H5N1 Bird Flu Adapts to Spread in Mammals, Raising Concern for Humans

Research findings suggest that the H5N1 bird flu virus, responsible for the current U.S. outbreak in dairy cows, is increasingly adapting to spread in mammals. The virus has been detected in elephant seals and other marine mammals in South America, raising concerns among experts that it could potentially evolve to transmit from mammal to mammal and pose a threat to humans.

A preprint study conducted by researchers from the University of California, Davis and the National Institute of Agricultural Technology (INTA) in Argentina provides evidence of the virus spreading among elephant seals. The study also identified versions of the virus that could both spread between mammals and infect birds.

The researchers emphasized that the virus’s ability to adapt and spread in mammals could have significant consequences for wildlife, humans, and livestock. The H5N1 virus, which first began to spread widely among birds in 2020, has now reached South America and has been detected in sea lions and elephant seals.

In August 2023, the virus was found on the Tierra del Fuego archipelago, not in birds but in sea lions. Subsequently, in October 2023, researchers discovered the flu in Punta Delgada on the coast of Península Valdés in Argentina. The outbreak killed over 17,000 elephant seals, including 96% of pups born that season.

Genetic sequencing of the deadly virus revealed a specific lineage called clade, genotype B3.2. The researchers found that this lineage spread from migratory birds into mammals in South America multiple times in late 2022 and 2023. One of these spillovers evolved into a new lineage capable of spreading easily from mammal to mammal.

The genetic data linked mammal outbreaks in Argentina, Chile, Peru, and Brazil, marking the first known multinational mammal-to-mammal spread of the virus. Researchers highlighted the importance of heightened vigilance, particularly for marine mammals, as the virus continues to adapt to mammals.

While the virus can infect humans, reported cases are rare. The Centers for Disease Control and Prevention has identified four cases in humans in the U.S., with only one having occurred in 2022. However, scientists emphasize that continued monitoring of the virus in wildlife is crucial for understanding its potential consequences for human health.

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