Researchers have developed vaccines for two recently emerged strains of avian influenza, H5N1 and H7N9. Since both of these can be passed on to humans, the new vaccines would not only reduce the number and intensity of massive outbreaks within poultry farms, it would also curb human transmission. The work was described in the Journal of Virology last month.
In humans, avian influenza can cause severe respiratory illness, multi-organ disease, and death. The highly pathogenic H5N1 virus was first detected in geese in China back in 1996 and then in humans a year later. Since its reemergence in 2003, human infections have been reported throughout Asia, North Africa and parts of Europe and the Middle East. Human infections with the H7N9 virus were first reported in 2013 in China, and in 2014, a traveler in Malaysia became the first case detected outside of China. So far, hundreds of people have died, and millions of chickens and turkeys have been culled.
"In Southeast Asia there are a lot of markets that sell live birds that people can buy and prepare at home," Kansas State University’s Jürgen Richt explains. "In contrast to the H5N1 virus that kills the majority of chickens in three to five days, chickens infected with the H7N9 virus do not show clinical signs of sickness. That means you could buy a bird that looks perfectly healthy but could be infected. If an infected bird is prepared for consumption, there is a high chance you could get sick, and about one in three infected people die."
To develop a vaccine for bird flu, Richt and colleagues combined two viruses. First, they cloned a vaccine strain of the Newcastle disease virus, which naturally infects bird flocks of all species. They then transplanted a small section of the H5N1 virus into the Newcastle disease virus vaccine – creating a recombinant virus that vaccinated chickens against both the Newcastle disease virus and H5N1. Next, using that same method, the team inserted a small section of the H7N9 virus into the Newcastle disease virus vaccine. When given this recombinant vaccine, the chickens became protected against the Newcastle disease virus and H7N9. The vaccines induced antibodies that protected chickens during subsequent exposure to H7N9 and H5N1 viruses.
"We believe this Newcastle disease virus concept works very well for poultry because you kill two birds with one stone, metaphorically speaking," Richt says in a news release. "You use only one vector to vaccinate and protect against a selected virus strain of avian influenza."
The first H5N1 vaccine was licensed by the US Food and Drug Administration back in 2007 to counter the spread of a pandemic; there’s no H7N9 vaccine for humans, and this is the first study to look at an H7N9 vaccine in chickens. The team says that this method of developing vaccines can also be applied to rapidly emerging strains in the future, including those affecting pigs and other livestock.
[Via Kansas State]