The spread of the highly pathogenic avian influenza virus H5N1 among animals is unprecedented, having been detected on all continents except Oceania, and the United Nations has described it as “a global zoonotic animal pandemic”.
H5N1 is known to be capable of infecting more than 350 species of birds and about 60 species of mammals, with migratory waterfowl – including ducks, swans, geese, and gulls – being particularly susceptible to various avian-borne influenza viruses. Waterfowl infected with H5N1 are generally asymptomatic carriers, however, these birds can infect other species (including mammals) along their migratory routes. This global infection allows the disease to spread, and allows virus genetics and virulence to continually adapt.
Worryingly, evidence indicates that climate change is influencing the emergence of zoonotic viruses such as H5N1. As global climate conditions change, bird migration patterns and routes are also changing. Higher temperatures and extreme weather have caused massive population shifts in a range of temperate species. These changes are leading to diseases emerging in regions – and in genetic configurations – that are completely unique and unprecedented.
H5N1 is a clear indication that disease surveillance and response efforts are an essential part of any climate change adaptation and mitigation strategy.
H5N1
There have been significant developments in the ecology and genetics of H5N1 viruses since they were first discovered in China in 1997.
H5N1 viruses have been detected in polar regions and the first confirmed case of a polar bear dying from H5N1 was reported in Alaska in 2022. Antarctica has seen a significant increase in mortality in its native elephant and fur seal populations as a result of exposure to the virus.
Non-migratory wild birds are highly vulnerable to H5N1 infection brought on the wings of their more transient cousins. According to the World Animal Health Information System there have been about 75,000 bird casualties worldwide. However, attempts to accurately estimate the total number of wild birds that have died as a result of H5N1 are hampered by problems in the quality and availability of data.
Meanwhile, a 2022 report on the status of wild birds in the United States estimates that more than three billion birds have disappeared due to climate-related factors.
On land, H5N1 viruses have been found in dairy cattle, and in 2024, a Texas farm worker was found to be infected with H5N1. These cases suggest that H5N1 is adapting to infect mammalian hosts.
In March of this year, reports began to emerge of unusual deaths of young goats on a farm in Minnesota. One individual from a poultry flock on the same farm had tested positive for H5N1, and the goats and poultry shared the same space and water source. It was later determined that the H5N1 symptoms in both the poultry and goats were highly correlated.
In May 2024, the US Department of Agriculture confirmed the detection of H5N1 in alpacas on a farm in Idaho. As in previous cases, this farm also had a backyard poultry population test positive for H5N1, with an unusually high amount of the virus found throughout the farm. To date, 12 US states have reported H5N1 outbreaks, with 101 dairy herds affected.
Read more: A measure of prevention: now is the time to act on H5N1 avian flu, because the risk is too great
The discovery of H5N1 in farms, along with recent analysis of virus spread patterns, reiterate the importance of climate change due to changes in bird migration patterns in the spread of viruses around the world.
Climate Change and H5N1
There is growing evidence that climate change is increasing the spread and emergence of new H5N1 variants globally, as well as evidence that greater seasonal variation is driving the emergence of new H5N1 variants.
In North America, warmer winters and earlier springs caused by global warming may allow some moisture-dependent pathogens to survive and spread more easily. Meanwhile, cool and wet conditions may increase the survival of influenza viruses in bird droppings and contaminated water.
(AP Photo/Richard Vogel)
Put simply, the spread of influenza viruses around the world depends on them surviving long enough in one place to spread 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 threat posed by these viruses and the importance of understanding how climate change is affecting their spread.
Implications and mitigation
H5N1 viruses pose a major threat to public health, and recent cases in the United States – as well as the high mortality rate of H5N1 in humans – underscore the need for vigilant monitoring.
Tackling viruses is always a challenge, however, climate change is upending many conventional wisdoms as waterfowl migration patterns and environmental conditions force us to alter strategies. Strengthening healthcare infrastructure and educating communities about H5N1 risks are essential components of a comprehensive response strategy.
Read more: How climate change affects the spread of disease – four key points
It is important to promote sustainable agricultural practices such as improving biosecurity in poultry and cattle farms, reducing livestock population density, and enhancing barn ventilation systems. Innovative smart farming techniques can also help track viral infections in poultry barns.
Conservation efforts are essential to maintain healthy ecosystems and reduce the spread of the virus. Restoring natural habitats can reduce the effects of climate change on wild bird populations, reducing the risk of H5N1 spreading.
In the future, global leaders will need to remain vigilant regarding 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 inhabitants against viruses such as H5N1.