New variant of H5N1 bird flu spreads to marine mammals, heightening concerns for human transmission

Amidst the global focus on the COVID-19 pandemic in 2020, a new and concerning viral threat emerged, largely unnoticed. While attention was diverted, the highly pathogenic avian influenza virus, H5N1, quietly evolved into a new variant, labelled 2.3.4.4b, presenting a significant development in its transmission pattern.

A recent study has unveiled a startling revelation: H5N1, traditionally associated with avian populations, has breached into marine mammals. Instances of the virus have been detected in marine animals along the Atlantic coast of South America, prompting concerns over potential transmission to humans.

Researchers conducted an analysis of brain samples from deceased animals in an affected sea lion rookery in Argentina. Alarmingly, all samples, encompassing sea lions, fur seals, and terns, tested positive for H5N1, specifically the 2.3.4.4b variant.

This mutation is notable for its ability to infect both avian and marine species, indicating a concerning adaptability of the virus. Scientists fear the likelihood of a multi-species outbreak as the virus infiltrates diverse food chains within the region.

Previous observations of similar mutations in sea lions from Peru and Chile, as well as a singular human case in Chile, underscore the gravity of this development. Termed a "New onster" by senior author Marcela Uhart, the variant initiated mass die-offs among seabirds in Europe before spreading globally, eventually reaching South America in 2022.

The true extent of the virus's impact became evident in August 2023 when it ravaged sea lion populations at the southern tip of the continent, subsequently spreading northward. Mortality rates among marine mammals, particularly elephant seal pups, soared to alarming levels, reaching 96% in surveyed areas by November 2023.

Since its introduction to South America, H5N1 has claimed the lives of over six lakh wild birds and 50,000 marine mammals. While human transmission remains relatively low-risk, ongoing replication within mammalian hosts poses a concerning escalation of the threat.

As the virus progresses southward, scientists express grave concerns regarding its potential impact on Antarctica's unique wildlife, notably penguins. To address this looming threat, surveillance efforts are underway in Antarctica to monitor the virus's spread and its potential consequences on vulnerable species.

These findings have been published in Emerging Infectious Diseases.