Introduction

The once lively barks of the elephant seals echo along the beaches of Península Valdés, Argentina, but this year, the sounds are subdued. Following a devastating outbreak of H5N1 avian influenza a year ago that claimed over 17,000 elephant seals—including nearly all of their pups—scientists report that only about one-third of the usual population has returned this breeding season.

Expert Insights

Dr. Marcela Uhart, director of the Latin America Program at the UC Davis Karen C. Drayer Wildlife Health Center, expressed mixed feelings: "It's beautiful to walk the beaches now and hear elephant seals again; however, we see the grim reality of carcasses strewn about and the absence of harems, which is undeniably troubling."

Study Findings

A recent study, co-led by researchers from UC Davis and the National Institute of Agricultural Technology (INTA) in Argentina, provides startling evidence of mammal-to-mammal transmission of the virus during the 2023 outbreak, marking a significant milestone in our understanding of H5N1. The findings reveal that the virus spread dramatically among marine mammals, facilitating its crossing into five different countries in southern South America.

Genomic Analysis

Genomic analysis from the study shows an unprecedented evolution of H5N1. It diverged into distinct clades for avian and marine mammal species upon its arrival in South America, according to virologist Agustina Rimondi. "This demonstrates the virus's capacity to adapt to marine mammal hosts, noted by specific mutations detected within its clade. Significantly, we also found that viruses originating from marine mammals can revert back to infect birds, underscoring a pressing need for enhanced surveillance and regional cooperation in wildlife health," Rimondi stressed.

Conservationist Concerns

The harsh realities of this outbreak have shocked conservationists. Valeria Falabella, director of WCS Argentina's coastal and marine conservation division, lamented the devastating effects of avian influenza on the elephant seal population. "The death toll is staggering—more than half of the reproductive population may have perished due to the virus. It will take decades for these numbers to recover to their 2022 levels," she said.

Current Monitoring Efforts

Monitoring efforts are underway to document the health of the recovering elephant seals. While no seals have tested positive for H5N1 in the current breeding season, lingering uncertainties remain. Scientists are still investigating how the virus was transmitted—whether through aerosol, saliva, or feces—and whether surviving seals have developed any immunity.

Global Context

Globally, H5N1 has continued to spread, recently detected among wild birds, poultry, and even livestock. The U.S. Department of Agriculture confirmed its first occurrence in swine just last month, reflecting the virus's evolving threat.

Traveling Path of H5N1

The path of the H5N1 variant clade 2.3.4.4b has been concerning since it began wreaking havoc on seabird populations in Europe in 2020, then making its way to North America and ultimately reaching South America by late 2022. By February 2023, avian influenza hit poultry in Argentina, but it wasn't until August that it was found affecting marine mammals.

Recent Survey Results

A survey conducted in October identified significant mass mortality among a breeding colony of elephant seals in Punta Delgada, with the presence of HPAI H5N1 confirmed in the dead seals and associated seabirds.

Urgent Need for Action

The need for continued monitoring and research is urgent as the virus's adaptability poses potential risks not only to wildlife and ecosystems but to human health globally. Scientists urge the international community to prioritize efforts in studying this evolving virus to mitigate future outbreaks and safeguard both human and animal populations.