CDC says bird flu viruses ‘represent pandemic potential’, cites major knowledge gaps

Avian flu still appears to pose a “low risk to the general public” for now, the Centers for Disease Control and Prevention says. But agency scientists ran into roadblocks investigating a human case of the “pandemic potential” virus this year, they said in a new report.

The agency’s epidemiologists were ultimately unable to access a Texas dairy farm where a human was infected with the virus in March, they revealed in attachments to the report published Friday by the New England Journal of Medicine. That prevented investigators from investigating how workers might have been exposed to the virus on the farm.

That’s because the dairy worker who went to a local Texas office to get tested “did not disclose the name of his workplace,” said Lara Anton, spokeswoman for the Texas Department of State Health Services.

They were also unable to collect follow-up samples from the dairy farm worker or their contacts, which could have revealed missed cases, as well as tracking the virus and antibodies against it in the body after an infection.

The worker was not wearing protective glasses or a mask that could have protected him from the virus, according to the report. The virus was probably transmitted through their contaminated hands or virus droplets from sick cows.

It is likely that H5N1 was spreading through dairy farms through the high concentrations of the virus found in the raw milk of infected cows, officials said previously.

The virus had been circulating in cows for about four months before it was confirmed by laboratories on March 25, according to a draft report by U.S. Department of Agriculture scientists released Thursday.

A mutation of the virus in wild birds, a specific “clade” of the virus that scientists call 2.3.4.4b, appears to have allowed bird flu to jump to cows. Several flocks likely became infected during that initial spread before the birds migrated north, officials said.

Since then, at least nine states have detected infections in cows with the virus. Cows largely recover from H5N1, unlike the mass die-offs seen in other species. Some herds with infected cows also remain asymptomatic and continue to produce milk.

Experiments conducted by the Food and Drug Administration show that pasteurized milk remains safe to drink, despite traces of the virus found in grocery store samples. The outbreak has also prompted a new warning not to drink raw milk, which has been linked to the deaths of other animals. like cats.

The current outbreak also stands in stark contrast to how the virus has spread in other virus-infected mammals, typically resulting in what USDA scientists called “dead-end hosts.”

Since then, a handful of variants with potentially concerning mutations have also been detected in cows, the USDA analysis found. If those variants become dominant, they could change the disease caused by H5N1 or make it more likely to spread to other animals or humans.

The cow virus has also been observed spreading from dairy farms to nearby wild birds and poultry, probably carried by milk droplets and contaminated surfaces.

Questions also remain about the exact origins of the virus that infected the Texas dairy worker. While the H5N1 sequence from the human case is closely related to those found in dairy herds, the agency’s analysis found that it also differs in some key ways.

These genetic differences suggest that humans were infected by “an early, slightly different virus” that was circulating in cows before the current cases, or that multiple infections may actually have occurred.

While sequences collected from sick cows on the worker’s dairy farm could have helped CDC scientists answer those questions, the samples were “not available for analysis.”

The human worker has since recovered from his bird flu infection. They only developed conjunctivitis or conjunctivitis, without fever or other common flu symptoms. The worker and his contacts received oseltamivir, an antiviral treatment for bird flu that could also prevent infections.

“While acute conjunctivitis is a clinically mild disease, HPAI A(H5N1) viruses, including those belonging to clade 2.3.4.4b, have pandemic potential and have caused severe respiratory illness in infected humans worldwide,” it says. the report, which was co-authored by CDC scientists. saying.

Missed infections?

Reports from a local veterinarian that other workers in Texas The dairy farms had symptoms of flu or conjunctivitis, Antón said on April 30.

But at least some of those workers with symptoms were tested and found negative for H5N1, health officials in Texas and neighboring New Mexico told CBS News.

“It is likely that there were other people with symptoms who did not want to be tested, so we cannot say with absolute certainty that no one else contracted H5N1. We can say with certainty that there were people sick with other respiratory viruses working on dairy farms.” . Anton said in a statement.

As health authorities and experts rely on dairy workers and their contacts who volunteer to monitor their symptoms and get tested, those tracking the virus have turned to other data sources to look for signs of undetected spread.

A draft study of wastewater samples in a northwest Texas city found that signs of H5N1 had increased in sewers, but also that emergency room trends in the area were decreasing at the same time. They hypothesized that the culprit is the dumping of waste from dairy farms with sick cows, not sick humans.

The CDC has also pointed to emergency room data to ease concerns about undetected H5N1 cases.

“We continue to monitor influenza surveillance data, especially in areas where H5N1 viruses have been detected in dairy cattle or other animals, to detect unusual trends in influenza-like illnesses, influenza or conjunctivitis. “The CDC at this time is not showing any indicators of unusual flu activity in people,” Dr. Demetre Daskalakis, director of the CDC’s National Center for Immunization and Respiratory Diseases, told reporters Wednesday.