This is Avian Flu Watch: Global H5N1 Tracker, your weekly data briefing monitoring the worldwide spread of highly pathogenic avian influenza H5N1 as of October 18, 2025.

Globally, H5N1’s profile remains grave. According to the World Health Organization, 986 human cases from 25 countries have been reported since 2003. In 2025 alone, 26 new confirmed human infections with A(H5N1) have occurred, according to CDC summaries. The true burden likely exceeds official tallies due to widespread outbreaks in animals, evolving viral lineages, and uneven surveillance.

Let’s break down current hotspots and case numbers. The United States has emerged as a key epicenter, with CDC and UNMC reporting over 173 million infected poultry, around 1,072 dairy cow herds affected, and three confirmed human cases this year—down from 67 last year. California reports eight times as many cattle outbreaks as any other state, followed by Texas, New Mexico, and Kansas. Modeling from Nature shows the majority of disease burden in West Coast dairy herds, but risk is rising in Arizona and Wisconsin. The U.S. recorded its first human death from H5N1 in Louisiana in January, and the virus is spreading within mammalian populations, including cattle for the first time.

South America continues to suffer extensive wildlife impacts. Argentina, Uruguay, Peru, and Chile together have lost at least 600,000 wild birds and 50,000 mammals since 2022. Upwards of 24,000 sea lions and 70% of southern elephant seal pups died in the 2023 breeding season in surveyed areas, with some Península Valdés sites in Argentina reaching 96% seal mortality.

In Asia, Cambodia reported three H5N1 deaths this year, linked to consumption and contact with sick poultry. India and Mexico each confirmed fatal human cases in April. China has reported over 275 cases among wild birds in Qinghai, with evolutionary analysis indicating close genetic ties to South Korea and Japan strains, likely driven by migratory birds along major flyways.

On visualization trend lines, the global epidemic curve for H5N1 in humans remains jagged but persistent, as shown by Our World in Data and WHO. Initial outbreaks peaked in 2022–2023, slowed in early 2024, but agricultural cases remain high, fueling cross-species risk. Comparative statistics indicate animal outbreaks in five geographic regions this quarter, with 304 new outbreak events according to FAO’s situation update.

Cross-border transmission patterns underscore the importance of migratory flyways and livestock trade. A geospatial study in AGU Publications highlights how wild bird migrations connect the Arctic, East Asia, Europe, and South America, shifting H5N1 into new territories. In the U.S, interstate movements of dairy cattle have facilitated the spread despite federal orders requiring testing; urgent, farm-focused biosecurity is needed.

Among notable containment efforts, bans on poultry exports from high-risk countries like Japan, Belgium, and France, and mass culling of over 20 million U.S. chickens in late 2024, helped curb immediate spillover. However, modeling shows that current interventions prevent only a fraction of outbreaks, with limited impact on broader transmission. Cambodia’s rapid genetic sequencing collaboration with WHO and CDC isolated old and new clades to inform containment, averting widespread human transmission.

Emerging variants of concern include the D1.1 mutation, discovered in Nevada dairy cattle in February 2025, which suggests independently evolving viral lineages with potentially heightened cross-species transmissibility.

For travel, the CDC and WHO recommend heightened vigilance in all regions with active avian or mammal outbreaks. Avoid contact with wild birds and livestock; travelers to hotspots like Cambodia, southern Brazil, or U.S. West Coast should heed local restrictions and health advisories.

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