This is Avian Flu Watch: Global H5N1 Tracker, your data-driven update on the worldwide spread of highly pathogenic avian influenza as of October 2025. Let's break down the numbers and explain what the world's latest surveillance is revealing.

Globally, the confirmed H5N1 burden in 2025 is steep: 986 human cases and 474 deaths, with a fatality rate of 48 percent according to the World Health Organization. Southeast Asia remains the epicenter for human cases, notably Cambodia, which accounts for a significant percentage of the total, with 26 reported infections and eight deaths. In the Americas, five countries have reported 76 human infections since 2022, including two fatalities, as summarized by the Pan American Health Organization.

Trends in animal populations are equally worrisome. The US alone has tallied over 174 million affected birds across all states and nearly 1,700 livestock herds testing positive, with Texas, Idaho, Colorado, Michigan, and Ohio hardest hit. Spillover into cattle and mammals has expanded, reflected in recent outbreaks among dairy herds and new genetic variants, such as the D1.1 mutation detected in Nevada dairy cattle this February.

If you’d visualize the epidemic’s trajectory, you’d see a sharp upward curve through 2024 and into 2025, marked by new case surges each quarter in known hotspots—Cambodia, southern China, US West Coast states, and Argentina’s Pacific rim. Side-by-side comparison with the previous five years reveals an unparalleled geographic spread: more countries report outbreaks than at any point in H5N1 history, including new incursions into Antarctica and marine mammal populations.

Cross-border transmission is largely driven by migratory bird flyways and agricultural trade. The East Asian-Australasian migratory network has been pivotal in virus dissemination from China's coastal provinces to Southeast Asia and even toward Oceania. In South America, viral phylogeny shows distinct transmission routes linking Argentina, Chile, Uruguay, and Brazil, underscoring the need for coordinated surveillance across national boundaries.

On containment, several countries have implemented rigorous biosecurity and movement controls, notably China and the European Union, curbing poultry outbreaks and slowing mammalian spillover. The United States has established interstate testing on cattle exports, yet experts warn these measures have not sufficiently reduced risk, with modeling indicating persistent outbreak potential in West Coast and emerging risk for Arizona and Wisconsin. In contrast, Cambodia’s containment is struggling, hampered by limited resources and high poultry density.

Emerging variants are prompting heightened scientific concern. The D1.1 lineage observed in US cattle exhibits signs of mammalian adaptation, while Asian isolates reveal enhanced competence for cross-species transmission. These mutations expand the host range and complicate detection and control strategies.

Finally, travel advisories remain fluid. Health authorities recommend travelers avoid live animal markets, farms, and direct contact with wild birds and livestock in affected regions. Essential travel to Cambodia, southern China, and US outbreak states should include enhanced personal hygiene and adherence to local health advisories. Those working in agriculture should follow strict biosecurity protocols.

That wraps up this week’s Avian Flu Watch: Global H5N1 Tracker. Thanks for tuning in and be sure to return next week for more global updates. This has been a Quiet Please production. For more, check out Quiet Please Dot A I.

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This is Avian Flu Watch: Global H5N1 Tracker—a data-focused update on the worldwide spread of highly pathogenic avian influenza, H5N1.

As of October 2025, H5N1 continues to affect both animal and human populations across continents. According to the World Health Organization, there have been 973 confirmed human cases since 2003, with 470 deaths, representing a case fatality rate of about 48 percent. In the last year alone, new clusters of human infections have emerged in Cambodia, India, Mexico, the United States, and the United Kingdom, with cases frequently linked to direct contact with infected poultry or, more recently, contaminated mammalian hosts.

Let’s break down the current hotspots. Southeast Asia remains a focal point, with Cambodia reporting three fatal human cases since January 2025. India and Mexico each reported fatal human cases this spring, underlining the virus’s increasing geographic reach and ability to cross traditional species barriers. In the United States, the CDC has tallied multiple human cases in 2025, notably in Louisiana, Ohio, and Wyoming, with the country continuing to experience mass poultry culls, including the loss of 20 million chickens in late 2024.

Visualizing recent trend lines, data from PAHO reveals a sharp increase in animal and human infections in the Americas from late 2024 through 2025. Charts show a continued upward trend, especially in the US West Coast states, where mathematical models cite persistent outbreaks among dairy herds, and the risk of spillover to other states like Arizona and Wisconsin remains significant. Across Asia, figures from WHO highlight recurring surges in Cambodia and Viet Nam, while Europe and the UK see a steadier, moderate increase in outbreaks.

Comparative statistics show that, in 2025, outbreaks in mammals—including dairy cattle, seals, and even polar bears—have reached unprecedented levels. These cross-species jumps are concerning; for example, the US first detected H5N1 in dairy cattle in early 2024, with ongoing transmission facilitated by cattle movement between states, despite federal testing and movement restrictions. Genetic sequencing in the Middle East and Greater Mekong region shows evidence of viral reassortment, as older and newer clades recombine, complicating containment.

Patterns of cross-border transmission are notable along migratory bird flyways and through livestock trade. Outbreaks frequently occur near borders where animal trade is common, such as between Egypt and Israel, Turkey and neighboring countries, or across the US-Canada and US-Mexico borders. Wild bird migrations remain a critical factor in transcontinental spread, from the Arctic all the way to South America, including recent incursions into Antarctica’s wildlife.

Notable containment efforts include swift poultry culls and export bans in the UK, Philippines, and Brazil, and increased farm biosecurity measures in the US, yet gaps in surveillance and uneven implementation have hampered broader success. Failures are most evident where delayed detection allowed the virus to establish in new species or regions, as seen with the late 2024 spread into US dairy cattle.

New variants of concern have been reported, including reassorted strains that blend genes from both the 2.3.4.4b and older 2.3.2.1c clades in Southeast Asia, raising alarms over increased zoonotic potential and complicating vaccine development. Surveillance agencies warn that these changes may enable more efficient mammal-to-mammal or even limited human-to-human transmission.

As for travel, health authorities urge caution when visiting outbreak regions, especially for those involved with poultry or livestock farming, encouraging strict adherence to biosecurity and hygiene measures. Several countries, including Taiwan and the Philippines, have issued or extended travel advisories for Southeast Asia and select areas in the...

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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Welcome to Avian Flu Watch: Global H5N1 Tracker. Today, we offer a scientific, data-driven update on the global battle with highly pathogenic avian influenza H5N1.

Worldwide, the H5N1 virus continues to pose a grave threat, disrupting poultry production and crossing into new species and regions. According to the World Health Organization, as of April 2025, there have been 973 confirmed human H5N1 cases and 470 deaths in 25 countries – a fatality rate of 48 percent. Outbreaks since 2020 have surged due to the rapid global spread of clade 2.3.4.4b, affecting birds, mammals, and occasionally humans.

Let’s break down the latest regional hotspots and case numbers. In North America, the US West Coast remains a primary epicenter among cattle, with mathematical modeling from Nature indicating high herd positivity rates in California, Oregon, and Washington through late 2024 and early 2025. Arizona and Wisconsin now stand at heightened risk. In Mexico, the first fatal human H5N1 case was recorded in April 2025. Canada saw its latest severe human case in late 2024; British Columbia experienced mass outbreaks among poultry.

In South America, Brazil declared multiple states of emergency since 2023 due to wild bird outbreaks and continues intense surveillance across major poultry regions. The Pan American Health Organization confirms that by May 2025, 14 countries and territories have reported outbreaks in animals, especially in the Americas.

Across Asia, China remains a hub with routine detection of H5N1 in live poultry markets along migratory bird flyways, notably in Jiangsu, Shandong, and Henan provinces. Southeast Asia saw fresh clusters in Cambodia and Vietnam, with Cambodia reporting three fatal human cases in early 2025.

Europe has recently seen new human infections in the UK and persistent outbreaks in poultry. The Middle East data highlights Turkey and Lebanon as crossroads for cross-border transmission in birds, further linked to genetic flows between Egypt and Israel.

Visualizing trend lines, H5N1 cases in poultry and wild birds have surged since late 2023, peaking in early 2024 in the US and China, then oscillating as containment strategies took partial effect, illustrated by steep rises and intermittent drops in ‘Our World in Data’ case curves. Comparative statistics show that clade 2.3.4.4b dominates global outbreaks, but reassortant strains are emerging, including hybrids in Southeast Asia with genes from older lineages, raising concerns over future adaptability and transmission.

Analysis of cross-border transmission reveals wild bird migratory flyways, trade routes in poultry, and movement of livestock as the main factors in viral spread. Interventions like testing cattle prior to export in the US, and poultry export bans in the Philippines and other nations, have had some effect but succeeded only in partially quelling transmission. Migratory birds continue to seed new outbreaks across continents, evidenced by cases in Antarctica, the Arctic, and the Americas.

Notable containment successes include swift culling campaigns in the US and emergency operations in Brazil. However, failures are apparent in regions where surveillance lags or biosecurity measures remain insufficient, such as continued livestock outbreaks in US dairy herds and recurring farm infections in South and Southeast Asia.

Emerging variants of concern include the bovine-origin US strains showing divergence from East Asian bird-origin viruses, and the Greater Mekong Subregion’s recent hybrids which mix genes from multiple global clades. These may complicate future vaccine and diagnostic efforts.

Travel advisories currently recommend heightened avoidance of live poultry markets in Asia, restriction of handling sick or dead birds, and compliance with local health and agriculture advisories for travelers to outbreak zones. Animal health agencies urge...