Towards effective control of infectious bursal disease and infectious bronchitis in poultry

• Harbin Veterinary Research Institute, China

Recent accelerated expansion of the poultry industry in China has highlighted the economic importance of the viral diseases infectious bursal disease (IBD) and infectious bronchitis (IB). In other countries where these diseases have been known for decades, hypervirulent strains of IBD virus, and variant strains of both viruses which reduce the effectiveness of vaccines, are of continuing concern.

It is suspected that similar strains are also present in China, limiting poultry production in small villages and farms. Annual losses from IBD and IB in China are estimated at A$75 m, with IBD accounting for A$50 m and IB for A$25 m.

This project arose following a request to ACIAR from the Harbin Veterinary Research Institute (VRI) for CSIRO to address the problem of IBD and IB in China. Scientists from the Institute had already participated in successful AIDAB and ACIAR projects with their CSIRO counterparts, and were aware of research on IBD and IB being carried out by CSIRO in Australia.

The project is to be managed in three related parts - research on IBD, research on IB, and the communication of research results through annual workshops and the establishment of a laboratory network. Most of the research will be done in China, with CSIRO providing detailed protocols and methods. Australian scientists, working in China with their Chinese counterparts and using Australian reagents and imported viruses, will adapt current diagnostic and vaccine technology to suit Chinese conditions. Chinese scientists will also gain experience by making exchange visits to Australian laboratories.

IBD - a relatively new disease in China - causes significant mortality in growing chickens. Survivors of the initial infection tend to have impaired immunity, which prevents them from responding normally to routine vaccinations and allows them to succumb more easily to subsequent infections. IBD is a particular threat to village poultry because the virus is resistant in the environment and remains to infect successive generations of chickens.

In addition, IBD vaccines have not been very successful in China, most likely because of the presence of different strains of virus. The collaborators will purify strains of IBD virus derived from outbreaks in China and from vaccines to compare the antigenic makeup and virulence of these strains with standard strains. They will also determine the effectiveness of existing vaccines through protection experiments.

Unlike IBD, IB is probably not a new disease in China, but it has become increasing evident because chickens are now raised more intensively. Infection in young chickens exacerbates respiratory problems, retarding growth and development, and can cause death from acute renal failure.

In infected layers, egg production is severely reduced. Both the safety and efficacy of present vaccines are questionable. In the project, strains of IB virus isolated from outbreaks in China will be typed using monoclonal antibodies and sera supplied by CSIRO. Subsequently, serotyping tests and monoclonal antibodies against Chinese strains of IB virus will be developed in China and used for the characterisation of Chinese IB viruses. This work will allow the collaborators to determine the prevalence and degree of variance among IB strains and whether or not new vaccines are required.

As part of the third aspect of the project, the Chinese team at Harbin VRI (selected as the most advanced Institute to lead poultry health research in China in the next decade) will upgrade their functional linkages in poultry health with Chinese Academy of Agricultural Science (CAAS) and Ministry of Agriculture, Animal Health and Fisheries (MAAHF) institutes in six provinces.

These institutes will collaborate in the project by investigating outbreaks and sending virus isolates to VRI, and in turn will benefit from the supply of information and reagents. The institute network will be further reinforced by visits from the Australian team and by participation of staff in annual workshops.

Improved control and prevention of IBD and IB in China will contribute directly to the national food supply and the economic welfare of villagers. Trained and experienced scientists and extension personnel, with the ability to carry out research using modern technology and apply the results, will also be of lasting benefit to the country.

Although both IBD and IB viruses are present in Australian poultry flocks, the Australian strains of IBD virus, and possibly IB virus, are not as pathogenic as those found in some other countries. Benefits will flow to Australia from the opportunity to evaluate - using exotic strains of IB virus not freely available in Australia because of quarantine restrictions - Australian IB virus vaccines and monoclonal antibodies generated against Australian strains. Similarly, evaluation of IBD virus vaccines will benefit Australia by helping scientists prepare for a possible future outbreak of virulent IBD in Australian poultry.