THE WASHINGTON POST: Rare bird flu strain found in California raises potential of wider spread

A new strain of avian influenza has been identified for the first time in the United States, raising concerns that the virus is transforming in a way that could eventually cause wider outbreaks among humans.

U.S. officials disclosed the discovery of the virulent H5N9 strain at a California duck farm in a report in recent days to the World Organization for Animal Health, which maintains a database of animal disease threats.

That disclosure comes as the United States confronts a growing outbreak of another bird flu strain, H5N1, that is spreading in poultry farms across the nation and has infected dairy cows for the first time. Human cases have been sporadic and confined mostly to dairy workers exposed to sick animals.

The H5N9 strain itself does not pose a grave threat to humans, officials and experts said.

But scientists are worried that the continuing spread of H5N1, alongside seasonal flu and other strains, could produce new versions of the virus that spread more easily among humans. That scenario is caused by “reassortment,” the exchange of genetic material when hosts are infected with multiple versions of a virus.

The U.S. Agriculture Department’s Animal and Plant Health Inspection Service, which is investigating the California outbreak, confirmed that the duck farm case does stem from reassortment of the H5N1 virus circulating in U.S. birds. But the agency said the finding was not unexpected.

Public health experts warn that previous bird flu pandemics have started because of reassortment.

“It does suggest there’s enough virus around that reassortment might become more frequent,” said Angela Rasmussen, a virologist at the Vaccine and Infectious Disease Organization at the University of Saskatchewan in Canada. “With enough H5 in these animals and enough seasonal flu in humans, you get them together, and you have a recipe for a potential pandemic virus.”

Both H5N1 and H5N9 cases were discovered in a Merced County commercial duck meat farm in late November. State officials quarantined the facility, and nearly 120,000 birds were killed. Genetic sequencing in January confirmed the new strain, the first of its kind in the United States, triggering the report.

Steve Lyle, a spokesperson for the California Department of Food and Agriculture, another agency investigating the outbreak, said the agency is taking no additional action because the strain was not unexpected, the flock has been euthanized, and the farm would be cleaned and tested for viable virus before birds return.

The H5N9 strain is not completely unfamiliar. Less virulent versions have been discovered in birds in the United States previously, and highly virulent versions similar to that found in Merced County have been detected in other countries. Highly virulent versions are more likely to kill birds but are not necessarily a greater threat to humans.

Either way, health experts said the discovery underscores the urgency of containing H5N1. Even if there is no surge of humans killed or hospitalized, epidemiologist Jennifer Nuzzo said, an uncontained outbreak can be expensive.

“The fact that these [agricultural] operations are having to cull their flocks is costly. We see that when we look at the cost of eggs in the store,” said Nuzzo, director of the Pandemic Center at Brown University’s School of Public Health. “The fact that cows can continue to get infected is ultimately going to prove costly.”

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