For the Birds: New vaccines protect chickens from avian flu
xinixx
Nathan Seppa
By piggybacking components of strains of avian-influenza virus onto an
existing poultry vaccine, scientists have created experimental vaccines
that can prevent bird flu in chickens, two studies show.
While researchers will need to further test the novel vaccines in large
numbers of fowl and against various subtypes of bird flu, the early
results suggest that widespread vaccination of flocks could stall the
spread of bird flu in animals, says molecular virologist Angela
Römer-Oberdörfer of the Federal Research Institute for Animal Health
in Riems, Germany, who coauthored one of the studies. "Controlling
disease in poultry helps to avoid infection of humans," she says.
Previously developed poultry vaccines against influenza aren't widely
used in the United States because they interfere with screening tests
for ill animals.
Research teams in Germany and the United States each designed a vaccine
using a live but attenuated version of a bird pathogen called Newcastle
virus. They engineered the virus to produce the version of a protein,
called hemagglutinin, that is found on either the bird-flu virus known
as H5N1 or the one called H7N7. Each vaccine prompts the immune system
to produce antibodies against the hemagglutinin and, therefore, against
the virus.
The H5N1 flu has killed or led to the culling of millions of poultry,
mostly in Asia. The H7N7 strain led to the deaths of millions of
chickens in the Netherlands in 2003.
In a series of experiments, the research groups sprayed an aerosol of
the vaccine into chicks' eyes. The animals subsequently fended off
infection after exposure to bird-flu virus, the two groups report in
the May 23 Proceedings of the National Academy of Sciences. In both
studies, unvaccinated chickens died within days of exposure.
The hybrid vaccine would probably cost a fraction of a cent per dose,
says virologist Peter Palese of Mount Sinai School of Medicine in New
York City, who coauthored the U.S. study.
The studies complement work, reported in the February Journal of
Virology, that showed similar protection against H5N1 by an injected
vaccine engineered from an adenovirus.
"The Newcastle-hybrid vaccine seems to be cost-effective," says Andrea
Gambotto of the University of Pittsburgh School of Medicine, a coauthor
of the Journal of Virology study. Such a vaccine could be applied much
the same way that large poultry operations spray flocks with Newcastle
vaccine.
These vaccine studies in chickens are proceeding on a track parallel to
efforts aimed at creating a bird-flu vaccine for people. So far, the
virus has infected and killed only people who'd had direct contact with
an infected animal (SN: 9/10/05, p. 171:
http://www.sciencenews.org/articles/20050910/bob10.asp).
Gambotto cautions that while the idea of stockpiling a bird-flu vaccine
for human use has gained acceptance, the notion of using influenza
vaccines in animals remains controversial. Previously developed
vaccines trigger antibodies that are indistinguishable from those
caused by an infection.
However, by generating a distinctive immune response, the new vaccines
might "allow us to differentiate infected birds [from vaccinated birds]
in the population," says veterinarian David Swayne of the U.S.
Department of Agriculture in Athens, Ga., who coauthored the U.S.
study.
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