Thermostable Newcastle Disease Vaccines

Robust vaccines are required to protect village chickens against Newcastle disease. Thermostable vaccines derived from avirulent Australian strains of Newcastle disease virus (strains V4 and I-2) have proved successful for this purpose. These vaccines have been developed through ACIAR projects and have been adopted by other international aid agencies. It is now possible to offer integrated workshops in which administrators and field workers are trained in the use of thermostable vaccines, poultry-specific extension activities and gender aspects of poultry production. At the same time, laboratory workers are taught the skills required to produce and test thermostable vaccine on a small scale, and to assure the quality of the product. Vaccine seed material is supplied without cost. Recent events in Australia have led to some concern among potential users of the vaccine. Virulent strains of Newcastle disease virus have apparently risen from the avirulent strains that have been circulating in Australia for at least 30 years. Some have suggested that the virulent strains of Newcastle disease virus first recognised in 1926 were derived by a series of mutations from pre-existing avirulent viruses. The virulence of strains of Newcastle disease virus is currently judged by the sequence of amino acids at the cleavage site of the viral fusion (F) protein. Work in several laboratories has indicated that the sequences in V4 and I-2 are similar to those in other mild vaccine strains. One mesogenic vaccine strain used in developing countries has the same sequences as velogenic viruses. It is also argued that the Australian ‘virulent’ viruses do not produce a disease with high mortality and would be insignificant pathogens compared with Newcastle disease viruses that circulate in Africa and Asia. Thermostable Newcastle disease vaccines, locally produced and widely distributed, would allow village chickens to contribute fully to alleviating poverty and improving nutrition in rural areas. Suitable systems of extension and cost recovery would make the enterprise sustainable. MOST people attending this meeting would agree that village chickens are a very important resource for populations in rural and peri-urban areas in developing countries. Most would agree that village flocks are not managed to produce at their full potential. In most cases, the major constraint to enhanced productivity is the viral disease known as Newcastle disease, which devastates poultry populations in developing countries. Commercial vaccines and attention to biosecurity are important steps in the control of Newcastle disease in commercial chickens. Only over the past 10 or 15 years have we been able to contemplate the control of Newcastle disease in village chickens. The key has been the production of vaccines that are cheaper, less complex and more robust than commercial Newcastle disease vaccines. The problems have been many. The flocks are small, scattered and multi-aged. The owners of the chickens (often women) lack economic or political influence, and veterinary and extension services are seldom responsive to their needs. Commercial vaccines are not suitable for use in resource-poor villages. Individual vials contain at least 1000 doses (economies of scale), the vaccines are heat-labile and require continuous refrigerated storage and if imported they are a drain on foreign exchange. The author believes that these problems can be overcome, and bases this assertion on his experience with control of Newcastle disease since 1984. In many places, it is not yet feasible to construct cold chains to link vaccine producers to village flocks, so thermostable vaccines are required. Not all the chickens can be caught readily for vaccination, so 1 Emeritus Professor Peter Spradbrow, AM, Division of Veterinary Pathology and Anatomy, University of Queensland, PO Box 125, Kenmore, Brisbane 4069 Australia.