H5N1 Shows Increased Adaptation and Transmission Among Mammals; Does It Sound an Alarm for a Potential Pandemic?

The flu virus that is currently causing an outbreak in dairy cows in the US continues to adapt and change. Experts worry that this can lead to possible human-to-human transmission.

A New Viral Outbreak

In a preprint study, scientists from the National Institute of Agricultural Technology (INTA) in Argentina and the University of California, Davis, discovered that the bird flu virus has begun to spread among marine mammals, such as elephant seals. They also found strains of the virus, which can spread to mammals and infect birds.

The findings of the study are discussed in the paper "Massive outbreak of Influenza A H5N1 in elephant seals at Península Valdés, Argentina: increased evidence for mammal-to-mammal transmission." According to the authors, the influence of H5N1 viruses has become more evolutionary flexible and adapting to mammalian species in new ways, which can have global consequences for humans, wildlife, and livestock.

The outbreak of H5N1 started in October 2023 at the Península Valdés in Argentina when experts observed a significant increase in deaths of elephant seals. About 17,000 seal pups were killed by the virus, marking the first known transnational transmission of highly pathogenic avian influenza (HPAI) among mammals.

Led by veterinarian Dr. Marcela Uhart from UC Davis Karen C. Drayer Wildlife Health Center, the research team used genomic analysis to reveal the tendency of H5N1 to separate into distinct avian and marine mammal clades. Identical mutations were found in the viruses from both marine mammals and birds, an indication of their adaptation, especially for mammalian transmission.

According to Dr. Uhart, their research finding is evidence that we should be alert, especially for marine mammals. The more the bird flu adapts to mammals the higher is the chance that it can affect humans.

Virulence of H5N1

H5N1 is one of the strains of the virus that causes highly infectious respiratory disease in birds. It predominantly affects birds. It was first identified in 1996 and has a mortality rate that exceeds 50%.

In 2020, H5N1 made its first global headlines when it caused significant mortality among seabirds in Europe before reaching South Africa. After two years, the virus reached the American continent, with reported cases in Canada, the US, and South America.

The pathogen was first detected in poultry in early 2023. However, it was not until August that symptoms were also shown in marine mammals.

According to virologist Agustina Rimondi, influenza viruses can adapt to new hosts because of their ability to mutate and exchange gene segments. This gives them the capability to adapt to mammalian species.

Scavenging by seagulls and frequent interaction between sea lions likely triggered the spread of the virus. Combined with the high density of the affected colonies, this can create a perfect condition for the virus to spread quickly.

The researchers stressed the importance of understanding the potential effect of this virus on human health and wildlife. They are concerned with the ability of H5N1 to adapt to marine mammals and retain its ability to infect birds because it indicates a high level of evolutionary flexibility. The more the bird flu virus spreads among mammalian species, the greater the risk of acquiring mutations which can enable human transmission.