A person in Louisiana has been hospitalized with a severe case of highly pathogenic avian influenza (Type A H5N1), according to a Centers for Disease Control and Prevention statement released Wednesday. It’s the first ever confirmed instance of a severe bird flu infection in the United States and the first reported human case of bird flu in Louisiana.
The patient was not infected via work at a poultry or cattle facility, but rather at their own home. They had exposure to sick and dead birds in a backyard poultry flock, according to the health agency. This marks the first confirmed human case of avian influenza linked to a backyard flock in the U.S., per the CDC.
So far, there’ve been 61 known human infections in the current outbreak, but all had been relatively mild until now. The Louisiana case was confirmed by the CDC on Friday, and marks a potential turning point in how health experts view the virus’ spread.
[ Related: Can we prevent a bird flu pandemic in humans? ]
Bird flu has been circulating widely among wild and farmed birds in the U.S. since 2022. Many mammals have also been infected in the outbreak, including dairy cattle, in a widening agricultural and public health crisis that began in March .
Since 1996, H5N1 has been reported in 23 countries and infected about 1,000 people. In previous H5N1 outbreaks around the world, severe infections have been more common and mortality in people has been high, with a case fatality rate of around 50 percent. For months now, scientists and public health experts have openly wondered why the current U.S. bird flu outbreak had only resulted in mild cases among humans, even as it proved deadly to other mammals.
Speculative theories have included that the mode of exposure incurred by dairy workers through milking has led to milder cases, that people are being exposed to less of the virus, that previous outbreak fatality rates have been a significant overestimate as lesser infections go unreported, and that virus had mutated to be less severe in humans. Yet none of these explanations alone is sufficient to fully explain what’s been observed so far, and all have pitfalls, leaving the question of illness severity unresolved according to reporting from STAT News.
It’s difficult to draw any conclusions from an individual infection. However, with a severe H5N1 case confirmed, the chance that all currently circulating forms of the virus are inherently less dangerous than in the past appears smaller. At least one of the bird flu variants present in the U.S. is capable of causing severe disease in people.
Multiple avian flu variants are circulating simultaneously and new ones emerge as the virus mutates. Through genetic sequencing, CDC investigators have determined that the particular viral genotype present in the Louisiana patient is the same as one that’s been detected among wild birds and poultry in the U.S. and Canada, but distinct from the type detected in dairy cows and some poultry outbreaks.
Though sporadic human infections continue to emerge, person-to-person transmission–the biggest risk factor for a bird flu pandemic–has yet to be detected. The CDC maintains that the risk bird flu poses to the general public remains low. However, the newly confirmed severe infection highlights that it’s not just agricultural workers who can become ill.
Anyone with exposure to wild or domestic animals, particularly birds, should take precautions to avoid infection, the agency says. People should avoid contact with sick or dead animals, avoid touching surfaces contaminated by animals suspected to have avian influenza, and those who can’t avoid contact should wear protective equipment.
Every infection avoided reduces the opportunities that A(H5N1) has to mutate and become readily transmissible between people. Though definitively preventing a bird flu pandemic is impossible, health agencies, farms, and individuals can take steps to minimize the possibility.
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