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: When Flu Flies the Coop).
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.