...From the pages of Agricultural Research magazine
A New, Rapid Test for Avian Influenza
David Suarez, veterinary
medical officer, and Suzanne
DeBlois, biological science
laboratory technician, prepare
to load chicken tracheal swab
samples into a real-time
Avian influenza is a vexing problem for poultry producers
in the United States. One strain of the virus that causes the disease,
H7N2, has been endemic in live-bird markets in the Northeast and Florida
since 1994. These markets sell a broad variety of live poultry, often
to specific ethnic markets. Consumers can choose either at-home or in-shop
preparation of the bird.
Unfortunately, live-bird markets also serve as central
mixing areas for avian influenza viruses and can harbor them for a long
time. These markets can act as reservoirs from which viruses can potentially
spread to larger, commercial facilities. Current regulatory efforts
are ineffective in eradicating the virus.
ARS veterinary medical
officer David Suarez has developed a test to quickly identify H7N2 presence
in a flock. It's called an RRT-PCR test, short for real-time, reverse-transcription,
polymerase chain reaction. Suarez's test, using a fluorescent probe,
produces results in less than 3 hours.
Avian influenza infections can range from subclinical
(with no symptoms), to mild (with production losses), to severe (with
high rates of illness and death). The deadly form is called HPAI, short
for highly pathogenic avian influenza.
"It can be difficult to identify the mild form because
it is hard to differentiate it from other, more pedestrian health problems
the flock exhibits," said Suarez, who is in the Poultry Disease
Research Unit, in Athens, Georgia.
Suarez's test uses the virus's genetic code to identify
it. The gene that identifies H7N2 avian influenza virus is the hemagglutinin
gene. It's a rapidly evolving gene that has a high rate of amino acid
substitutions, which may seem small in the grand scheme of the virus's
genome. But each substitution moves the virus from a mildly pathogenic
strain closer to a highly pathogenic strainone that can kill an
entire flock in as little as a week.
The last HPAI outbreak in the United States occurred in
Pennsylvania in 1983 and 1984. Through combined federal, state, and
industry efforts this outbreak was controlled. But milder avian influenza
viruses were isolated from live-bird markets in several states from
1986 to 1989.
Recently, in Virginia, a mild form of avian influenza
infected 197 flocks, and 4.5 million birds had to be killed to prevent
further spread of the virus. Though the virus remained fairly innocuous,
it had the potential to mutate and become deadly.
The mild-form H7N2 virus has been found in commercial
poultry operations at least three times in the last 5 years, causing
disease and serious economic losses for the industry.
"The costs of the 198384 outbreak were staggering:
$63 million in federal funds and $350 million in increased consumer
costs. This new test may avoid a replay of that devastating scenario
by identifying the viruses earlier and with more accuracy," said
Durham, Agricultural Research Service Information Staff.
This research is part of Animal Health, an ARS National
Program (#103) described on the World Wide Web at http://www.nps.ars.usda.gov.
"A New, Rapid Test for Avian Influenza" was published in the February 2003 issue of Agricultural Research magazine.