Improved diagnosis and control of infectious coryza in China and Australia

• Institute of Animal Husbandry and Veterinary Science, China

The disease - an upper respiratory tract infection - usually affects most birds in a flock, but kills few. However, infected birds eat less, experience retarded growth, egg production drops, and birds become susceptible to other diseases.

Although coryza is widespread in poultry in China, specific types of the bacterium are not recognised, and vaccines based on occasional field isolates or imported laboratory strains are unlikely to provide good protection against pathogenic Chinese strains.

In Australia, scientists are aware of the types of H. paragallinarum in local poultry, and effective vaccines. However, there is no serological test available to monitor the efficacy of vaccination programs. Vaccine batches need testing in challenge trials requiring an alternative to conventional culture techniques, such as a DNA probe. Although most laboratories can isolate Haemophilus spp. from birds, only the Animal Research Institute in Brisbane can provide confirmatory identification of H. paragallinarum and serotyping.

Infectious coryza, a disease of poultry that is economically significant to developed and developing countries, lacks specific techniques and knowledge to diagnose and prevent its spread.

Chickens are second to pigs as a source of protein in China, consquently, the Government places high priority on combating poultry diseases. Scientists at the Institute of Animal Husbandry and Veterinary Science have been investigating infectious coryza since 1987.

The high cell counts necessary for efficacy in vaccine production are difficult to achieve, owing to lack of knowledge of the optimal growth conditions for the bacterium Haemophilus paragallinarum. Fermentation technology could improve the cell yield.

This project has three main objectives:

. to develop sensitive and serovar-specific serological tests based on ELISA methodology utilising monoclonal antibodies;
. to develop a simple, non-isotopic DNA probe to replace the technically difficult and slow conventional culture; and
. to apply modern fermentation technology to the production of antigen for infectious coryza vaccines.

Scientists working in infectious coryza research have been involved in a number of international collaborative projects on the disease and have led industry-funded projects on vaccine development and new serotyping methods for H. paragallinarum. Whole-cell proteins have been characterised as well as outer membrane proteins and plasmids of the organism. In collaboration with field staff, the value of molecular finger-printing techniques in understanding the epidemiology of infectious coryza has been demonstrated.

Much of the experimental work will be carried out at ARI in Australia in years 1 and 2 of the project. The final 2 years will be spent implementing the new techniques in China.

The DNA probe will be used on materials submitted from local outbreaks of infectious coryza and the production of vaccines based on fermentation technology developed in Australia will begin.