subjects recently arriving from non-endemic areas (5 females) have been included according to the time spent in the focus. 645 subjects (about one-half of the population) were tested, 640 of whom (99.2%) were examined for skin reaction evaluation. 62 subjects were positive (9.7%): 41 of 264 males (15.5%) and 21 of 376 females (5.6%); the sex difference was highly sigrmicant (x2=16.41, 1 degreeof freedom.,~~0401). The ratio between male and female posiuvity rates increased
No. positive (%I
01 (1.1)
2 (2.9) 1 (2.3) 3 (5.6) 4 (11.8) 6 (18.7j 4 (13.3) 21 (5.6)
Total
No.
No. tested
positive (%)
32 179 122
2” (1.1) 5 (4.1)
E 2 58 640
Sardinia
: g:;j 8 (15.7)
:: tgz{
Sex
ratio” : 1.8
;:; ::;
62 (9.7)
with age, from 2.0 in the 15-25 years agegroup to 3.5 in the 55-65 years age group. Fig. 1 shows the trend of positivity rate according to age, which follows an approximately hyperbolic curve, reaching its highest level at the 55-65 years age group, after which it drops abruptly. The Figure includes the positivity values obtained for 1818 subjects in Monte Argentario, Tuscany (BETTINI et al., 1983b), for comparison. Fig. 2 shows the distribution of reaction sizes (25 mm) to leishmanin among the positive subjects. The highest frequency coincides with an induration diameter of 8-11 mm, the maximum diameter being 23 mm. Positive subjects appeared to be scattered throughout the town. Three instances of intra-familiar concentration of positive subjects were found: 2, 3 and 5 brothers belonging to 3 different households. Discussion
At present, the leishmaniasis focus of Soleminis seemsto be hypoendemic becauseof the low positivity rates in the younger age groups and the low overall shin test positivity rate (9*7%), the lowest so far recorded in leishmaniasis surveys. When the epidemiological conditions of a leishmaniasis focus are constant throughout several years, the skin test positivity rates according to age lie on a straight line, the slope of which dependson the rate of contact between parasite and man. A situation approximating to this is shown by the Monte Argentario focus (Fig. 1). In the CL focus in Teramo, Abruzzi (PAMPIGLIONE et aE., 1976), and in the mixed VL and CL inland foci of Tuscany (BETTINI et al., 1977), the skin test positivity rates follow a similar trend. But if the epidemiological conditions vary, due to decreasedvector density, number of infected dogs, or a change in the habits of the population, in such a way that the overall shorter exposure time is reduced, the parasite-man contact rate would differ from the expected value. In Soleminis, the positivity rates in the age groups from 15 to 45 years were considerably lower than those expected, thus producing a graph resembling a hyperbolic curve. It could be inferred, therefore, that in the 1940s the epidemiological conditions of leishmaniasis in Soleminis must have changed substantially. It should be recalled that in 1946-1950, during the anopheline eradication campaign, a very large amount of DDT was applied in
373 houses and in mosquito larval breeding sites throughout Sardinia (LOGAN, 1953). The sandfly density and, indirectly, the canine leishmaniasis prevalence, could have been affected by the insecticide. Furthermore, the interruption of malaria transmission led to profound changes in the economy, and consequently in the social habits of the Sardinian population (CASSANO, 1981). On the other hand, in the territory
of
Monte Argentario where there had been no malaria transmission, no anopheline control was carried out after 1947. A change in epidetniological conditions similar to
that in Soleminis probably also occurred in eastern Sicily, where the leishmanin skin test positivity rate according to age was also represented by a hyperbolic curve (PAMPIGLIONE ef al., 1975). An interruption of the ascending trend of the graph in the older age groups appears in most of the reported leishmanin skin test surveys reported in the literature. Its causeis not clear, and several explanations have been given by BETTINI et al. (1983b). In addition, a decreasedresponseto leishmanin due to a general reduction of cell-mediated reactivity in older subjects cannot be excluded. The orevalenceof canine leishmaniasis in Soleminis was lo& (about 3%), compared with that in Monte Argentario (about 24%) (GRADONI et al., 1980). The skin test positivity rate in the younger age groups (O-15 years) was also much lower in Soleminis (O-1.1%) than in Monte Argentario (4.4-10.6%). Thus the level of canine infection corresponds to the skin test positivity rate in the younger age groups. Each of these 2 quantities, therefore, concurs in indicating the degree of L&mania transmission to the human population. It could thus be inferred that the routine practice of canine health surveillance and disease control and land reclamation carried out in Soleminis during the last decades has positively influenced transmission. According to the local authorities, in the last years no important changes occurred in the habits of the population. In other Italian foci, the leishmanin skin test positivity rate of males was only slightly higher than that of females (PAMPIGLIONE et al., 1976; BETTINI et al., 1977, 1983b). The greater difference of positivity between sexes, starting in the 15-25 age group, observedin Soleminis, is therefore unusual and points to a marked difference in habits between sexes. The tendency of women to work indoors during the time of day when transmission occurs, together with the exophily of the vector P. perniciosus (ADLER & THEODOR, 1935), may explain this difference. No correlation was found between the diameter of the induration produced by a Iixed doseof leishmanin (0.1 ml) and the age or sex of the subjects tested. It seemsrather that this depends on the allergic state of the individual subjects. Our present results confirm that the analysis of leishmanin skin test data may throw light on the past and recent history of parasite-man contact in an endemic area of leishmaniasis. Acknowledgements
Thanks are due to Mr U. Argiolas, former Mayor of Soleminis, for allowing the survey to be carried out and providing facilities. We are also grateful to the present Mayor, Mr G. Sanna, for kindly giving us data on the town’s
population. Thanks are also due to Dr Teresina Mura for her valuable help during the survey. This investigation received financial support from the UNDP/World BankWHO Special Programme for Research and Training in Tropical Diseases. References
Adler, S. & Theodor, 0. (1935). Investigations of Mediterranean kala-azar. VIII. Further observations on Mediterranean sandflies. Proceedings of the Royal Society of London, B, 116, 505-515.
Bettini, S. & Melis, P. (1988). Leishmaniasis in Sardinia. III. Soil analysis of a breeding site of three species of sandflies. Medical and Veterinary Entomology, 2, 67-71. Bettini, S., Pampiglionq, S. & Maroli, M. (1977). Studies on Mediterranean leishmaniasis. V. A preliminary epidemiological survey of human leishmaniasis in Tuscany. Transactions of the Royal Society of Tropical Medicine and Hygiene, 71, 7>79.
Bettini, S., Contini, C., Maroli, M., Tocco, G. & Sigon, M. (1983a). Nota preliminare sullo studio dei vettori delle leishmaniosi in Sardegna. Parassitologia, 25, 206209. Bettini, S., Gramiccia, M., Gradoni? L., Pozio, E., Mugnai, S. & Maroli, M. (1983b). Lershmaniasis in Tuscany (Italy): VIII. Human population response to leishmanin in the focus of Monte Argentario (Grosseto) and epidemiological evaluation. Annales de Parasitologic Humaine et Compart+e, 58, 539-547.
Bettini, S., Coni, V., Scarano,C., Cogoni, M. & Atzeni, M. C. (1985). Aspetti recenti della leishmaniosi canina nelle province di Cagliari e Oristano: segnalazionedi 123casi. Progress0 Veterinario, 40, 77-80.
Bettini, S., Contini, C., Atzeni, M. C. & TOCCO, G. (1986a). Leishmaniasis in Sardinia. I. Observations on a larval breeding site of Phlebotomus pemiciosus, Phlebotomus perfiliewi and Sergentomyiaminuta (Diptera: Psychodidae) in the canine leishmaniasis focus of Soleminis, Cagliari. Annals of Tropical Medicine and Parasitology, 80, 307315. ___.
Bettini, S., Gramiccia, M., Gradoni, L. & Atzeni, M. C. (1986b). Leishmaniasis in Sardinia: II. Natural infection of Ph&botomus perniciosus Newstead, 1911, by Leishmania infanturn Nicolle, 1908,in the province of Cagliari. Transactions of the Royal Soctery of Tropical Medicine and Hygiene, 80, 458-459.
Bettini, S., Gramiccia, M., Gradoni, L., Biggio, P., Loi, R., Cottoni, F., Pau! M. & Atzeni, M. C. (1990). Leishmaniasis in Sardmia. IV. Epidemiological appraisal of cutaneousleishmaniasisand biochemical characterization of isolates. Journal of Tropical Medin’ne and Hygiene, in press. Cassano,A. (1981). La Sardegna Liberata dalla Malaria e la Riforma economica. Sassari: Gal&i. France, E. E. (1933). La leishmaniosi in Sardegna. In: Hygibne Mbditewankenne, I” Congrke International (Marseille,’ 20-25 Septembre, 1932). Paris: Bailliere, vol. 1, pp. 277-303.
Gradoni, L., Pozio, E., Bettini, S. & Gramiccia, M. (1980). Leishmaniasis in Tuscany (Italy). (III) The prevalence of canine leishmaniasis in two foci of Grosset0 Province. Transactions of the Royal Society of Tropical Medicine and Hygiene, 74, 421-422.
Gramiccia! M.,, Gradoni, L. & Pozio, E. (1986). Caracterisation btochtique de souches du complexe Leishmania infanturn isolees en Italie. In: Leishmania. Taxonomie et phylogenhse. Applications Ice-t$idkmiologiques. (Colloclue interne CNRSIINSERM, 1984). Montpellier: IMEEE, pp. 445-454. Hendricks, L. D., Wood, D. E. & Hajduk, M. E. (1978). Haemoflagellates: commercially available liquid media for rapid cultivation. Parasitology, 76, 309-316. Logan, J. A. (1953). The Sardinian Project. American Journal of Hygiene, Monograph series no. 20. Pampiglione, S., Manson-Bahr, P. E. C., La Placa, M., Borgatti, M. A. & Musumeci, S. (1975). Studies in
374 Mediterranean leishmaniasis. 3. The leishmanin skin test in kala-azar. Transactions of the Royal Society of Tropical Medicine and Hygiene, 69, 60-68.
Pampiglione, S., Manson-Bahr, P. E. C., La Placa, M., Borgatti, M. A. & Micheloni, F. (1976). Studies on Mediterranean leishmaniasis. IV. The leishmanin skin test in cutaneousleishmaniasis. Transactions of tke Royal Society of Tropical Medicine and Hygiene, 70, 62-65. Sokal, J. E. (1975). Measurement of delayed skin-test responses. New England Journal of Medicine, 293, 501-502. WHO (1982). Report of the Fourth Meeting of the Scientific
Working Group on Immunology of Leishmaniases, Geneva, 13-l 7 September 1982. Geneva: World Health Organiza-
tion, mimeographed document no. TDNLEISH-SWG (4)/82*3. WHO (1985). Expert Committee on Biological Standardiza-
tion, Geneva, 12-18 November 1985. Proposed Requiremerits for Tube&ins. Geneva: World Health Organiza-
tion, mimeographed document no. WHO/BW/85.1463 Rev. 1.
Received 29 November December I989
1989; accepted
for publication
21
TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE (1990) 84, OOWIOO
1 BookReview Appropriate
Technology
in Vector Control.
C. F.
Curtis (editor), 1990. Boca Raton, Florida: CRC Press, 233 pp. Price US$25.00. ISBN 0 8493 4755 6. Although the massive deployment of synthetic insecticides such as DDT has succeededin reducing the incidence of the major vector-borne diseasesthat afflict mainly the poorer, developing countries of the Third World, technical and socio-economic barriers have arisen that necessitatea radically new approach to the problem. Community run, small-scale technology of the kind currently labelled ‘appropriate’ or ‘intermediate’, is rapidly coming to be acceptedas an alternative, or supplementary, and generally ‘greener’ way of tackling the difficulties that have arisen. As the editor of this book points out in his introduction, a place remains, nevertheless, for the continuing use, in defined circumstances, of the now classical pesticides. It is interesting that nearly all the 13 chapters in this book are produced by an international team, and this reflects the close collaborative approach that is being followed in the field of vector and pest control today. Several common themes run throughout this work, which covers most of the vector-borne diseases. Synthetic pyrethroids are being used extensively in the control of malaria (especially for the impregnation of bed nets) and African trypanosomiasis (in tsetsefly traps). Emphasis is being laid on means of preventing insects biting human hosts. Insect repellents such as
meta-diethyltoluamide have come into their own against vector
and other biting insects. Measures of genetic control include the release of sterile male mosquitoes and tsetse flies, the trapping of insects with sound- or pheromone-baited traps and the use of juvenile hormones to control Glossitza.More extensive use is being made of larvivorous fish to control mosquito larvae and expanded polystyrene beadshave proved very valuable in controlling the breeding of
Simulium
1
and pest mosquitoes,
as well
as
culicines in static sites such as pit latrines.
Ultimately all vector control methods require not simply co-operation of the community but active community
participation,
whether this involves the
use of impregnated mosquito nets, clearance of breeding sites of filaria-carrying culicines, siting and maintenance
of tsetse traps, -fish culture,
or the
construction of modified housing and sanitarv facilities. This book contains a wealth of data illustrating the advantages of ‘appropriate’ techniques and the gains achieved by their deployment, aswell assomeof the disadvantageswhich are succinctly set out at the beginning of each chapter. The illustrations are clear and informative. The editor is to be congratulated on his successin steering his many contributors towards the production
of a uniformly
readable, as well as
info&native, review of the state of the art in applying relativelv simole technologv to the tackling of the major v&tor-Gorne diseaseiihat continue to beset the majority of the world’s population. The book should
be compulsory reading for all medical, paramedical and public health workers concerned with the organization of vector control, especially in the tropics and subtropics. W. Peters
371
(1990) 84, 371-374
Leishmaniasis in Sardinia. 5. Leishmanin reaction in the human population of a focus of low endemicity of canine leishmaniasis M. Gramiccia’, S. Bettini’, L. Gradoni’, P. Ciarmoli’, M. L. Verrilli3, S. Loddo* and C. Cicalb’ ‘Laboratorio di Parassitologia, Istituto Superiore di Sanitc?, Viale Regina Elena 299, 00161 Roma, Italy; 21stituto di Genetica ‘Carlo Jucci’, (CS), Italy
Universitci di CagZiari, Cagliuri,
Abstract About half (640 subjects) of the population of Soleminis, a canine leishmaniasis focus 15 km north of Cagliari, Sardinia, was subjected to the leishmanin skin test. The total nositive rate was 9.7%. and that of males was 15.5%. the age trend in the positive rate resembled a hyperbolic curve, with the O-5 years age group rate being zero and the highest rate (39.3%) occurring in the 55-65 years age group. The Soleminis focus was classified as hypoendemic, with a prevalence of canine leishmaniasis of about 3%. Dog surveillance, land reclamation and changesin population habits during the last few decadesare considered to be responsible for the reduction of transmission to man. Introduction The widespread occurrence of canine leishmaniasis throughout Sardinia (BEITINI et al., 1985) led us to investigate the relationship between canine and human visceral leishmaniasis (VL) in the focus at Soleminis, Cagliari. In this note we present the results of a survey of a large sample of the human population in the town of Soleminis by meansof the leishmanin skin test (LST). We also compare our results with those reported from other Italian foci. Place The town of Soleminis, altitude 211 m, lies 15 km north of Cagliari and is surrounded by hilly cultivated land. Its records date back to the seventeenthcentury. The local population, part devoted to agriculture and part commuting daily to Cagliari, is about 1300 people. The population has gradually increased since 1901 (366 inhabitants). Epidemiological situation To our knowledge, no case of cutaneous leishmaniasis (CL) has been recorded from Soleminis or its environs. A few caseshave been reported from the area surrounding Cagliari and from localities more than 10 km from Soleminis (BETTINI et al., 1990). Similarly, no patent VL cases‘seemto have &cur&d in the territorv of Soleminis. though before 1930a few cases were reported from- Sin&i, 5 km south of Soleminis, and from the area surrounding Cagliari (FRANCO,1933). In recent years, casesof canine leishmaniasis were discovered in Soleminis, where there were about 1SO dogs. A serological noint prevalence survey showed one positive d>g &ong -38 tested (2.6%) by the indirect immunofluorescence antibodv test (IFAT). Altogether, 3 Leishmania isolates have-been dbtainkd
Italy;
3Medical Officer, Soleminis
in the last few years. The isolates were typed as L. infanturn sensu strict0 (zvmodeme MON 1= LON 49) (&AMICCIA et al., 19‘86).Two dogs were also found
oositive bv IFAT in the town of Do&nova. 3 km &orth of Soleminis. Studies on santies in the outskirts of Soleminis showed a predominance of Phlebotomus pemiciosus (BETTINI et al., 1983a), the sandflv sneciesincriminated as a vecto; of L. &fantum in &dinia (BETTINI et al., 1986b), and led to the discovery of the important sandfly larval breeding site (BETTINI et al., 1986a), the soil of which was analysed (BETTINI & MELIS, 1988). Materials and Methods Leishmanin was orenared from the WHO reference strain of L. infankm’ (MHOM/TN/IO/IPTl). This strain shows antigenic similiarity with all the other L. infanturn zymodemesaffecting man in Italy, including the dermotropic ones (our unpublished observations). Promastigotes,recently transformed from amastigotes of hamster o&n, were grown in Schneider’s me&m (HENDRICKSet al.. 1978) at 225°C and harvested during the log pLase of growth (days 4-5). The parasites were washed 4 times in pyrogen-free saline &d resuspendedin the samesolutibn containing 0.5% distilled phenol (v/v) to obtain a final concentration of 5 X lo6 0iganismS per ml. Leishmanin preparation was performed according to the safety procedures described in WHO guidelines (WHO, 1982, 1985) and in the Italian Official Pharmacopoeia. Copies of a poster, on which skin test principles and aims were briefly explained, were distributed to the local population. The few people doubting the innocuousness of the test were convinced by the local physician. Skin testing was performed on 18 and 19 May, 1989, at the town physician’s outpatient department, and skin test reactions were read 48 h after inoculation. Using a 1 ml tuberculin syringe with a no. 26 gauge needle, 0.1 ml of leishmanin, corresponding to 5 x lo5 parasites, was injected into the dermis of the inner surface of the left forearm. Previous trials with a jet-injector (Pan-Jet@:Shuco, UK) had given unsatisfactory results in somepositive cases, due to deep induration involving the subcutaneous tissues instead of the classical dermal reaction resulting from intradermal injection. Skin reaction was read by the ball-point pen method described by SOKAL(1975), calculating the averageof 2 perpendicular diameters of the dermal induration. All reactions with an induration size of 5 mm or more were recorded as positive.
372 Table. Response to leishmanin
skin test of males and females belonging to diierent
Male
o-s 5-15 15-25 25-35 35-45
:z 265
Female
No.
No. positive
tested
No.
w-1
tested
i: 52
3: 17 :;:
Total 264 41 (15.5) ‘Male:femaleratio of percentagespositive.
2 :i54 z: 30 376
so I
yr* Fig. 1. Responseto the leishmanin skin test according to age of 640 subjects in Soleminis, Sardinia (0) and of 1818 subjects in Monte Argentaria, Tuscany (A).
Fig. 2. Distribution of extent of reaction to leishmanin among the positive subjects in Soleminis, Sardinia.
Results
age groups in Soleminis,
The results of skin tests analysed according to age groups are reported in the Table. Subjects recently arriving from non-endemic areas (5 females) have been included according to the time spent in the focus. 645 subjects (about one-half of the population) were tested, 640 of whom (99.2%) were examined for skin reaction evaluation. 62 subjects were positive (9.7%): 41 of 264 males (15.5%) and 21 of 376 females (5.6%); the sex difference was highly sigrmicant (x2=16.41, 1 degreeof freedom.,~~0401). The ratio between male and female posiuvity rates increased
No. positive (%I
01 (1.1)
2 (2.9) 1 (2.3) 3 (5.6) 4 (11.8) 6 (18.7j 4 (13.3) 21 (5.6)
Total
No.
No. tested
positive (%)
32 179 122
2” (1.1) 5 (4.1)
E 2 58 640
Sardinia
: g:;j 8 (15.7)
:: tgz{
Sex
ratio” : 1.8
;:; ::;
62 (9.7)
with age, from 2.0 in the 15-25 years agegroup to 3.5 in the 55-65 years age group. Fig. 1 shows the trend of positivity rate according to age, which follows an approximately hyperbolic curve, reaching its highest level at the 55-65 years age group, after which it drops abruptly. The Figure includes the positivity values obtained for 1818 subjects in Monte Argentario, Tuscany (BETTINI et al., 1983b), for comparison. Fig. 2 shows the distribution of reaction sizes (25 mm) to leishmanin among the positive subjects. The highest frequency coincides with an induration diameter of 8-11 mm, the maximum diameter being 23 mm. Positive subjects appeared to be scattered throughout the town. Three instances of intra-familiar concentration of positive subjects were found: 2, 3 and 5 brothers belonging to 3 different households. Discussion
At present, the leishmaniasis focus of Soleminis seemsto be hypoendemic becauseof the low positivity rates in the younger age groups and the low overall shin test positivity rate (9*7%), the lowest so far recorded in leishmaniasis surveys. When the epidemiological conditions of a leishmaniasis focus are constant throughout several years, the skin test positivity rates according to age lie on a straight line, the slope of which dependson the rate of contact between parasite and man. A situation approximating to this is shown by the Monte Argentario focus (Fig. 1). In the CL focus in Teramo, Abruzzi (PAMPIGLIONE et aE., 1976), and in the mixed VL and CL inland foci of Tuscany (BETTINI et al., 1977), the skin test positivity rates follow a similar trend. But if the epidemiological conditions vary, due to decreasedvector density, number of infected dogs, or a change in the habits of the population, in such a way that the overall shorter exposure time is reduced, the parasite-man contact rate would differ from the expected value. In Soleminis, the positivity rates in the age groups from 15 to 45 years were considerably lower than those expected, thus producing a graph resembling a hyperbolic curve. It could be inferred, therefore, that in the 1940s the epidemiological conditions of leishmaniasis in Soleminis must have changed substantially. It should be recalled that in 1946-1950, during the anopheline eradication campaign, a very large amount of DDT was applied in
373 houses and in mosquito larval breeding sites throughout Sardinia (LOGAN, 1953). The sandfly density and, indirectly, the canine leishmaniasis prevalence, could have been affected by the insecticide. Furthermore, the interruption of malaria transmission led to profound changes in the economy, and consequently in the social habits of the Sardinian population (CASSANO, 1981). On the other hand, in the territory
of
Monte Argentario where there had been no malaria transmission, no anopheline control was carried out after 1947. A change in epidetniological conditions similar to
that in Soleminis probably also occurred in eastern Sicily, where the leishmanin skin test positivity rate according to age was also represented by a hyperbolic curve (PAMPIGLIONE ef al., 1975). An interruption of the ascending trend of the graph in the older age groups appears in most of the reported leishmanin skin test surveys reported in the literature. Its causeis not clear, and several explanations have been given by BETTINI et al. (1983b). In addition, a decreasedresponseto leishmanin due to a general reduction of cell-mediated reactivity in older subjects cannot be excluded. The orevalenceof canine leishmaniasis in Soleminis was lo& (about 3%), compared with that in Monte Argentario (about 24%) (GRADONI et al., 1980). The skin test positivity rate in the younger age groups (O-15 years) was also much lower in Soleminis (O-1.1%) than in Monte Argentario (4.4-10.6%). Thus the level of canine infection corresponds to the skin test positivity rate in the younger age groups. Each of these 2 quantities, therefore, concurs in indicating the degree of L&mania transmission to the human population. It could thus be inferred that the routine practice of canine health surveillance and disease control and land reclamation carried out in Soleminis during the last decades has positively influenced transmission. According to the local authorities, in the last years no important changes occurred in the habits of the population. In other Italian foci, the leishmanin skin test positivity rate of males was only slightly higher than that of females (PAMPIGLIONE et al., 1976; BETTINI et al., 1977, 1983b). The greater difference of positivity between sexes, starting in the 15-25 age group, observedin Soleminis, is therefore unusual and points to a marked difference in habits between sexes. The tendency of women to work indoors during the time of day when transmission occurs, together with the exophily of the vector P. perniciosus (ADLER & THEODOR, 1935), may explain this difference. No correlation was found between the diameter of the induration produced by a Iixed doseof leishmanin (0.1 ml) and the age or sex of the subjects tested. It seemsrather that this depends on the allergic state of the individual subjects. Our present results confirm that the analysis of leishmanin skin test data may throw light on the past and recent history of parasite-man contact in an endemic area of leishmaniasis. Acknowledgements
Thanks are due to Mr U. Argiolas, former Mayor of Soleminis, for allowing the survey to be carried out and providing facilities. We are also grateful to the present Mayor, Mr G. Sanna, for kindly giving us data on the town’s
population. Thanks are also due to Dr Teresina Mura for her valuable help during the survey. This investigation received financial support from the UNDP/World BankWHO Special Programme for Research and Training in Tropical Diseases. References
Adler, S. & Theodor, 0. (1935). Investigations of Mediterranean kala-azar. VIII. Further observations on Mediterranean sandflies. Proceedings of the Royal Society of London, B, 116, 505-515.
Bettini, S. & Melis, P. (1988). Leishmaniasis in Sardinia. III. Soil analysis of a breeding site of three species of sandflies. Medical and Veterinary Entomology, 2, 67-71. Bettini, S., Pampiglionq, S. & Maroli, M. (1977). Studies on Mediterranean leishmaniasis. V. A preliminary epidemiological survey of human leishmaniasis in Tuscany. Transactions of the Royal Society of Tropical Medicine and Hygiene, 71, 7>79.
Bettini, S., Contini, C., Maroli, M., Tocco, G. & Sigon, M. (1983a). Nota preliminare sullo studio dei vettori delle leishmaniosi in Sardegna. Parassitologia, 25, 206209. Bettini, S., Gramiccia, M., Gradoni? L., Pozio, E., Mugnai, S. & Maroli, M. (1983b). Lershmaniasis in Tuscany (Italy): VIII. Human population response to leishmanin in the focus of Monte Argentario (Grosseto) and epidemiological evaluation. Annales de Parasitologic Humaine et Compart+e, 58, 539-547.
Bettini, S., Coni, V., Scarano,C., Cogoni, M. & Atzeni, M. C. (1985). Aspetti recenti della leishmaniosi canina nelle province di Cagliari e Oristano: segnalazionedi 123casi. Progress0 Veterinario, 40, 77-80.
Bettini, S., Contini, C., Atzeni, M. C. & TOCCO, G. (1986a). Leishmaniasis in Sardinia. I. Observations on a larval breeding site of Phlebotomus pemiciosus, Phlebotomus perfiliewi and Sergentomyiaminuta (Diptera: Psychodidae) in the canine leishmaniasis focus of Soleminis, Cagliari. Annals of Tropical Medicine and Parasitology, 80, 307315. ___.
Bettini, S., Gramiccia, M., Gradoni, L. & Atzeni, M. C. (1986b). Leishmaniasis in Sardinia: II. Natural infection of Ph&botomus perniciosus Newstead, 1911, by Leishmania infanturn Nicolle, 1908,in the province of Cagliari. Transactions of the Royal Soctery of Tropical Medicine and Hygiene, 80, 458-459.
Bettini, S., Gramiccia, M., Gradoni, L., Biggio, P., Loi, R., Cottoni, F., Pau! M. & Atzeni, M. C. (1990). Leishmaniasis in Sardmia. IV. Epidemiological appraisal of cutaneousleishmaniasisand biochemical characterization of isolates. Journal of Tropical Medin’ne and Hygiene, in press. Cassano,A. (1981). La Sardegna Liberata dalla Malaria e la Riforma economica. Sassari: Gal&i. France, E. E. (1933). La leishmaniosi in Sardegna. In: Hygibne Mbditewankenne, I” Congrke International (Marseille,’ 20-25 Septembre, 1932). Paris: Bailliere, vol. 1, pp. 277-303.
Gradoni, L., Pozio, E., Bettini, S. & Gramiccia, M. (1980). Leishmaniasis in Tuscany (Italy). (III) The prevalence of canine leishmaniasis in two foci of Grosset0 Province. Transactions of the Royal Society of Tropical Medicine and Hygiene, 74, 421-422.
Gramiccia! M.,, Gradoni, L. & Pozio, E. (1986). Caracterisation btochtique de souches du complexe Leishmania infanturn isolees en Italie. In: Leishmania. Taxonomie et phylogenhse. Applications Ice-t$idkmiologiques. (Colloclue interne CNRSIINSERM, 1984). Montpellier: IMEEE, pp. 445-454. Hendricks, L. D., Wood, D. E. & Hajduk, M. E. (1978). Haemoflagellates: commercially available liquid media for rapid cultivation. Parasitology, 76, 309-316. Logan, J. A. (1953). The Sardinian Project. American Journal of Hygiene, Monograph series no. 20. Pampiglione, S., Manson-Bahr, P. E. C., La Placa, M., Borgatti, M. A. & Musumeci, S. (1975). Studies in
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Pampiglione, S., Manson-Bahr, P. E. C., La Placa, M., Borgatti, M. A. & Micheloni, F. (1976). Studies on Mediterranean leishmaniasis. IV. The leishmanin skin test in cutaneousleishmaniasis. Transactions of tke Royal Society of Tropical Medicine and Hygiene, 70, 62-65. Sokal, J. E. (1975). Measurement of delayed skin-test responses. New England Journal of Medicine, 293, 501-502. WHO (1982). Report of the Fourth Meeting of the Scientific
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Received 29 November December I989
1989; accepted
for publication
21
TRANSACTIONS OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND HYGIENE (1990) 84, OOWIOO
1 BookReview Appropriate
Technology
in Vector Control.
C. F.
Curtis (editor), 1990. Boca Raton, Florida: CRC Press, 233 pp. Price US$25.00. ISBN 0 8493 4755 6. Although the massive deployment of synthetic insecticides such as DDT has succeededin reducing the incidence of the major vector-borne diseasesthat afflict mainly the poorer, developing countries of the Third World, technical and socio-economic barriers have arisen that necessitatea radically new approach to the problem. Community run, small-scale technology of the kind currently labelled ‘appropriate’ or ‘intermediate’, is rapidly coming to be acceptedas an alternative, or supplementary, and generally ‘greener’ way of tackling the difficulties that have arisen. As the editor of this book points out in his introduction, a place remains, nevertheless, for the continuing use, in defined circumstances, of the now classical pesticides. It is interesting that nearly all the 13 chapters in this book are produced by an international team, and this reflects the close collaborative approach that is being followed in the field of vector and pest control today. Several common themes run throughout this work, which covers most of the vector-borne diseases. Synthetic pyrethroids are being used extensively in the control of malaria (especially for the impregnation of bed nets) and African trypanosomiasis (in tsetsefly traps). Emphasis is being laid on means of preventing insects biting human hosts. Insect repellents such as
meta-diethyltoluamide have come into their own against vector
and other biting insects. Measures of genetic control include the release of sterile male mosquitoes and tsetse flies, the trapping of insects with sound- or pheromone-baited traps and the use of juvenile hormones to control Glossitza.More extensive use is being made of larvivorous fish to control mosquito larvae and expanded polystyrene beadshave proved very valuable in controlling the breeding of
Simulium
1
and pest mosquitoes,
as well
as
culicines in static sites such as pit latrines.
Ultimately all vector control methods require not simply co-operation of the community but active community
participation,
whether this involves the
use of impregnated mosquito nets, clearance of breeding sites of filaria-carrying culicines, siting and maintenance
of tsetse traps, -fish culture,
or the
construction of modified housing and sanitarv facilities. This book contains a wealth of data illustrating the advantages of ‘appropriate’ techniques and the gains achieved by their deployment, aswell assomeof the disadvantageswhich are succinctly set out at the beginning of each chapter. The illustrations are clear and informative. The editor is to be congratulated on his successin steering his many contributors towards the production
of a uniformly
readable, as well as
info&native, review of the state of the art in applying relativelv simole technologv to the tackling of the major v&tor-Gorne diseaseiihat continue to beset the majority of the world’s population. The book should
be compulsory reading for all medical, paramedical and public health workers concerned with the organization of vector control, especially in the tropics and subtropics. W. Peters