The spread of the highly pathogenic H5N1 avian influenza virus among animals is unprecedented, having been seen on every continent – except Oceania – and the United Nations calls it a “global zoonotic animal pandemic.” .
H5N1 is known to infect more than 350 species of birds and nearly 60 species of mammals, with migratory waterfowl – including ducks, swans, geese and gulls – being particularly susceptible to various avian flu viruses.
Waterfowl infected with H5N1 are normally asymptomatic carriers, but these birds can infect other species (including mammals) along their migratory routes. This global transfer allows the disease to spread and the genetics and virulence of the virus to continually adapt.
Alarmingly, climate change appears to be impacting the emergence of zoonotic viruses like H5N1. As global climate conditions change, birds’ migratory patterns and routes also change.
Higher temperatures and extreme weather have led to large-scale population shifts in various temperate species. These changes have led to the emergence of diseases in areas – and in genetic configurations – that are completely unique and unprecedented.
The H5N1 virus makes it clear that disease surveillance and control efforts are an essential part of any climate change adaptation and mitigation strategy.
H5N1
The ecology and genetics of H5N1 viruses have evolved considerably since their first detection in China in 1997.
The H5N1 virus has been detected in polar regions and the first confirmed case of a polar bear dying from H5N1 was recorded in Alaska in 2022. Antarctica has seen significant mortality rates among its native populations of elephants and fur seals due to exposure to the virus. .
Non-migratory wild birds are very susceptible to H5N1 infections caused by the wings of their more transient cousins. According to the Global Animal Health Information System, there have been approximately 75,000 bird casualties worldwide.
However, efforts to accurately estimate the total number of wild bird deaths due to H5N1 are hampered by issues with data quality and availability.
Meanwhile, a 2022 report on the state of wild birds in the United States estimates that more than three billion birds have been lost, in part due to climate-related factors.
On land, the H5N1 virus has been detected in dairy cattle, and in 2024, a farm worker in Texas was infected with H5N1. These cases suggest that H5N1 is adapting to infect mammalian hosts.
In March of this year, reports began emerging of unusual deaths of young goats on a farm in Minnesota. This same farm had individuals in its poultry flock test positive for H5N1 and the goats and poultry shared similar spaces and water sources. It was later determined that the H5N1 strains found in poultry and goats were closely related.
In May 2024, the U.S. Department of Agriculture confirmed the detection of H5N1 in alpacas on a farm in Idaho. Similar to previous cases, this farm also had the backyard poultry population test positive for H5N1, with unusually high amounts of virus detected throughout the farm. To date, 12 US states have reported H5N1 outbreaks, affecting 101 dairy herds.
The findings of H5N1 on farms, along with recent analysis of viral dispersal patterns, reiterate the importance of climate change altering bird migratory patterns in the spread of viruses across the globe.
Climate change and H5N1
There is growing evidence that climate change is accelerating the global spread and emergence of new H5N1 variants, and that greater seasonal variation favors the emergence of new H5N1 variants.
In North America, warmer winters and earlier springs caused by global warming may allow some humidity-dependent pathogens to survive and spread more easily. Meanwhile, cooler, wetter conditions can improve the survival of flu viruses in bird droppings and contaminated water.
Simply put, the spread of flu viruses around the world is driven by their ability to survive long enough in one place to be able to transmit elsewhere – and climate change is, in some cases, making that survival more likely.
Recent cases of poultry-to-human and cattle-to-human transmission highlight the threats posed by these viruses and the importance of understanding how climate change affects their spread.
Implications and mitigation
The H5N1 virus poses a significant threat to public health, and recent cases in the United States – coupled with the high mortality rates of the H5N1 virus in humans – highlight the need for vigilant surveillance.
Dealing with viruses is always a challenge, but climate change is upending many conventional understandings as changing waterfowl migration patterns and environmental conditions force us to change strategies. Strengthening health care infrastructure and educating communities about the risks of H5N1 are essential elements of a comprehensive response strategy.
It is crucial to promote sustainable agricultural practices, such as improving biosecurity in poultry and cattle farms, reducing stocking density and improving ventilation systems in barns. Smart and innovative agricultural technology can also help track viral infections in poultry houses.
Conservation efforts are essential to maintaining healthy ecosystems and minimizing the spread of the virus. Restoring natural habitats can mitigate the effects of climate change on wild bird populations, reducing the risk of the spread of H5N1.
Going forward, world leaders will need to be vigilant about the trajectory of H5N1. International collaboration on disease management will be crucial to implementing climate adaptation strategies to protect the health of our planet and its people from viruses like H5N1.
Nitish Boodhoo, Research Associate, Department of Pathobiology, University of Guelph and Shayan Sharif, Professor of Immunology and Associate Dean, Research and Graduate Studies, University of Guelph
This article is republished from The Conversation under a Creative Commons license. Read the original article.