Scientists may have cracked the mystery of the origin of the H7N9 avian influenza, which has caused more than 375 infections and 100 deaths. A new study has found that quail and chickens are the likely sources of transmission of H7N9 influenza virus to humans.
First reported in humans in March 2013 in China, this particular strain of avian influenza had not previously been seen in either animals or people. The virus poses an increasing public health concern because of the severity of infection.
As of January, the case fatality rate of all confirmed cases is 22%, according to the World Health Organization. Most known human infections have resulted from direct or indirect contact with poultry. So far, only one case has been reported outside of China, and it's believed that she contracted the virus in China. While previous pandemic threats have tended to fizzle out, scientists believe H7N9 is so deadly because humans lack an existing immunity against the H7 subtype influenza viruses.
"Knowing the likely poultry species lets us target our interventions better to prevent human infections," says corresponding author David Suarez of the U.S. Department of Agriculture.
Early on in the outbreak, sequences from several isolates of H7N9 were made available in public databases. That was when Suarez and his team speculated that most of the genes of H7N9 had come from a poultry virus that had existed in China for many years, and two genes probably came from a wild bird isolate.
Suarez and his colleagues tested their theory by infecting 7 species of poultry with a human isolate of the Chinese H7N9 virus. The virus replicated well in quail and chickens and then quickly infected their cagemates. In other poultry species, the virus did not replicate as well or transmit efficiently. In additional experiments, quail transmitted the virus efficiently, while pekin ducks and pigeons did not. Still, none of the poultry species became noticeably sick when infected with H7N9, a feature of the virus that makes it difficult to detect in birds.
The findings are published ahead of print in the Journal of Virology.
- get the press release
- read the study