This year in In the United States, 14 people have tested positive for avian influenza, or bird flu. Nine of them were infected after coming into contact with poultry and four contracted the virus from exposure to dairy cows. The source of the remaining case, the most recent, remains a mystery.
The Centers for Disease Control and Prevention Confirmed the case on September 6Initially detected by the Missouri Department of Health and Senior Services, it is the first known case of bird flu in humans in the country without exposure to a sick or infected animal. On Thursday, health officials said they had not determined how the person acquired the virus.
“At this point, the evidence points to this being an isolated case,” said Nirav Shah, principal deputy director of the CDC, during a press conference.
The case is concerning, however, as it raises the possibility of an alternative source of transmission, either from a person or an unknown source. Health officials say there is no evidence of person-to-person spread at this time. The CDC says its surveillance system has not detected any unusual flu activity in the country and the risk to the general public remains low.
“Our influenza surveillance system is designed to find needles in haystacks,” Shah said at the briefing. “In this case, we found a needle, but we don’t know how it got there.”
The Missouri case is the first to be detected through the country’s national flu surveillance system, rather than through targeted testing of animals. This year, the H5N1 flu virus has been responsible for the decimation of poultry nationwide and the infection of 200 dairy herds in 14 states—the latest in California. It is becoming more and more spreading to other mammalsincluding foxes, mice, raccoons and domestic cats. With more animals harbouring the virus, there is a greater potential for human infection.
It’s not known if that happened in the Missouri case, but it’s one of the avenues health officials say they’re investigating.
“Regardless of the source, it’s concerning because it suggests there’s a lot of virus circulating,” says David Boyd, a virologist at UC Santa Cruz who studies influenza. “This indicates there’s widespread transmission from animal sources.”
On August 22, an adult patient was hospitalized in Missouri for reasons related to underlying medical conditions and also tested positive for influenza. The patient’s specimen was sent to the Missouri State Public Health Laboratory, which determined it did not match currently circulating seasonal influenza viruses.
That prompted the CDC to conduct more testing, which last week confirmed it was a type of bird flu, or H5. The agency was conducting additional testing to determine the subtype of the virus — the “N” part of H5N1. On Thursday, health officials said the patient had a very low concentration of viral genetic material, and because of this, they have not been able to generate a complete genome, including the N part of the virus. However, their data shows the sample is closely related to the H5 virus circulating in dairy cows.
