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A strain of the bird flu virus has been detected in a human in Texas

MARY LOUISE KELLY, HOST:

There are some troubling developments in the outbreak of bird flu. A strain of that virus has been spreading in wild birds and chickens. Now it is being detected in dairy cattle in the U.S. And just yesterday, health officials in Texas announced a human case. NPR's Will Stone has our report.

WILL STONE, BYLINE: This is only the second human case detected in the U.S. during this current outbreak. About two years ago, this strain of bird flu started tearing through the country's poultry supply. Around that time, a person working with sick birds in Colorado became infected, but the case was mild. That's true of this latest human infection in Texas. The person's only symptoms were eye redness - this after being in contact with dairy cattle that were likely infected.

LOUISE MONCLA: But any time there's a human case, it's, of course, concerning.

STONE: That's Louise Moncla, a virologist at the University of Pennsylvania.

MONCLA: While it's very unusual to see these viruses in cows - and we don't fully understand what is happening there yet - this human infection, you know, is perhaps not entirely surprising.

STONE: That's because this person was infected by direct exposure to a sick animal, which is the way people tend to be infected by these viruses. It's unclear how many dairy cattle are being affected. Cases were confirmed in Michigan, Texas and Kansas and are suspected in other states. Federal officials say there is no concern right now about the commercial milk supply because products are pasteurized. Joe Armstrong is a veterinarian at the University of Minnesota who has tracked the outbreak in dairy cattle.

JOE ARMSTRONG: The big thing to note is we're not seeing mortalities with this at all.

STONE: It's believed wild birds are the initial source of the infection in cattle, but a central question for scientists is whether cows are now spreading it among each other.

ARMSTRONG: I'd be very surprised if this was not being spread from cow to cow - the way it's acting, the way people are telling me it gets on their farm and moves.

STONE: Richard Webby agrees. He's a virologist at St. Jude Children's Research Hospital and thinks it's likely cows are passing it to each other. He says the initial samples collected from cattle offer some reassurance, though.

RICHARD WEBBY: There's nothing in the sequence of the virus that screams this virus has changed, and that's why these cows are getting infected. It just seems to be fairly typical of the viruses that have been detected in birds in various regions.

STONE: Already, there are many examples of mammals getting infected with bird flu in the last few years, including outbreaks in marine mammals in South America and on a mink farm in Spain. Webby says there's a general concern with mammal-to-mammal transmission.

WEBBY: That gives the virus the most opportunities to adapt to their host - to say, yeah, OK, virus, you need to change from being a bird virus and change to being a mammal virus.

STONE: And obviously, humans come into contact with cows more often than wild birds. But Webby says there's no proof that avian influenza in cows is necessarily more dangerous for humans. The outbreak has raised concerns about pandemic readiness. Dr. Wilbur Chen has worked on developing avian influenza vaccines. He's at the University of Maryland's Center for Vaccine Development and Global Health. He says the U.S. has several vaccines for H5N1 bird flu in its stockpile that were developed for other strains.

WILBUR CHEN: At least we've got something on the shelf that matches an H5, but whether they match closely is up to interpretation.

STONE: He says there are ingredients that can be added to the vaccine to help it cover mismatched strains. And then there is mRNA technology - what was used for COVID - that could be leveraged for new vaccines. Chen says preparation for avian influenza goes back decades, and the government should continue that work.

CHEN: The preparation may include - ah, well, we've got now a human case with this virus. Let's just start manufacturing limited quantities. What's the harm?

STONE: But he and other experts emphasize the risk is still low for the average American. Dr. Ashish Jha is dean of Brown University's School of Public Health.

ASHISH JHA: If you start seeing it widespread in farm workers, then you want to think about vaccinating farm workers. If you start seeing it in non-farm workers with evidence of human-to-human transmission, that's when you start then wanting to think about vaccinating a much broader set of the population.

STONE: But he says the U.S. is not there yet. In general, human-to-human transmission of bird flu is very rare. And so far, there's no indication that has changed.

Will Stone, NPR News. Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Will Stone