Control of Newcastle disease in village chickens with oral V4 vaccine

• Research Institute for Veterinary Science, Indonesia
• Department of Livestock Development, Thailand
• Bureau of Animal Industry, Philippines
• Breeding and Veterinary Department, Burma (Myanmar)
• Veterinary Research Institute, Sri Lanka
• Universiti Pertanian Malaysia, Malaysia

Scavenging village chickens provide an important source of eggs, meat and supplementary income in developing countries throughout the tropics and subtropics, but are not very productive - largely because of high mortality due to uncontrolled Newcastle disease. Velogenic, viscerotropic strains of this virus, endemic throughout Asia, can cause 100% mortality in unvaccinated chickens.

This project builds on the results of Project 8334, which included development of an effective heat-resistant Newcastle disease vaccine for village chickens, based on the avirulent Australian V4 strain of the virus. It is cheap, safe, has a moderate shelf life and spreads readily, and confers substantial protection against challenge with the virulent virus.

Improved cost-effectiveness of vaccine delivery to the chicken remains the major problem. Food pellets coated with V4 virus in the Glatt machine have proved an excellent oral vaccine. However, production from a single Glatt machine is limited and food pellets will not be the ideal carrier in all countries. Scientists in Malaysia will investigate the suitability of this machine for coating other village-based foods (whole or broken grain) and the availability of better protectants than polyvinyl pyrolidone. Those at St Lucia in Australia will look at coating methods that do not rely on the Glatt machine, at the use of dry powder as a vaccine and at inert non-nutrient particles (latex, cellulose or chitins) as carriers.

The Australian team at Armidale will study the interaction between the V4 virus and its host, which remains poorly understood - for example, where does the virus enter the host? Preliminary results at St Lucia have shown some localisation in the crop and it may not be necessary to engineer vaccines that will reach the small intestine. If the scientists can determine the route of spread, it may facilitate transmission of the vaccine. They will also study persistence of V4 in village chickens, which may help to establish the optimum interval between vaccinations. Back-up studies in the village environment will follow these laboratory investigations.

Other tasks identified include improving husbandry and nutrition for the young chick, selective vaccination of young birds and the control of other high-mortality diseases, especially fowl cholera.

Control of Newcastle disease in some Malaysian villages has already been achieved. Now, a large-scale program conducted there will determine whether the success of these pilot projects can be repeated. The Malaysian Veterinary Services Department will distribute vaccine for the program and monitor the results and undertake laboratory checks in Kota Baru. Chickens for experimental challenge will be returned to Universiti Pertanian Malaysia.

The project will also conduct efficacy and pilot village validation trials in other Asian countries and carry out an economic analysis of the results. These trials will repeat those successfully completed in Malaysia, with an additional economic and epidemiological component. If they succeed, control programs could follow. Initial efficacy trials using local chickens, conducted under laboratory conditions, will demonstrate that the V4 virus does confer protection against indigenous velogenic strains. Staff will gain experience with the virus and will undertake the subsequent village trials - involving about 3000 chickens in each country - with greater confidence.

These trials will test the HV4 vaccine to validate its use in village systems in Southeast Asia, and establish the overall requirements for introduction of national control programs in Southeast Asia. Other studies will determine the likely costs and social and economic benefits of such programs, and the likely impact of increased poultry production on overall poultry productivity. Scientists will also look for ways to produce village chickens more efficiently, and the potential impact of increased village poultry production on the commercial sector.

If, as expected, the large-scale Malaysian program and at least some of the pilot trials elsewhere are successful, this simple oral vaccine will be ready for use on a wide scale to protect village chickens in developing countries. Although only tested in Asia, it could produce similar benefits in the Middle East, Africa and the Americas.