The Centers for Disease Control and Prevention states that bird flu, currently, presents a “low risk to the general public.” However, in a recent report, the agency’s scientists encountered difficulties when investigating a human case of this potentially pandemic virus earlier this year.
Epidemiologists from the agency were unable to access a Texas dairy farm where a human contracted the virus in March. This hindered their ability to investigate how workers might have been exposed to the virus on the farm.
According to Lara Anton, a spokesperson for the Texas Department of State Health Services, the dairy worker who sought testing did not disclose the name of their workplace.
Additionally, follow-up samples from the dairy farm worker or their contacts, which could have provided insights into missed cases and tracked the virus and antibodies, were not collected.
The report indicated that the infected worker did not use protective eye goggles or a face mask, leaving them vulnerable to the virus, likely transmitted through contaminated hands or droplets from sick cows.
Authorities had previously suggested that H5N1 was spreading through dairy farms via the high concentrations of the virus found in the raw milk of infected cows.
The virus had likely been circulating in cows for about four months before its confirmation by labs on March 25, according to a draft report from U.S. Department of Agriculture scientists.
A mutation in wild birds, specifically a clade known as 2.3.4.4b, seemingly facilitated the transmission of bird flu to cows. Multiple herds were likely infected before the birds migrated north.
Subsequently, at least nine states have reported cow infections from the virus, with cows generally recovering unlike other species experiencing mass die-offs.
Experiments by the Food and Drug Administration confirmed the safety of pasteurized milk despite traces of the virus found in samples from grocery stores. The outbreak reiterated warnings against drinking raw milk, which has been linked to deaths in other animals.
This ongoing outbreak differs from previous instances of the virus spreading in mammals, which often resulted in dead-end hosts, according to USDA scientists.
The USDA analysis identified several variants with potentially concerning mutations in cows, which could alter the disease caused by H5N1 or increase the likelihood of spread to other animals or humans.
The virus has spread from dairy farms to nearby wild birds and poultry, likely transported by contaminated milk droplets and surfaces.
Questions persist about the exact origin of the virus that infected the Texas dairy worker. While closely related to strains found in dairy herds, the virus from the human case differs in key aspects, suggesting either an early, slightly different virus or multiple spillover events.
Unfortunately, samples from sick cows on the worker’s farm were unavailable for analysis, which could have aided CDC scientists in answering these questions.
Fortunately, the infected worker has since recovered, experiencing only conjunctivitis without fever or other common flu symptoms. The worker and their contacts received oseltamivir, an antiviral treatment for bird flu, as a preventive measure.
“While acute conjunctivitis is a clinically mild illness, HPAI A(H5N1) viruses, including those belonging to clade 2.3.4.4b, pose pandemic potential and have caused severe respiratory disease in infected humans worldwide,” the report co-authored by CDC scientists said.
