Newcastle disease (ND), which can be deadly for domestic and commercial poultry as well as wild bird populations, is a major concern worldwide for the poultry industry. Newcastle disease virus (NDV), which typically affects the respiratory, gastrointestinal and/or nervous system, causes disease in more than 250 species of birds.

Symptoms of ND can include coughing, gasping, diarrhoea, lack of appetite and drooping wings. Severe cases can result in mortality rates that exceed 90 per cent in susceptible chickens. To complicate matters, a quick diagnosis of an ND outbreak may be difficult because it can be confused with a clinically similar disease – avian influenza.

Microbiologist Qingzhong Yu examines recombinant Newcastle disease virus vaccine candidates in infected cells

Commercial poultry producers now use vaccines that protect vaccinated birds from disease but these vaccines do not prevent poultry from becoming infected and carrying virulent NDV or shedding it in their faeces. Infected birds can still spread the disease to healthy, unvaccinated birds.

USDA ARS scientists at the agency's Southeast Poultry Research Laboratory in Athens, Georgia, have developed a new vaccine that reduces mortality and severity of ND symptoms in poultry. The vaccine also decreases the amount of virulent virus shed from birds.

Microbiologist Qingzhong Yu in the ARS Endemic Poultry Viral Disease Research Unit and his colleagues in the ARS Exotic and Emerging Avian Viral Diseases Research Unit used reverse genetics technology to create a new vaccine that replaces a gene in the vaccine with a similar gene from the virulent NDV circulating in the environment today.

Dr Yu explained: "Currently, most vaccines used in the United States are formulated with NDV isolated in the 1940s, which is similar to the virulent NDV circulating at that time. Unfortunately, with time, new NDV strains have emerged that are genetically very different from commonly used vaccine strains.

"We found that when the new vaccine, which contains gene sequences similar to the virulent virus, was used in vaccination studies, the vaccinated birds were protected from disease and shed less of the virulent virus after challenge," he said.

Vaccines have been used for more than 50 years to control ND and are successful in reducing mortality and the severity of symptoms, Dr Yu says. However, ND continues to threaten the commercial poultry industry.

The most recent US outbreak in 2002-2003 affected poultry in several states: Arizona, California, Nevada and Texas. The industry suffered a devastating blow when more than 3.4 million birds had to be destroyed. California alone spent more than $160 million to control the outbreak.

The new vaccine protects birds from ND and reduces virus shedding, which will ultimately decrease the spread of the virulent virus.

Further Reading

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