Biologists looking for an efficient way to halt the spread of avian flu have hit upon a promising twofer. By inserting an avian flu gene into a vaccine that protects against another bird malady, researchers have developed a vaccine that could combat both. If successful, the vaccine may offer an alternative to the mass slaughterings that have cost the world's poultry industry millions in lost sales.
Most commercial chicken farms vaccinate animals against the highly contagious Newcastle virus, which can decrease egg production or kill domestic poultry and some wild birds. Research teams in Germany and the United States, working independently, wanted to know if the Newcastle disease vaccine (NDV) could be altered to deliver protection against avian influenza. There currently is no vaccine for avian flu, which is caused by a highly contagious virus that is often fatal to birds and can be passed to humans (ScienceNOW, 9 February).
A group led by molecular biologist Angela Römer-Oberdörfer of the Friedrich-Loeffler Institute in Riems, Germany, added a gene from the bird flu virus to a commercially available Newcastle vaccine. The gene, called H5, is one of 16 subtypes of hemagglutinin, a protein that binds the avian influenza virus to the cells it infects. When the researchers exposed chickens to lethal doses of the avian influenza virus and the Newcastle virus, birds inoculated with the recombinant vaccine produced antibodies against both viruses, offering protection against both diseases.
Microbiologist Peter Palese from Mount Sinai Medical School in New York City led the second team, which added the avian flu H7, another hemagglutinin subtype, to a weakened strain of the Newcastle vaccine. When exposed to an H7 strain of avian influenza, 90% of the vaccinated chickens were protected, and all were immune to the Newcastle virus.
Newcastle vaccine can be administered through a spray or by adding it to the animals' drinking water. The genetically modified vaccine could be delivered the same way, Palese says. What's more, he adds, the vaccine can be altered to carry genes from any of the hemagglutinin subtypes.
The studies, which appear online today in the Proceedings of the National Academy of Sciences, are "scientifically interesting," says Mark Tompkins, who studies influenza vaccine development at the University of Georgia, Athens. But Tompkins warns that repeated vaccinations with distinct hemagglutinins would probably be needed to protect birds from the many strains of avian influenza virus.
"Repeat vaccination with a different subtype would not be possible," Palese admits, because after the first vaccination, the animals will be immune to the Newcastle virus, rendering the vaccine useless. However, he adds, because most chickens are slaughtered and sent to market within three to four months, there’s little need for repeat vaccinations.