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Control of coccidiosis in chickens by vaccination
Veterinary Parasitology 100 (2001) 13–20
Control of coccidiosis in chickens by vaccination A.N. Vermeulen∗ , D.C. Schaap, Th.P.M. Schetters Department of Parasitology (R&D), Intervet International BV, P.O. Box 31, 5830 AA Boxmeer, The Netherlands
Abstract Control of coccidiosis in chickens has relied upon managerial measurements and the prophylactic use of coccidiostatic drugs. With the emergence of Eimeria strains that are resistant to these drugs the use and number of commercially available vaccines has increased. In this review various aspects that contribute to the development of coccidiosis are discussed, and an overview of the currently marketed coccidiosis vaccines is presented. Three groups of vaccines can be distinguished based on the characteristics of the Eimeria species included in the products: vaccines based on live virulent strains, vaccines based on live attenuated strains, and vaccines based on live strains that are relatively tolerant to the use of ionophores. These latter vaccines combine the early protective effect of ionophore treatment with the late protective effect of vaccination. The impact of future developments such as recombinant-DNA vaccines and changes in consumer’s attitude towards broiler production are discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Eimeria; Chickens; Vaccination; Live vaccine; Recombinant-DNA
1. Introduction Coccidiosis in poultry is caused by infection with parasites of one or more Eimeria species. Seven Eimeria species have been recognized to infect chickens: Eimeria acervulina, E. maxima, E. tenella, E. brunetti, E. necatrix, E. mitis and E. praecox. Each species has its own characteristics with respect to prevalence, site of infection, pathogenicity, and immunogenicity (Rose and Long, 1980). All species, however, parasitise the epithelial cells of the intestinal lining causing pathological changes varying from local destruction of the mucosal barrier and underlying tissue (often associated with some degree of inflammation resulting in endothelial lesions), to systemic effects such as blood loss, shock syndrome and even death. Although in most cases immunity develops after repeated infections, the infection leads to economic losses resulting from drop in egg production or malabsorption (poor ∗ Corresponding author. Tel.: +31-485-587370; fax: +31-485-587339. E-mail address: [email protected] (A.N. Vermeulen).
0304-4017/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 0 1 7 ( 0 1 ) 0 0 4 7 9 - 4
14
A.N. Vermeulen et al. / Veterinary Parasitology 100 (2001) 13–20
weight gains or feed conversion), even in the absence of clinical symptoms (sub-clinical coccidiosis). Williams (1999) recently estimated that losses due to coccidiosis in chicken industry in 1995 were approximately 40 million pounds Sterling on a production of 625 million broilers in UK. An important aspect in this estimation was that only 17.5% of these were attributed to the costs of prophylaxis and treatment, and around 80% due to losses on feed conversion and weight gain in the presence of drug-treatment strategies. One has to conclude that especially in the broiler industry, there is a need for new strategic concepts to control coccidiosis. Here we review various aspects that contribute to the development of coccidiosis, and ways to control this disease, with an emphasis on the use of vaccines.
2. Factors affecting the outcome of infection 2.1. Age Resistance to Eimeria infection is often age-related. In the field of chicken coccidiosis young animals are generally considered as less susceptible, although the parasite infects the chickens the damage done is often limited (Voeten et al., 1988; Ruff, 1993). 2.2. Genetic background Proliferation of the parasites, severity of lesions and effects on weight gain are very much determined by the genetic background of the host (Long, 1970), possibly related to the potential to develop immunity to infection (Clare et al., 1985). Jeffers and Shirley (1982) concluded that such resistance is mainly caused by the total of the genetic background resulting from the combination of genomes from diverse breeds and not so much by inheritance of one or more specific ‘resistance’ genes. Furthermore, it was demonstrated that inbred lines of White Leghorns selected for resistance to a specific Eimeria species were sometimes more susceptible to another species (Bumstead and Millard, 1992). 2.3. Concurrent infections Besides the genetic factors playing a role in the final outcome of the infection, interference of simultaneous infection with different Eimeria species and interactions with other pathogens such as viruses and enteric bacteria can determine the severity of the disease. Interactions have been shown for Reovirus, Marek’s Disease Virus, Newcastle Disease Virus and Infectious Bronchitis Virus, mostly aggravating the symptoms of both infections (Ruff, 1993). Managerial factors, like poor hygiene, presence of other animals on the farm, the use of in-feed medication and the occurrence of other infectious diseases in the present or previous flock all affect the spread of the disease and the severity of the infection (Graat et al., 1998). For instance, increasing problems associated with concurrent infections of Eimeria and Clostridium perfringens or E. coli have been reported, especially in Nordic countries where antibiotics are banned from use in broiler management (Van der Stroom and van der Sluis, 1999).
A.N. Vermeulen et al. / Veterinary Parasitology 100 (2001) 13–20
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3. Control strategies 3.1. In-feed prophylactic medication Reduction of infection pressure is the first measure to control coccidiosis outbreaks. Cleaning of the broiler house between consecutive rounds is important, but some infective oocysts will survive any practical cleaning procedure. If left untreated infection will gradually build up in the flock during the growing period and can cause coccidiosis in chickens that have developed no or only partial immunity. To reduce the risk of contracting an infection, prophylactic ‘in-feed’ medication is being used with considerable success. However, the abundant use of anti-coccidials has resulted in the selection for drug resistant strains, which has reduced the efficacy of many of the currently used coccidiostats (Chapman, 1993, 1999; Vertommen et al., 1990). As in many countries legislation prohibits the use of medication until slaughter, withdrawal periods of the medication have been imposed, which further increases the risk of developing infection at the end of the growing period. Thus, when coccidiostats are used to control coccidiosis, the risk for coccidiosis to develop in a flock gradually increases with age (increase of infection pressure) with maximal risk during the withdrawal period. To further limit selection of drug-resistant strains, shuttle and rotation programs have been introduced in which different coccidiostats are alternately used, either within a single flock or in a series of consecutive flocks. 3.2. Vaccination When chickens are infected with low numbers of Eimeria parasites, protective immunity is induced after two to three consecutive infections (Joyner and Norton, 1973; Long et al., 1986). All commercially available coccidiosis vaccines are based on this principle (Table 1). Depending on the characteristics of the vaccine strains used, these vaccines can be roughly divided in three groups. Table 1 Commercially available vaccines against chicken coccidiosis Trade name
Attenuated
Ionophore tolerance
Speciesa
Applicationb
Manufacturer
Coccivac D Coccivac B Immucox C1 Immucox C2 Paracox Paracox 5 Livacox D Livacox T Nobilis COX ATM
No No No No Yes Yes Yes Yes No
No No No No No No No No Yes
A, T, M, N, B, P, H, Miv A, T, M, Miv A, T, M, N A, T, M, N, B, Mi, P A, T, M2, N, B, Mi, P A, T, M2, Mi A, T A, T, M A, T, M2
DW DW/SB DW/G DW DW SF DW DW DW/SB
Schering plough Schering plough Vetech labs Vetech labs Schering plough Schering plough Biopharm Biopharm Intervet
a Species: E. acervulina (A), E. tenella (T), E. maxima (M), E. necatrix (N), E. brunetti (B), E. mitis (Mi), E. mivati (Miv), E. hagani (H), E. praecox (P). M2 means two antigenically different strains of E. maxima. b Applications: drinking water (DW), spray on birds (SB), spray on feed (SF), oral gel (G).
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3.2.1. Live, virulent strains These vaccines comprise a variable number of wild type strains depending on their formulation and field of application (Lee, 1987). For broiler-breeders up to eight Eimeria species are included in these products (Coccivac® D, Immucox® C2). For use in the broiler industry this number is restricted to up to four species (Coccivac® B, Immucox® C1). 3.2.2. Live, attenuated strains Attenuated lines of Eimeria parasites can be obtained by repeated selection for early maturation (pre-cociousness) or serial passage through embryonated eggs (TA lines) (Long, 1972; Jeffers, 1975). The most important feature of these lines is their reduced proliferative capacity resulting in less damage to the intestinal lining after one passage through the gut. This has led to the development of two attenuated vaccines, Paracox® (precocious strains; Shirley and Millard, 1986; Shirley, 1989; Williams, 1992) and Livacox® (precocious and TA strains; Bedrnik, 1989). As with the live virulent vaccines, here vaccines have been developed for different markets. Live vaccines (with either virulent or attenuated parasites) are given to chickens in the first week of age, which results in early low-level infection followed by cycling of the vaccine parasites through the litter and induction of immunity against a heavy field challenge. Any use of therapeutics or feed additives that interfere with Eimeria development cannot be used during the period of development of immunity. Thus, when vaccination is used to control coccidiosis the risk of contracting coccidiosis is highest at the early age (weeks 1–3), and decreases as immunity has developed (from weeks 3 to 4 onwards). 3.2.3. Live, tolerant to ionophores A new development has been the use of live Eimeria strains that are relatively tolerant to ionophores. An experimental vaccine comprising a strain of E. acervulina and a strain from E. maxima, both of which were partially tolerant to salinomycin, has been used in USA (Danforth, 2000). A live vaccine that can be used with different ionophores has been recently introduced (Nobilis® COX ATM, Table 1) to the market (Schetters et al., 1999). The vaccine comprises strains of three different Eimeria species (E. acervulina, E. tenella, and E. maxima) which are relatively tolerant to ionophores. As with all the vaccines described above, the risk of contracting coccidiosis is minimal after the animals have developed immunity (3–4 weeks). The advantage of these specific vaccines is that they allow the use of ionophores during the first 3–4 weeks when immunity is not complete. Such use limits the increase of infection pressure due to expanding field strains during the period of development of immunity, which further reduces the overall risk of contracting coccidiosis.
4. Factors affecting efficacy of commercially available vaccines 4.1. Route of administration Crucial to the efficient induction of protective immunity using live vaccines is the even distribution of the vaccine oocysts over the animals. As the vaccines are oral vaccines,
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administration through drinking water, and a variety of feed-based administrations have been used. The little data that are available about use in broiler flocks indicate that performance of vaccinated flocks is generally not improved over medicated flocks (Williams et al., 1999; Waldenstedt et al., 1999). Overall data even showed higher feed conversions in vaccinated over medicated flocks. This could be due to the fact that these routes of administration rely upon the initiative of the individual chicken to receive a full dose of vaccine. The hierarchy in a specific flock will affect the distribution of the vaccine over the individual animals; some receiving more than one dose, others receiving no vaccine at all. This situation is less likely to occur when the vaccine is sprayed onto the birds. Part of the vaccine will be taken up through the eyes, and part through the beak when chickens arrange their feathers. It is for this reason that spray vaccination onto the birds has recently been recommended, and the available data show that over 94% of animals vaccinated by spray had indeed taken up oocysts (Schetters et al., 1999). 4.2. Compatibility with broiler production management When administered correctly to the chickens, all available vaccines induce immunity in 3–4 weeks. However, the performance of the vaccinated chickens should (depending on the field infection pressure) be equal to or better than that of medicated non-vaccinated birds. Danforth (1998) described several trials performed on farms, throughout the USA, investigating the practical aspects of different large-scale vaccination strategies and especially parameters determining the efficacy of these vaccines. These studies demonstrated that most broiler breeds exhibited a transient slight drop in weight gain after vaccination, but recovered quickly and compensated for the loss after 3 or 4 weeks. In another series of field experiments it was shown that vaccinated flocks had higher feed conversion rates than non-vaccinated but medicated flocks (Williams et al., 1999). The improvement of feed conversion by 4% in the absence of coccidial challenge has been widely recognized for drugs such as salinomycin or maduramycin (Radu et al., 1987). One of the most interesting observations was that the combination of such ionophore treatment with vaccination could further improve the effect of vaccination or treatment alone. Data from field trials with a vaccine that could be used with ionophores support this observation (Table 2). Table 2 Performance data of the trial 1 vaccinated and historic control flocks
Nobilis COX ATM Number of broilers placed Total mortality (%) Growing period (days) Average slaughter weight (g) Average growth per day (g) Feed conversion Feed conversion 1500a European production index a
Post-trial flock
Trial flock
Pre-trial flock 1
Pre-trial flock 2
No 19500 3.3 44 2008 45.6 1.83 1.63 240
Yes 19225 3.6 44 2097 47.7 1.79 1.55 257
No 19000 4.2 45 1999 44.4 1.81 1.61 234
No 19000 9.2 43 1918 44.6 1.83 1.66 221
Standardized for 1500 g body weight.
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5. Future control of coccidiosis Live coccidiosis vaccines will be used as an aid in the control of coccidiosis in broilers. Furthermore, the possibility of ovo application (at the hatchery) which has become the method of choice for live virus vaccination in the USA (Gagic et al., 1999) remains an area of interest to improve efficacy of vaccination. Although it has been shown that sporocysts can be injected directly into the yolk sac (Dibner et al., 1999) this method seems less likely to become general practice. The development of sub-unit and recombinant vector-vaccines is being pursued (reviewed in Vermeulen, 1997; Jenkins, 1997). These strategies have the advantage that no live parasites are introduced, and the vectors used are safe and often already used in vaccines. Moreover, it is expected that immunity against the vector-organism is also induced, which is for carriers such as HVT or Salmonella certainly an advantage. Recent data from our lab show the potential of recombinant vaccines. Two different vectors (i.e. attenuated Salmonella typhimurium and herpes virus of turkeys (HVT)) were used to make constructs that expressed different antigens of each of the three Eimeria species: E. acervulina, E. tenella and E. maxima. Broilers were vaccinated at 1 day of age and challenged 2 weeks later with a mixture of oocysts of E. tenella, E. acervulina and E. maxima. Three weeks after challenge infection the vaccinated animals had significantly higher body weight than the non-vaccinated control animals. In addition, feed conversions of all vaccinated groups were over five points better than the control group (Table 3). This experiment is an example of the potency of these kinds of vaccine in the future control of coccidiosis. Broiler producers are faced with changes in public appreciation of their product. In the northern Hemisphere there is an increased demand for biological products that have been produced in a less industrialized environment. Furthermore, increased awareness of the consequences of the use of antibiotics will divert the market towards broilers that have been produced with a minimal of feed additives and antibiotics. This change in public attitude will be reflected in legislation which producers will have to comply with. Producers will have to look for alternative control measures as problems may be expected. For instance, reduction of the use of antibiotics in Sweden was associated with an increase in the incidence of necrotic enteritis (caused by Clostridium perfringens) and Escherichia coli-caused syndromes (Van der Stroom and van der Sluis, 1999). Similarly, it is envisaged that a reduction Table 3 Effect of vaccination of broiler chickens at 1 day of age with different recombinant vaccine preparation on performance after challenge infection with a mixture of E. acervulina, E. tenella and E. maxima oocystsa Treatment
Weight (g)
Feed conversion
Not treated HVT-Eim5 Salmonella-Eim5 Combi HVT/Sal Eim5
1871 ± 210 1960 ± 213∗ 1975 ± 233∗ 2036 ± 160∗
1.80 1.74 1.75 1.74
a Data represent the mean body weight and feed conversion rate (adjusted to 1500 g) at 35 days of age (3 weeks post-infection). HVT: Herpes virus of turkeys; Eim5: combination vaccine with two antigens of E. acervulina, two antigens of E. maxima, and one antigen of E. tenella. ∗ P < 0.05 different from not-treated group.
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of the use of coccidiostats will increase the risk of coccidiosis outbreaks, and it is thus expected that there will be an increased request for effective vaccines. In general, management and nutrition factors will be further improved to minimize losses due to infectious diseases. The use of immunostimulants, betaine and feeds with optimal structural characteristics will be further explored as an aid in the control of coccidiosis (Langhout, 1999). Concluding, it has become clear that the poultry production is changing both in terms of volume as well as in structure. The massive in-feed medication as has been used for antibiotics will be replaced by other means to control infectious diseases. Vaccination is clearly the best long-term solution for the problems that are looming. Improvement of the physiological and thus also immunological fitness of the animal by better hygiene management and using specific feed supplements will certainly complement this approach.
Acknowledgements We are greatly indebted to the technical staff of our laboratory for their assistance to the complicated and laborious experiments reported in this review. We like to thank especially Hay Janssen, and Drs. Goossen van den Bosch, Egbert Hanenberg and Dorothee Paeffgen for their scientific input and comments on this manuscript. References Bedrnik, P., 1989. The role of different Eimeria species in a prospective coccidiosis vaccine. In: Yvoré, P. (Ed.), Coccidia and Intestinal Coccidiomorphs. INRA, Tours, France, pp. 667–670. Bumstead, N., Millard, B.J., 1992. Variation in susceptibility of inbred lines of chickens to seven species of Eimeria. Parasitology 104, 407–413. Chapman, H.D., 1993. Twenty-one years of Monensin for the control of coccidiosis. In: Barta, J.R., Fernando, M.A. (Eds.), Proceedings of the 5th International Coccidiosis Conference, Guelph, Canada, pp. 37–45. Chapman, H.D., 1999. The development of immunity to Eimeria species in broilers given anticoccidial drugs. Avian Pathol. 28 (2), 155–162. Clare, R.A., Strout, R.G., Taylor Jr., R.L., Collins, W.M., Briles, W.E., 1985. Major histocompatibility (B) complex effects on acquired immunity to cecal coccidiosis. Immunogenetics 22, 593–599. Danforth, H.D., 1998. Use of live oocyst vaccines in the control of avian coccidiosis: experimental studies and field trials. Int. J. Parasitol. 28, 1099–1109. Danforth, H.D., 2000. Increase in anticoccidial sensitivity seen after field trial studies with five oocyst vaccination of partially drug-resistant strains of avian Eimeria species (abstract). In: Proceedings of the 75th Annual Meeting of the American Society of Parasitologists and the 53rd Annual Meeting of Protozoologists, p. 90. Dibner, J., Ivey, F.J., Knight, C.D., 1999. Direct delivery of live coccidiosis vaccine into the hatchling yolk sac. In: van der Sluis, W. (Ed.), World Poultry. Elsevier, Amsterdam, pp. 25–26. Gagic, M., St Hill, C.A., Sharma, J.M., 1999. In ovo vaccination of specific-pathogen-free chickens with vaccines containing multiple agents. Avian Dis. 43 (2), 293–301. Graat, E.A., van der Kooij, E., Frankena, K., Henken, A.M., Smeets, J.F., Hekerman, M.T., 1998. Quantifying risk factors of coccidiosis in broilers using on-farm data based on a veterinary practice. Prev. Vet. Med. 33 (1–4), 297–308. Jeffers, T.K., 1975. Attenuation of Eimeria tenella through selection for pre-cociousness. J. Parasitol. 61, 1083– 1090. Jeffers, T.K., Shirley, M.W., 1982. Genetics, specific and infraspecific variation. In: Long, P.L. (Ed.), The Biology of the Coccidia. University Park Press, USA, pp. 63–100.
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Jenkins, M.C., 1997. Progress on developing a recombinant coccidiosis vaccine. Int. J. Parasitol. 28, 1111–1121. Joyner, L.P., Norton, C.C., 1973. The immunity arising from continuous low-level infections with Eimeria tenella. Parasitology 67, 907–913. Langhout, P.J., 1999. The role of nutrition on coccidial infections. In: van der Sluis, W. (Ed.), World Poultry. Elsevier, Amsterdam, pp. 29–30. Lee, E.H., 1987. Vaccination against coccidiosis in commercial roaster chickens. Can. Vet. J. 28, 434–436. Long, P.L., 1970. Anticoccidial drugs: factors affecting the pathogenicity of avian coccidiosis. Exp. Parasitol. 28, 4–10. Long, P.L., 1972. Eimeria tenella: reproduction, pathogenicity and immunogenicity of a strain maintained in chick embryos by serial passage. J. Comp. Pathol. 82, 429–437. Long, P.L., Johnson, J., McKenzie, M.E., Perry, E., Crane, M.St.J., Murray, P.K., 1986. Immunisation of young broiler chickens with low level infections of Eimeria tenella, E. acervulina or E. maxima. Avian Pathol. 15, 271–278. Radu, J., Van Dijk, C., Wheelhouse, R.K., Hummant, C.A., Gadbois, P., 1987. Feed and water consumption and performance of male and female broilers fed salinomycin and maduramicin followed by a withdrawal ration. Poultry Sci. 66 (11), 1878–1881. Rose, M.E., Long, P.L., 1980. Vaccination against coccidiosis in chickens. In: Taylor, A.E.R., Muller, R. (Eds.), Vaccination Against Parasites. Blackwell Scientific, Oxford, UK, pp. 57–74. Ruff, M.D., 1993. External and internal factors affecting the severity of avian coccidiosis. In: Proceedings of the 6th International Coccidiosis Conference, Guelph, Ont., Canada, pp. 73–79. Schetters, T.P.M., Janssen, H.A.J.M., Vermeulen, A.N., 1999. A new vaccination concept against coccidiosis in poultry. In: van der Sluis, W. (Ed.), World Poultry. Elsevier, Amsterdam, pp. 23–24. Shirley, M.W., 1989. Development of a live attenuated vaccine against coccidiosis of poultry. Parasitol. Immunol. 11, 117–124. Shirley, M.W., Millard, B.J., 1986. Studies on the immunogenicity of seven attenuated lines of Eimeria given as a mixture to chickens. Avian Pathol. 15, 629–638. Van der Stroom, J.H., van der Sluis, W., 1999. The effect of intercurrent diseases on coccidiosis. In: van der Sluis, W. (Ed.), World Poultry. Elsevier, Amsterdam, pp. 13–14. Vermeulen, A.N., 1997. Progress in recombinant vaccine development against coccidiosis. A review and prospects into the next millennium. Int. J. Parasitol. 28, 1121–1131. Vertommen, M.H., Peek, H.W., van der Laan, A., 1990. Efficacy of toltrazuril in broilers and development of a laboratory model for sensitivity testing of Eimeria field isolates. Vet. Q. 12 (3), 183–192. Voeten, A.C., Braunius, W.W., Orthel, F.W., van Rijen, M.A., 1988. Influence of coccidiosis on growth rate and feed conversion in broilers after experimental infections with Eimeria acervulina and Eimeria maxima. Vet. Q. 10, 56–264. Waldenstedt, L., Lunden, A., Elwinger, K., Thebo, P., Uggla, A., 1999. Comparison between a live, attenuated anticoccidial vaccine and an anticoccidial ionophore, on performance of broilers raised with or without a growth promoter, in an initially Eimeria-free environment. Acta Vet. Scand. 40 (1), 11–21. Williams, R.B., 1992. The Development, Efficacy and Epidemiological Aspects of Paracox® , A New Coccidiosis Vaccine for Chickens. Harefield, Pittman-Moore, Europe. Williams, R.B., 1999. A compartmentalised model for the estimation of the cost of coccidiosis to the world’s chicken production industry. Int. J. Parasitol. 29, 1209–1229. Williams, R.B., Carlyle, W.W., Bond, D.R., Brown, I.A., 1999. The efficacy and economic benefits of Paracox, a live attenuated anticoccidial vaccine, in commercial trials with standard broiler chickens in the United Kingdom. Int. J. Parasitol. 29 (2), 341–355.
Control of coccidiosis in chickens by vaccination A.N. Vermeulen∗ , D.C. Schaap, Th.P.M. Schetters Department of Parasitology (R&D), Intervet International BV, P.O. Box 31, 5830 AA Boxmeer, The Netherlands
Abstract Control of coccidiosis in chickens has relied upon managerial measurements and the prophylactic use of coccidiostatic drugs. With the emergence of Eimeria strains that are resistant to these drugs the use and number of commercially available vaccines has increased. In this review various aspects that contribute to the development of coccidiosis are discussed, and an overview of the currently marketed coccidiosis vaccines is presented. Three groups of vaccines can be distinguished based on the characteristics of the Eimeria species included in the products: vaccines based on live virulent strains, vaccines based on live attenuated strains, and vaccines based on live strains that are relatively tolerant to the use of ionophores. These latter vaccines combine the early protective effect of ionophore treatment with the late protective effect of vaccination. The impact of future developments such as recombinant-DNA vaccines and changes in consumer’s attitude towards broiler production are discussed. © 2001 Elsevier Science B.V. All rights reserved. Keywords: Eimeria; Chickens; Vaccination; Live vaccine; Recombinant-DNA
1. Introduction Coccidiosis in poultry is caused by infection with parasites of one or more Eimeria species. Seven Eimeria species have been recognized to infect chickens: Eimeria acervulina, E. maxima, E. tenella, E. brunetti, E. necatrix, E. mitis and E. praecox. Each species has its own characteristics with respect to prevalence, site of infection, pathogenicity, and immunogenicity (Rose and Long, 1980). All species, however, parasitise the epithelial cells of the intestinal lining causing pathological changes varying from local destruction of the mucosal barrier and underlying tissue (often associated with some degree of inflammation resulting in endothelial lesions), to systemic effects such as blood loss, shock syndrome and even death. Although in most cases immunity develops after repeated infections, the infection leads to economic losses resulting from drop in egg production or malabsorption (poor ∗ Corresponding author. Tel.: +31-485-587370; fax: +31-485-587339. E-mail address: [email protected] (A.N. Vermeulen).
0304-4017/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 4 0 1 7 ( 0 1 ) 0 0 4 7 9 - 4
14
A.N. Vermeulen et al. / Veterinary Parasitology 100 (2001) 13–20
weight gains or feed conversion), even in the absence of clinical symptoms (sub-clinical coccidiosis). Williams (1999) recently estimated that losses due to coccidiosis in chicken industry in 1995 were approximately 40 million pounds Sterling on a production of 625 million broilers in UK. An important aspect in this estimation was that only 17.5% of these were attributed to the costs of prophylaxis and treatment, and around 80% due to losses on feed conversion and weight gain in the presence of drug-treatment strategies. One has to conclude that especially in the broiler industry, there is a need for new strategic concepts to control coccidiosis. Here we review various aspects that contribute to the development of coccidiosis, and ways to control this disease, with an emphasis on the use of vaccines.
2. Factors affecting the outcome of infection 2.1. Age Resistance to Eimeria infection is often age-related. In the field of chicken coccidiosis young animals are generally considered as less susceptible, although the parasite infects the chickens the damage done is often limited (Voeten et al., 1988; Ruff, 1993). 2.2. Genetic background Proliferation of the parasites, severity of lesions and effects on weight gain are very much determined by the genetic background of the host (Long, 1970), possibly related to the potential to develop immunity to infection (Clare et al., 1985). Jeffers and Shirley (1982) concluded that such resistance is mainly caused by the total of the genetic background resulting from the combination of genomes from diverse breeds and not so much by inheritance of one or more specific ‘resistance’ genes. Furthermore, it was demonstrated that inbred lines of White Leghorns selected for resistance to a specific Eimeria species were sometimes more susceptible to another species (Bumstead and Millard, 1992). 2.3. Concurrent infections Besides the genetic factors playing a role in the final outcome of the infection, interference of simultaneous infection with different Eimeria species and interactions with other pathogens such as viruses and enteric bacteria can determine the severity of the disease. Interactions have been shown for Reovirus, Marek’s Disease Virus, Newcastle Disease Virus and Infectious Bronchitis Virus, mostly aggravating the symptoms of both infections (Ruff, 1993). Managerial factors, like poor hygiene, presence of other animals on the farm, the use of in-feed medication and the occurrence of other infectious diseases in the present or previous flock all affect the spread of the disease and the severity of the infection (Graat et al., 1998). For instance, increasing problems associated with concurrent infections of Eimeria and Clostridium perfringens or E. coli have been reported, especially in Nordic countries where antibiotics are banned from use in broiler management (Van der Stroom and van der Sluis, 1999).
A.N. Vermeulen et al. / Veterinary Parasitology 100 (2001) 13–20
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3. Control strategies 3.1. In-feed prophylactic medication Reduction of infection pressure is the first measure to control coccidiosis outbreaks. Cleaning of the broiler house between consecutive rounds is important, but some infective oocysts will survive any practical cleaning procedure. If left untreated infection will gradually build up in the flock during the growing period and can cause coccidiosis in chickens that have developed no or only partial immunity. To reduce the risk of contracting an infection, prophylactic ‘in-feed’ medication is being used with considerable success. However, the abundant use of anti-coccidials has resulted in the selection for drug resistant strains, which has reduced the efficacy of many of the currently used coccidiostats (Chapman, 1993, 1999; Vertommen et al., 1990). As in many countries legislation prohibits the use of medication until slaughter, withdrawal periods of the medication have been imposed, which further increases the risk of developing infection at the end of the growing period. Thus, when coccidiostats are used to control coccidiosis, the risk for coccidiosis to develop in a flock gradually increases with age (increase of infection pressure) with maximal risk during the withdrawal period. To further limit selection of drug-resistant strains, shuttle and rotation programs have been introduced in which different coccidiostats are alternately used, either within a single flock or in a series of consecutive flocks. 3.2. Vaccination When chickens are infected with low numbers of Eimeria parasites, protective immunity is induced after two to three consecutive infections (Joyner and Norton, 1973; Long et al., 1986). All commercially available coccidiosis vaccines are based on this principle (Table 1). Depending on the characteristics of the vaccine strains used, these vaccines can be roughly divided in three groups. Table 1 Commercially available vaccines against chicken coccidiosis Trade name
Attenuated
Ionophore tolerance
Speciesa
Applicationb
Manufacturer
Coccivac D Coccivac B Immucox C1 Immucox C2 Paracox Paracox 5 Livacox D Livacox T Nobilis COX ATM
No No No No Yes Yes Yes Yes No
No No No No No No No No Yes
A, T, M, N, B, P, H, Miv A, T, M, Miv A, T, M, N A, T, M, N, B, Mi, P A, T, M2, N, B, Mi, P A, T, M2, Mi A, T A, T, M A, T, M2
DW DW/SB DW/G DW DW SF DW DW DW/SB
Schering plough Schering plough Vetech labs Vetech labs Schering plough Schering plough Biopharm Biopharm Intervet
a Species: E. acervulina (A), E. tenella (T), E. maxima (M), E. necatrix (N), E. brunetti (B), E. mitis (Mi), E. mivati (Miv), E. hagani (H), E. praecox (P). M2 means two antigenically different strains of E. maxima. b Applications: drinking water (DW), spray on birds (SB), spray on feed (SF), oral gel (G).
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3.2.1. Live, virulent strains These vaccines comprise a variable number of wild type strains depending on their formulation and field of application (Lee, 1987). For broiler-breeders up to eight Eimeria species are included in these products (Coccivac® D, Immucox® C2). For use in the broiler industry this number is restricted to up to four species (Coccivac® B, Immucox® C1). 3.2.2. Live, attenuated strains Attenuated lines of Eimeria parasites can be obtained by repeated selection for early maturation (pre-cociousness) or serial passage through embryonated eggs (TA lines) (Long, 1972; Jeffers, 1975). The most important feature of these lines is their reduced proliferative capacity resulting in less damage to the intestinal lining after one passage through the gut. This has led to the development of two attenuated vaccines, Paracox® (precocious strains; Shirley and Millard, 1986; Shirley, 1989; Williams, 1992) and Livacox® (precocious and TA strains; Bedrnik, 1989). As with the live virulent vaccines, here vaccines have been developed for different markets. Live vaccines (with either virulent or attenuated parasites) are given to chickens in the first week of age, which results in early low-level infection followed by cycling of the vaccine parasites through the litter and induction of immunity against a heavy field challenge. Any use of therapeutics or feed additives that interfere with Eimeria development cannot be used during the period of development of immunity. Thus, when vaccination is used to control coccidiosis the risk of contracting coccidiosis is highest at the early age (weeks 1–3), and decreases as immunity has developed (from weeks 3 to 4 onwards). 3.2.3. Live, tolerant to ionophores A new development has been the use of live Eimeria strains that are relatively tolerant to ionophores. An experimental vaccine comprising a strain of E. acervulina and a strain from E. maxima, both of which were partially tolerant to salinomycin, has been used in USA (Danforth, 2000). A live vaccine that can be used with different ionophores has been recently introduced (Nobilis® COX ATM, Table 1) to the market (Schetters et al., 1999). The vaccine comprises strains of three different Eimeria species (E. acervulina, E. tenella, and E. maxima) which are relatively tolerant to ionophores. As with all the vaccines described above, the risk of contracting coccidiosis is minimal after the animals have developed immunity (3–4 weeks). The advantage of these specific vaccines is that they allow the use of ionophores during the first 3–4 weeks when immunity is not complete. Such use limits the increase of infection pressure due to expanding field strains during the period of development of immunity, which further reduces the overall risk of contracting coccidiosis.
4. Factors affecting efficacy of commercially available vaccines 4.1. Route of administration Crucial to the efficient induction of protective immunity using live vaccines is the even distribution of the vaccine oocysts over the animals. As the vaccines are oral vaccines,
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administration through drinking water, and a variety of feed-based administrations have been used. The little data that are available about use in broiler flocks indicate that performance of vaccinated flocks is generally not improved over medicated flocks (Williams et al., 1999; Waldenstedt et al., 1999). Overall data even showed higher feed conversions in vaccinated over medicated flocks. This could be due to the fact that these routes of administration rely upon the initiative of the individual chicken to receive a full dose of vaccine. The hierarchy in a specific flock will affect the distribution of the vaccine over the individual animals; some receiving more than one dose, others receiving no vaccine at all. This situation is less likely to occur when the vaccine is sprayed onto the birds. Part of the vaccine will be taken up through the eyes, and part through the beak when chickens arrange their feathers. It is for this reason that spray vaccination onto the birds has recently been recommended, and the available data show that over 94% of animals vaccinated by spray had indeed taken up oocysts (Schetters et al., 1999). 4.2. Compatibility with broiler production management When administered correctly to the chickens, all available vaccines induce immunity in 3–4 weeks. However, the performance of the vaccinated chickens should (depending on the field infection pressure) be equal to or better than that of medicated non-vaccinated birds. Danforth (1998) described several trials performed on farms, throughout the USA, investigating the practical aspects of different large-scale vaccination strategies and especially parameters determining the efficacy of these vaccines. These studies demonstrated that most broiler breeds exhibited a transient slight drop in weight gain after vaccination, but recovered quickly and compensated for the loss after 3 or 4 weeks. In another series of field experiments it was shown that vaccinated flocks had higher feed conversion rates than non-vaccinated but medicated flocks (Williams et al., 1999). The improvement of feed conversion by 4% in the absence of coccidial challenge has been widely recognized for drugs such as salinomycin or maduramycin (Radu et al., 1987). One of the most interesting observations was that the combination of such ionophore treatment with vaccination could further improve the effect of vaccination or treatment alone. Data from field trials with a vaccine that could be used with ionophores support this observation (Table 2). Table 2 Performance data of the trial 1 vaccinated and historic control flocks
Nobilis COX ATM Number of broilers placed Total mortality (%) Growing period (days) Average slaughter weight (g) Average growth per day (g) Feed conversion Feed conversion 1500a European production index a
Post-trial flock
Trial flock
Pre-trial flock 1
Pre-trial flock 2
No 19500 3.3 44 2008 45.6 1.83 1.63 240
Yes 19225 3.6 44 2097 47.7 1.79 1.55 257
No 19000 4.2 45 1999 44.4 1.81 1.61 234
No 19000 9.2 43 1918 44.6 1.83 1.66 221
Standardized for 1500 g body weight.
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5. Future control of coccidiosis Live coccidiosis vaccines will be used as an aid in the control of coccidiosis in broilers. Furthermore, the possibility of ovo application (at the hatchery) which has become the method of choice for live virus vaccination in the USA (Gagic et al., 1999) remains an area of interest to improve efficacy of vaccination. Although it has been shown that sporocysts can be injected directly into the yolk sac (Dibner et al., 1999) this method seems less likely to become general practice. The development of sub-unit and recombinant vector-vaccines is being pursued (reviewed in Vermeulen, 1997; Jenkins, 1997). These strategies have the advantage that no live parasites are introduced, and the vectors used are safe and often already used in vaccines. Moreover, it is expected that immunity against the vector-organism is also induced, which is for carriers such as HVT or Salmonella certainly an advantage. Recent data from our lab show the potential of recombinant vaccines. Two different vectors (i.e. attenuated Salmonella typhimurium and herpes virus of turkeys (HVT)) were used to make constructs that expressed different antigens of each of the three Eimeria species: E. acervulina, E. tenella and E. maxima. Broilers were vaccinated at 1 day of age and challenged 2 weeks later with a mixture of oocysts of E. tenella, E. acervulina and E. maxima. Three weeks after challenge infection the vaccinated animals had significantly higher body weight than the non-vaccinated control animals. In addition, feed conversions of all vaccinated groups were over five points better than the control group (Table 3). This experiment is an example of the potency of these kinds of vaccine in the future control of coccidiosis. Broiler producers are faced with changes in public appreciation of their product. In the northern Hemisphere there is an increased demand for biological products that have been produced in a less industrialized environment. Furthermore, increased awareness of the consequences of the use of antibiotics will divert the market towards broilers that have been produced with a minimal of feed additives and antibiotics. This change in public attitude will be reflected in legislation which producers will have to comply with. Producers will have to look for alternative control measures as problems may be expected. For instance, reduction of the use of antibiotics in Sweden was associated with an increase in the incidence of necrotic enteritis (caused by Clostridium perfringens) and Escherichia coli-caused syndromes (Van der Stroom and van der Sluis, 1999). Similarly, it is envisaged that a reduction Table 3 Effect of vaccination of broiler chickens at 1 day of age with different recombinant vaccine preparation on performance after challenge infection with a mixture of E. acervulina, E. tenella and E. maxima oocystsa Treatment
Weight (g)
Feed conversion
Not treated HVT-Eim5 Salmonella-Eim5 Combi HVT/Sal Eim5
1871 ± 210 1960 ± 213∗ 1975 ± 233∗ 2036 ± 160∗
1.80 1.74 1.75 1.74
a Data represent the mean body weight and feed conversion rate (adjusted to 1500 g) at 35 days of age (3 weeks post-infection). HVT: Herpes virus of turkeys; Eim5: combination vaccine with two antigens of E. acervulina, two antigens of E. maxima, and one antigen of E. tenella. ∗ P < 0.05 different from not-treated group.
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of the use of coccidiostats will increase the risk of coccidiosis outbreaks, and it is thus expected that there will be an increased request for effective vaccines. In general, management and nutrition factors will be further improved to minimize losses due to infectious diseases. The use of immunostimulants, betaine and feeds with optimal structural characteristics will be further explored as an aid in the control of coccidiosis (Langhout, 1999). Concluding, it has become clear that the poultry production is changing both in terms of volume as well as in structure. The massive in-feed medication as has been used for antibiotics will be replaced by other means to control infectious diseases. Vaccination is clearly the best long-term solution for the problems that are looming. Improvement of the physiological and thus also immunological fitness of the animal by better hygiene management and using specific feed supplements will certainly complement this approach.
Acknowledgements We are greatly indebted to the technical staff of our laboratory for their assistance to the complicated and laborious experiments reported in this review. We like to thank especially Hay Janssen, and Drs. Goossen van den Bosch, Egbert Hanenberg and Dorothee Paeffgen for their scientific input and comments on this manuscript. References Bedrnik, P., 1989. The role of different Eimeria species in a prospective coccidiosis vaccine. In: Yvoré, P. (Ed.), Coccidia and Intestinal Coccidiomorphs. INRA, Tours, France, pp. 667–670. Bumstead, N., Millard, B.J., 1992. Variation in susceptibility of inbred lines of chickens to seven species of Eimeria. Parasitology 104, 407–413. Chapman, H.D., 1993. Twenty-one years of Monensin for the control of coccidiosis. In: Barta, J.R., Fernando, M.A. (Eds.), Proceedings of the 5th International Coccidiosis Conference, Guelph, Canada, pp. 37–45. Chapman, H.D., 1999. The development of immunity to Eimeria species in broilers given anticoccidial drugs. Avian Pathol. 28 (2), 155–162. Clare, R.A., Strout, R.G., Taylor Jr., R.L., Collins, W.M., Briles, W.E., 1985. Major histocompatibility (B) complex effects on acquired immunity to cecal coccidiosis. Immunogenetics 22, 593–599. Danforth, H.D., 1998. Use of live oocyst vaccines in the control of avian coccidiosis: experimental studies and field trials. Int. J. Parasitol. 28, 1099–1109. Danforth, H.D., 2000. Increase in anticoccidial sensitivity seen after field trial studies with five oocyst vaccination of partially drug-resistant strains of avian Eimeria species (abstract). In: Proceedings of the 75th Annual Meeting of the American Society of Parasitologists and the 53rd Annual Meeting of Protozoologists, p. 90. Dibner, J., Ivey, F.J., Knight, C.D., 1999. Direct delivery of live coccidiosis vaccine into the hatchling yolk sac. In: van der Sluis, W. (Ed.), World Poultry. Elsevier, Amsterdam, pp. 25–26. Gagic, M., St Hill, C.A., Sharma, J.M., 1999. In ovo vaccination of specific-pathogen-free chickens with vaccines containing multiple agents. Avian Dis. 43 (2), 293–301. Graat, E.A., van der Kooij, E., Frankena, K., Henken, A.M., Smeets, J.F., Hekerman, M.T., 1998. Quantifying risk factors of coccidiosis in broilers using on-farm data based on a veterinary practice. Prev. Vet. Med. 33 (1–4), 297–308. Jeffers, T.K., 1975. Attenuation of Eimeria tenella through selection for pre-cociousness. J. Parasitol. 61, 1083– 1090. Jeffers, T.K., Shirley, M.W., 1982. Genetics, specific and infraspecific variation. In: Long, P.L. (Ed.), The Biology of the Coccidia. University Park Press, USA, pp. 63–100.
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