Fowl choleraa devastating disease of domestic chickens caused by a number of strains of Pasteurella multocidais second after Newcastle disease in causing chicken deaths in Asia. In the Philippines, village chickens are the worst affected; in Sri Lanka, chickens in commercial flocks.
The disease also causes significant losses in Africa and in the intensive poultry industries of the developed countries. Current vaccines give poor protection and are effective only against the same (homologous) strain of Pasteurella used to make the vaccine.
This project stems from the successful ACIAR project on the development of Newcastle disease vaccines for village poultry in Asia. Researchers engaged in the Australian, Sri Lankan and Philippine aspects of the Newcastle disease project will build on the collaboration they established between the countries in the first project to develop improved vaccines for fowl cholera. They will be joined by Dr Alan Frost, a specialist on bacterial diseases from the Department of Veterinary Pathology, University of Queensland.
While bacteria possessing virulence traits are required for vaccine production, it seems that virulent strains of Pasteurella, when cultured in laboratory media available at present, fail to express chemical factors that are essential for disease (and antibody) production.
The team believes there is potential for improving fowl cholera vaccines by identifying an additive (e.g. a suitable chicken extract) that will allow Pasteurella grown in culture medium to retain the virulence characteristics of the bacteria that grow in diseased chickens. Such bacteria could then be grown in bulk for vaccine manufacture. The chances of success are excellent. It is already known that Pasteurella bacteria derived directly from the tissues of affected birds are cross-protective, while bacteria cultured using currently available techniques produce only homologous protection.
The researchers will isolate virulent bacteria from the blood of diseased chickens and collect antibodies from the serum of birds that recover from the disease. They will use the modern technique of Western blotting to characterise the antigens that produce an effective immune response; and they will identify virulence antigens shared between strains of P. multocida with the aim of producing vaccines that will give adequate protection against homologous and heterologous strains.
The team aims to produce two types of broadly protective vaccine:
. an effective and economical killed vaccine that can be administered easily under any conditions of husbandry; and
. an oral live vaccine, for spreading through chicken populations under village conditions.
Research to be carried out in the three countries includes:
. investigation of growth factors that alter the surfaces of Pasteurella bacteria;
. development of Western blotting to determine the surface antigens to which chickens react;
. development of a system to measure protective antibody, using passive protection of chicken embryos;
. investigation of various inactivating agents and adjuvants to maximise production of protective antibody; and
. development of attenuated vaccines using aromatic-dependent mutants or heat-resistant mutants.
. production of large quantities of vaccine from local strains using growth factors identified in Australia for retaining virulence;
. investigation of methods of inactivation and of different adjuvants; and
. protection trials with killed vaccines, using local virulent strains for challenge.
. production of aromatic-dependent mutants or heat-resistant mutants from local strains, or importation of Australian strains;
. investigation under laboratory conditions of various methods of applying the vaccine; and
. protection trials with attenuated vaccines, using local virulent strains for challenge.
As fowl cholera is a problem in all Asian countries, successful vaccines that can be manufactured locally will benefit poultry producers over a wide geographic area. Village chicken growers will benefit most from the project, whether they breed the traditional scavenging birds or keep commercial poultry in small numbers. Commercial breeders will benefit to a lesser extent because they already have access to moderately efficient vaccines and to antibiotics. A single, broadly cross-reactive vaccine will also benefit the Australian industry by replacing homologous vaccines for use in both laying and breeder flocks. In addition, it could lead to export markets for Australian-produced vaccine.