H5N1 Virus Evolves, Raising Alarm Over Mammalian Transmission, Human Health Risks

United States: The H5N1 avian influenza virus, currently wreaking havoc among US dairy cows, is increasingly showing adaptability for mammalian transmission, as emerging research in marine mammals indicates. This alarming trend has experts concerned about the potential for human-to-human spread.

In a preprint study awaiting peer review, scientists from the University of California, Davis, and Argentina’s National Institute of Agricultural Technology (INTA) uncovered instances of the virus spreading among elephant seals and other marine species. Additionally, they identified virus strains capable of cross-species transmission between mammals and avians, as per reports by Live Science.

“The notion that H5N1 viruses are evolving with greater flexibility to infect mammals portends significant global ramifications for wildlife, humans, and livestock,” the researchers articulated in their study, recently uploaded to the bioRxiv preprint database on June 1.

The current strain of H5N1 started to spill over human populations in February 2020 and spread among the avian population in Europe before it crossed over to South Africa. In 2022, the virus appeared in North America, and by the beginning of 2023, it reached South America. Alarmingly, in August 2023, it emerged not in birds but in South American sea lions in the Tierra del Fuego archipelago, on the border with Chile.

In October 2023, UC Davis and INTA researchers vividly watched the virus kill off a colony of elephant seals at Punta Delgada at Península Valdés in Argentina. The virus led to the death of more than 17,000 seals, with the percentage of the affected pups estimated at 96% of the total seals born that year.

Genomic analysis revealed the virus from the clade 2.3.4.4b, genotype B3.2 lineage. This lineage, introduced by migratory birds, infiltrated mammalian populations in South America several times between late 2022 and 2023. One particular spillover incident led to a new lineage capable of mammal-to-mammal transmission. The genetic evidence linked outbreaks in Argentina, Chile, Peru, and Brazil, marking the first documented multinational virus spread among mammals, as mentioned by Live Science.

“This is further evidence that vigilance is crucial, particularly for marine mammals,” emphasized Dr. Marcela Uhart, co-lead author and veterinarian at UC Davis Karen C. Drayer Wildlife Health Center’s Latin America Program. “The virus’s increased adaptability to mammals heightens its significance for human health.”

Although the virus can infect humans, such cases are exceedingly rare. The Centers for Disease Control and Prevention has documented four human cases in the US: one in 2022 linked to poultry exposure and three in 2024 related to dairy cattle.

“The virus’s ability to adapt to mammalian hosts is evident from the recurring mutations observed in the mammalian clade,” noted study co-leader Agustina Rimondi, a virologist at INTA, Live Science reported.

Both Uhart and Rimondi stress the importance of ongoing surveillance of the virus in wildlife to comprehend its potential human health implications.

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