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Tracking Down Newcastle VirusBy Sharon Durham
October 19, 1999
How can you distinguish a Newcastle virus that would give a chicken a "cold" from one that could lead to destruction of entire flocks and bans on U.S. poultry imports?
To find out, scientists at USDA's Agricultural Research Service have devised a dual strategy: genetic codebreaking and clinical tests. Native Newcastle strains cause only mild symptoms. But the researchers and their USDA colleagues face a continuous challenge of distinguishing weak Newcastle strains from virulent, exotic, scary ones. At ARS' Southeast Poultry Research Laboratory in Athens, Ga., microbiologist Bruce Seal examines Newcastle gene sequences and veterinarian Daniel King evaluates how the viruses affect birds.
About 12 million chickens and other poultry were destroyed to eradicate a 1971 Newcastle outbreak in California. The disease was transmitted from infected imported parrots. USDA's Animal and Plant Health Inspection Service established quarantine stations to stop infected pet birds from entering the country.
But that isn't enough, because viruses can fly over borders. The first known die-off of wild water birds from Newcastle disease in the U.S. occurred in 1992. Hundreds of migrating cormorants died at a North Dakota lake. Soon, 26,000 turkeys were destroyed to halt the outbreak. In Athens, Seal compared viral genes and confirmed that the cormorants were the source.
When an anhinga--a native wild water bird--died from Newcastle disease in a Florida theme park in 1993, an APHIS microbiologist sent a virus sample to Athens for a more intensive look at its potential virulence. Seal discovered it was genetically almost identical to the killer North Dakota strain. But King's clinical studies showed it only moderately virulent.
ARS and APHIS will continue keeping an eye on the anhinga strain and other Newcastle isolates to provide an early warning system to the poultry industry. A story about the research appears in October's Agricultural Research magazine and online at: