Progress in control of hydatidosis using vaccination--a review of formulation and delivery of the vaccine and recommendations for practical use in control programmes.
A vaccine to protect sheep, goats, and bovines against hydatid disease caused by the cysts of Echinococcus granulosus is prepared as a recombinant fusion protein expressed in Escherichia coli. Solubilised inclusion bodies are injected, together with Quil A, subcutaneously on two occasions 1 month or more apart, and induce protection against infection which lasts for at least 12 months. A third injection given 6-12 months after the second injection induces a high and long-lasting protection against artificial or natural challenge infections. This review describes work carried out on the formulation, safety and efficacy of the vaccine under laboratory and field conditions, using artificial or natural challenges with E. granulosus eggs, followed by necropsy. Hydatid control programmes based on regular treatment of all dogs with the correct dose of a highly-efficient anthelmintic have sometimes not been successful in Continental environments. Access to dogs is difficult in summer because of the distances to summer pastures, and is often impossible in winter because of snow. A control program using strategic twice-yearly anthelmintic treatment of dogs is likely to be successful provided grazing animals are vaccinated as well. Vaccination as a control tool only requires the veterinarians to visit two times a year, and while the veterinarian is present, the dogs can be treated with anthelmintic for little additional cost. One visit should take place after the autumn kill of animals for winter consumption, and this is a good time to vaccinate animals born in the summer, and also all other animals while they are healthy and immunologically responsive. The other visit should take place in the spring, at which time animals born during winter can be vaccinated. Although a single immunization has been shown to induce a useful degree of protection, where possible it is best to give two initial injections, 1 month apart. If it is possible for veterinarians to stay in the field for 2 months in November/December and March/April, in order to give the two injections, a more rapid onset of full protective immunity will initially be achieved than if the injections are given 6 months apart. A large-scale safety and efficacy trial involving 50,000 and 100,000 lambs in Qinghai and Xinjiang Provinces of China has taken place. Results have confirmed safety and efficacy. In most countries, prevalence of infection increases with age. The vaccine has no effect on established cysts, and therefore, in order to prevent the biomass of Echinococcus spp. from increasing, it might be an effective strategy to begin a control programme by vaccinating all animals. Because many of the older stock will already be infected, they will remain a source of infection for dogs for the average lifetime of the stock. Dogs will still be able to be infected from the older stock, and will continue to infect humans. We advocate that a vaccination programme be accompanied by education about hydatid disease, and anthelmintic treatment of dogs in late autumn and early spring.
Heath
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AgResearch, Wallaceville Animal Research Centre, PO Box 40063, Upper Hutt, New Zealand. hidatidosis@coopsar.com.ar
Jensen
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Lightowlers
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D000818:Animals; D002417:Cattle; D002626:Chemistry, Pharmaceutical; D003362:Cost-Benefit Analysis; D004283:Dog Diseases / Q000188:drug therapy / Q000517:prevention & control; D004285:Dogs; D016503:Drug Delivery Systems; D004443:Echinococcosis / Q000191:economics / Q000517:prevention & control / Q000662:veterinary*; D006801:Humans; D007112:Immunity, Maternally-Acquired; D010270:Parasite Egg Count; D012756:Sheep; D012757:Sheep Diseases / Q000517:prevention & control; D014611:Vaccination / Q000662:veterinary*; D014612:Vaccines / Q000008:administration & dosage / Q000009:adverse effects / Q000276:immunology
D014612:Vaccines