Newcastle Disease: Protecting Poultry
Farmers on Two Fronts
Veterinary medical officer Jack King inspects embryonated chicken eggs before
inoculation. After the shell surface is disinfected with iodine, a small hole
will be punched to allow entry of a needle.
Newcastle disease has plagued poultry producers for 75 years. Strains native
to the United States cause only mild symptomsakin to a "common
cold" for poultry. But exotic strains can cause devastating losses in
other countriesand in the United States, if they invade via smuggled
birds or wild birds, such as cormorants.
Keeping tabs on hazardous forms of Newcastle disease is a responsibility of
USDA's Animal and Plant Health Inspection Service, which collaborates closely
with the Agricultural Research Service.
Newcastle disease surfaced in this country in the 1930s. By the late 1940s,
scientists had developed vaccines. They had also identified virus strains that
produced symptoms in poultry ranging from mild to fatal. But identifying the
differences in virus strains that explain their differing severity remains a
At ARS' Southeast Poultry Research Laboratory in Athens, Georgia,
veterinarian Daniel J. King and microbiologist Bruce S. Seal work to keep U.S.
poultry farmers protected on two fronts. Seal studies the genetic component of
Newcastle virus samples sent in by APHIS. King studies how these viruses sicken
and kill birds.
"Ultimately," says King, "we hope this combined approach will
lead to better detection methods, so live birds don't have to be used to
identify the virulence, or disease-causing ability, of new strains."
During 1971, a particularly nasty Newcastle strain from pet birds struck the
poultry industry in California. Eradication took over 2 years and cost $56
million in federal funds. Nearly 12 million birds had to be destroyed.
In Seal's lab, analyses of gene sequences within the last few years helped
confirm scientists' long-suspected connection between this outbreak and
infected imported parrots. Some birdsparticularly in the parrot
familycan appear healthy even while harboring a virulent Newcastle
Microbiologist Bruce Seal and technician Joyce Bennett prepare samples from new
for the automated nucleic acid sequencer. Data obtained will be used to compare
the new isolates with data from previous ones deposited in the Genbank
After the California outbreak, APHIS established quarantine stations to stop
infected pet birds from entering the country.
The stations and other APHIS actions have protected U.S. poultry, despite
ever-present threats. Virulent Newcastle strains have been detected in U.S. pet
bird populations in all but 3 years since 1974. In addition, virulent Newcastle
virus periodically flares up in other countries. In 1998, Australia began
battling a virulent strain that apparently evolved from a weak virus indigenous
to Australian poultry for at least 30 years.
Meanwhile, making sure all of America's pet parrots are "born in the
USA" won't remove Newcastle's threat to this country. Wild birds can also
carry strains deadly to poultry.
In 1992, 26,000 turkeys in North Dakota were destroyed after APHIS diagnosed
virulent Newcastle disease in the flock. Cormorants were the suspected source.
Hundreds had died from the disease at a lake near where the turkeys were being
reared on range. Seal confirmed this suspicion when he compared the genomes of
turkey and cormorant isolates.
The episode was part of the United States' first known Newcastle-related
die-off of free-ranging wild birds.
Besides directly threatening U.S. poultry, Newcastle can damage our export
markets. In 1998, several dead and dying game chickens from a backyard flock in
California's Central Valley were delivered by the owner to the California
Veterinary Diagnostic Laboratory in Fresno. APHIS' National Veterinary Services
Laboratories in Ames, Iowa, confirmed the birds were infected with exotic
In accordance with international trade law, the incident was reported to the
Office of International Epizootic Diseases in Paris, France. Some countries
instituted a temporary ban on imports from the region until the outbreak was
eradicated. The ban cost area poultry producers hundreds of thousands of
"Newcastle disease may not be a household word," says King.
"But you can see why it's a big concern to the poultry industry. Each time
APHIS sends us a strain with unique characteristics, we can understand the
A recent case illustrates how this partnership works.
In 1993, an anhingaa wild water bird native to the Southeastwas
found dead among a captive population in a Florida theme park. Samples from the
bird were sent to APHIS microbiologist Dennis Senne in Ames. He confirmed the
virus was Newcastle.
Senne also evaluated the strain's potential virulence, using a standard test
that determines how quickly a strain kills chicken embryos. The result: While
the strain was not extremely virulent, neither was it as weak as a common cold.
Senne then sent a sample to King.
"Our job is basic diagnosis," Senne says. "But we often see
isolates that come from interesting sources or seem unusual in their ability to
cause disease. On the front lines, we don't have time to study these samples in
detail. We rely on Jack King, Bruce Seal, and others to tell us where these
different strains might be coming from and what kind of threat they might
Senne's samples of anhinga virus arrived at the Athens laboratory by
overnight express. Seal discovered that the anhinga isolate appeared almost
identical to the one that killed the North Dakota turkeys. But while the
genetic code was potentially ominous, King found that the anhinga strain's
virulence was only moderate.
The ARS scientists deposited the anhinga strain's genetic code into
international databases, such as Genbank, designed for accumulating nucleic
acid sequences. Through the databases, researchers worldwide can quickly share
new genetic information when viral samples are not available.
"The anhinga case demonstrates the value of our two-step
approach," says King. "The genetic coding alone, or the clinical
study alone, is not enough. We can know more about what a virus can do by
joining the two approachesthe molecular and the clinical."
That approach continues in studies of new isolates from domestic poultry,
imported doves, pheasants, and other birds.By Jill Lee,
formerly with ARS.
This research is part of Animal Health, an ARS National Program (#103)
described on the World Wide Web at
Daniel J. King and
Bruce S. Seal are with the USDA-ARS
Poultry Research Laboratory, 934 College Station Rd., Athens, GA 30605;
phone (706) 546-3434, fax (706) 546-3161.
"Newcastle Disease: Protecting Poultry Farmers on Two
Fronts" was published in the October 1999 issue of Agricultural