Noah McCrory
Bird flu continues to appear to pose a “low risk to the general public” for now, according to the Centers for Disease Control and Prevention it says. But agency scientists encountered obstacles in investigating a human case of this virus with “pandemic potential” this year, they said in a new report.
The agency’s epidemiologists were 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. This prevented investigators from looking into how workers could have been exposed to the virus on the farm.
That’s because the dairy worker who went to a local Texas office for testing “did not disclose the name of his place of employment,” 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 track the virus and antibodies against it in the body after an infection.
The worker was not wearing protective glasses or a face mask that could protect him from the virus, the report said. The virus was likely transmitted through contaminated hands or droplets of the virus from sick cows.
H5N1 was likely spreading across dairy farms through the high concentrations of the virus found in 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 report. draft report of scientists from the U.S. Department of Agriculture released on 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 spread to cows. Several flocks likely became infected during the initial spread, before the birds migrated north, officials said.
Since then, at least nine states have detected infections in cows caused by the virus. Cows largely recover from H5N1, unlike the mass deaths seen in other species. Some herds with infected cows have also remained asymptomatic and continue to produce milk.
Experiments carried out by the Food and Drug Administration show that Pasteurized milk remains safe to drink despite traces of the virus found in supermarket samples. The outbreak has also prompted a renewed warning not to drink raw milk, which has been linked to the deaths of other animals. like cats.
The ongoing outbreak also stands in stark contrast to how the virus has spread in other virus-infected mammals, which has often resulted in what USDA scientists have 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 these variants become dominant, it could alter the disease caused by H5N1 or increase the likelihood of it spreading to other animals or humans.
The cow virus has also been detected spreading from dairy farms to nearby wild birds and poultry, likely carried by contaminated milk droplets and surfaces.
Questions also remain about the exact origins of the virus that infected the Texas dairy worker. Although 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 important ways.
These genetic differences suggest that the human was infected by “an early and slightly different virus” that was circulating in cows before the current cases, or that multiple repercussions may actually have occurred.
While sequences collected from sick cows on the worker’s dairy farm could have helped CDC scientists answer these questions, the samples were “not available for analysis.”
The human worker has since recovered from the bird flu infection. They only developed conjunctivitis, or pink eye, without fever or other common flu symptoms. The worker and his contacts received oseltamivir, an antiviral treatment for bird flu that can also prevent infections.
“Although acute conjunctivitis is a clinically mild disease, HPAI A (H5N1) viruses, including those belonging to the 2.3.4.4b clade, have pandemic potential and have caused severe respiratory illness in infected humans worldwide,” says the report. co-authored by CDC scientists. he said.
Missed infections?
Reports from a local veterinarian than other workers in Texas dairy farms showed symptoms of flu or conjunctivitis is true, Anton said on April 30.
But at least some of those workers with symptoms were tested and tested 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,” he said. Anton said in a statement.
With health authorities and experts dependent on dairy workers and their contacts volunteering to monitor their symptoms and test, those tracking the virus have turned to other data sources for signs of undetected spread.
One study project of wastewater samples in a northwest Texas city found that signs of H5N1 had emerged in sewers, but also that emergency services trends in the area were declining at the same time. They hypothesized that dumping waste from dairy farms with sick cows, not sick humans, is to blame.
The CDC also pointed to Emergency Room data to reassure concerns about undetected cases of H5N1.
“We continue to monitor influenza surveillance data, especially in areas where the H5N1 virus has been detected in dairy cattle or other animals, for any unusual trends in influenza-like illness, influenza, or conjunctivitis. CDC’s influenza surveillance systems at this time do not show 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.
