Scientists Raise Concerns Over HPAI H5N1 Virus in Texas Farm Worker

Discovery of huTX37-H5N1 Virus

Scientists from the National Institutes of Health (NIH) are expressing serious public health concerns following the identification of a highly pathogenic avian influenza (HPAI) H5N1 virus in a farm worker in Texas earlier this year. The virus, referred to as huTX37-H5N1, was isolated from the worker’s eye and is believed to have originated from contact with infected dairy cows. Although the worker displayed only mild conjunctivitis, laboratory tests indicated that the virus was lethal in mice and ferrets.

Implications for Raw Milk Consumption

This finding has prompted questions regarding the potential for bird flu transmission through cow’s milk, particularly in light of the increasing popularity of raw, unpasteurized milk. Advocates of raw milk often highlight its health benefits; however, it can also contain harmful pathogens such as the H5N1 virus, posing significant health risks to consumers. The detection of bird flu on dairy farms emphasizes the critical role of pasteurization in ensuring milk safety and safeguarding public health.

Research Findings on Airborne Transmission

Study Published in Nature

In an October 2024 article published in the journal Nature, researchers detailed how the newly identified strain of bird flu transmits more easily through the air than other strains. Scientists from the University of Wisconsin-Madison conducted experiments involving laboratory animals, finding that 17-33% of healthy ferrets, placed near infected ferrets, became infected themselves and exhibited severe illness, mirroring the outcomes of directly infected ferrets.

Genomic Analysis of huTX37-H5N1

Upon analyzing the genome of the conjunctivitis-causing strain, researchers discovered a mutation that enhances its replication efficiency in mammals, thereby increasing its threat to human health.

Concerns about Bird Flu in Cow’s Milk

Precedents of HPAI Strains on Dairy Farms

The discovery of the huTX37-H5N1 virus is not an isolated incident. Earlier in 2024, there was a significant outbreak of highly pathogenic bird flu among U.S. cattle, which spread across herds and infected other animals, including poultry and cats. Epidemiologists have raised alarms about the potential for human infections. Historically, HPAI H5N1 viruses primarily infect birds and have rarely transmitted easily among mammals, but recent events on dairy farms suggest a troubling exception.

Research on H5N1 in Dairy Products

Given the prevalence of dairy products in North American diets, public health researchers are investigating the possibility of bird flu transmission through cow’s milk. In July 2024, Wisconsin researchers found that HPAI H5N1-infected cows had viral particles in their milk, and when ferrets were fed this milk, they became ill. Furthermore, infected ferrets and mice accumulated the HPAI H5N1 virus in their mammary glands, where milk is produced.

Transmission Dynamics and Human Health Risks

Contrasting Transmission Rates

While the virus was effectively transmitted via milk, its spread between ferrets in separate cages was not as rapid; only one out of four exposed ferrets showed signs of infection, with no detectable virus in their bodies. Although this may appear reassuring, DNA sequencing indicated that the strain has mutated, enhancing its ability to infect humans.

Binding Affinity to Human Cells

Researchers assessed the virus’s capacity to bind to proteins on human respiratory cells, which flu viruses utilize to infect cells. The HPAI H5N1 virus displayed the ability to bind to receptors in the human upper respiratory tract, raising concerns about its potential to cause serious illness in humans.

Safety Measures and Treatment Options

Role of Pasteurization

All commercially available dairy milk undergoes pasteurization, significantly reducing the risk of infection from standard milk. However, raw milk remains untreated, making it a potential source for virus transmission.

Insights into H5N1 and Treatment Efficacy

Unlike the less transmissible Bovine H5N1 observed in cow herds earlier this year, huTX37-H5N1 shows airborne capabilities and infects human respiratory cells. Laboratory studies indicate that while most reported human cases during the ongoing H5N1 outbreak have manifested mild symptoms, particularly conjunctivitis, prior exposure to seasonal influenza viruses might confer some degree of protection. Furthermore, the research uncovered that huTX37-H5N1 is susceptible to certain antiviral medications, including favipiravir, baloxavir marboxil (Xofluza), and zanamivir.

References

Gu C, Maemura T, Guan L, et al. A human isolate of bovine H5N1 is transmissible and lethal in animal models. Nature. Published online October 28, 2024. doi:10.1038/s41586-024-08254-7
HPAI in livestock: Animal and Plant Health Inspection Service (no date) HPAI in Livestock | Animal and Plant Health Inspection Service. Available at: https://www.aphis.usda.gov/livestock-poultry-disease/avian/avian-influenza/hpai-detections/livestock (Accessed: 07 November 2024).
Eisfeld AJ, Biswas A, Guan L, et al. Pathogenicity and transmissibility of bovine H5N1 influenza virus. Nature. 2024;633(8029):426-432. doi:10.1038/s41586-024-07766-6