番茄社区

The bird flu outbreak affecting poultry farms across the U.S. isn't a cause for concern just yet, but disease surveillance specialists are doing their best to stop the spread and prevent any human cases, experts said.

During this wave of highly pathogenic avian influenza (HPAI) H5N1, the first outbreak in a commercial flock occurred among turkeys in Indiana in , and since then 18 states have reported infections in commercial flocks, .

HPAI previously had been detected in a wild bird in South Carolina on . Prior to that, HPAI hadn't been detected in the U.S. since 2016, according to the USDA.

"With the arrival of this virus on our doorstep, we need to be on high alert to quickly detect and respond to outbreaks in our poultry flocks," said Jack Shere, DVM, PhD, associate administrator of USDA's Animal and Plant Health Inspection Service, during a .

Discussing the last major outbreak of HPAI in the U.S., in 2015, Shere said, "We do not want to re-live that event. More than 50 million birds died or had to be culled as a result of that virus. Producers lost $1.6 billion and the overall impact to the U.S. economy was thought to have exceeded $3 billion."

Denise Derrer Spears, public information director for the Indiana State Board of Animal Health, told 番茄社区 that the state had to cull about 171,000 birds from six flocks that were affected, but conditions have significantly improved since those early cases in February.

"We're making good progress. We were able to release all six control areas," she said, referring to the six sites with HPAI cases and the surrounding 10-km radius.

"Any time there's a case, there's a sizeable response to stamp it out," she added.

Spears said the 2015 outbreak didn't affect Indiana farms as severely as other parts of the country, but the state did suffer a much more severe outbreak in January 2016. This year's outbreak in her state doesn't seem to be as severe as it is for other locations. South Dakota is being hit particularly hard right now, she noted.

HPAI H5N1 is an influenza type A virus that first emerged in southern China and led to large poultry outbreaks in Hong Kong in 1997, resulting in 18 human infections, . The virus was controlled, but not eradicated, and re-emerged in 2003, spreading widely among birds throughout Asia and then later in Africa, Europe, and the Middle East.

The first time the virus was detected in North America was in 2014, and it caused widespread poultry outbreaks and deaths of wild birds in the U.S. and Canada before it disappeared in 2016, the CDC noted.

Globally, there have been more than 860 human infections since 2003, with a substantial mortality rate of about 53%, according to the CDC.

CDC spokesperson Nick Spinelli told 番茄社区 via email that the outbreak "remains primarily an animal health issue at this time," and confirmed that no cases have been detected among people exposed to infected birds at U.S. poultry farms. The agency also maintained that the "health risk to the general public is low."

"CDC has been comparing properties of current and past H5N1 bird flu viruses, and found that the H5N1 bird flu viruses detected in the U.S. in late 2021 and 2022 are different from the H5N1 bird flu viruses that circulated in much of the world in the past," he said.

"So far, current H5N1 bird flu viruses lack changes seen in the past that have been associated with bird flu viruses spreading easily among poultry, infecting people more easily, and causing severe illness in people," Spinelli added. "However, we are taking routine preparedness measures to be ready in case human infections with these viruses happen, and will continue ongoing assessment of the risk posed by these viruses, including conducting additional laboratory work to further characterize current H5N1 bird flu viruses."

Concerns stem from the fact that any influenza A viruses circulating among poultry have the potential to recombine with human influenza A viruses and increase transmissibility among humans. If these avian viruses evolve to efficiently transmit among humans, the world could face a pandemic with "potentially high rates of illness and death worldwide," .

That's why the scientific community was up in arms a decade ago when two researchers reported that they had modified . Critics worried that any action that could improve the virus's transmission ability could pose a pandemic risk, especially if it accidentally or maliciously found its way out into the world.

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