Welcome to Avian Flu Watch: Global H5N1 Tracker. This week, we're focusing on the current state of the H5N1 avian influenza virus—a pathogen affecting birds, mammals, and, increasingly, humans worldwide—with a close analysis of its geographic spread, key data points, and emerging risks.

Let's start with the numbers. According to the Pan American Health Organization, as of mid-October 2025, the Americas have seen over 5,000 documented outbreaks in birds, with 76 confirmed human infections and two deaths since 2022. Globally, the World Health Organization counts 990 human cases and 475 deaths in 25 countries since 2003, yielding a case fatality rate near 48 percent. Much of the recent surge comes from enhanced detection in mammals, not just birds—making the situation particularly complex.

Now, where are the world's hotspots today? In the Americas, significant outbreaks persist in the US, Mexico, Chile, Uruguay, and Argentina. The US has grappled with over 173 million infected poultry and documented outbreaks in over 1,000 dairy cow herds by late May. Human cases were confirmed in Louisiana, Ohio, Wyoming, and a fatal case in Canada. Mexico and Argentina both reported their first human deaths from H5N1 this year.

In Europe, Germany saw more than 2,000 cranes die, with over 100 farm outbreaks leading to the culling of half a million birds. The UK detected infections in poultry workers—and notably, even a sheep, marking further cross-species transmission. Southeast Asia remains a key region; Cambodia has reported multiple human fatalities in 2025 alone, and Vietnam, China, and the Philippines continue to see outbreaks among both animals and humans.

Describing the global trend, imagine a line graph surging steeply from late 2022, peaking through 2024 as new mammal infections and larger farm outbreaks push numbers higher. By 2025, the curve remains elevated, punctuated by regional spikes—like the wave in North American dairy cattle and marine mammals along South America’s coastline, which saw devastating die-offs in sea lions and elephant seals.

Comparing regions, the US and Latin America now account for a majority of recent infections in mammals and birds, while Southeast Asia continues to report the most human cases relative to population. Europe’s outbreaks—while fewer in number—emphasize high-impact events, such as mass deaths among wildlife and intensive farm culling.

Transmission analysis draws attention to cross-border risks. Migratory bird patterns link outbreaks from eastern Asia to Alaska and down through the Americas, as mapped by studies from geospatial health researchers. Interstate movements of livestock—especially dairy cattle in the US—have enabled rapid viral spread, with mathematical modeling highlighting Arizona and Wisconsin as states at greatest future risk.

Containment efforts have met mixed success. Positive examples include targeted poultry export bans in the Philippines and enhanced testing of cattle exports in the US, limiting spread to new states. However, delays in intervention—such as slow federal orders or incomplete wildlife surveillance—have allowed the virus to jump species and borders unpredictably. Notably, current interventions prevented only a fraction of expected outbreaks, signaling the need for urgent and wider biosecurity improvements.

Emerging variants are a central concern. Genetic reassortment in Southeast Asia has produced new lineages combining genes from globally circulating strains with older local lineages. These hybrids have already caused several human infections in Cambodia and Vietnam, raising fears about pathogenicity and transmission potential.

Finally, travel advisories: Avoid direct contact with wild birds, sick or dead animals, and uncooked poultry in high-risk regions. People visiting affected rural areas—particularly in Southeast Asia, the Americas, and Western...