Global H5N1 Avian Flu Outbreak Intensifies: Cambodia Leads with 14 Cases, Worldwide Transmission Raises Alarm in 2025

This is Avian Flu Watch: Global H5N1 Tracker, your scientific window into the global spread of highly pathogenic avian influenza as of September 2025. Let’s begin with an overview of current hotspots and case statistics. Cambodia is now the global epicenter of human H5N1 cases this year, accounting for 14 infections and 8 deaths. According to CDC reports, clusters have been identified in Siem Reap, Takeo, Prey Veng, and Kratie provinces, with nearly all cases tied to direct contact with infected poultry or wild birds. India follows with 2 deaths, and Mexico has reported 1 fatal human case, a three-year-old child who died in April. The United States has detected 3 human cases early in the year, but none since February—though concern remains high due to H5N1’s endemic presence in birds nationwide, especially near large poultry and dairy operations. Zooming out, the World Health Organization records 26 human H5N1 infections worldwide from January to August 2025, 11 of them fatal. Since tracking began in 2003, there have been 972 confirmed global cases, with a striking 48% case fatality rate according to the European Centre for Disease Prevention and Control. Notably, no sustained human-to-human transmission of H5N1 has been verified. Visualizing trend lines, southeast Asia’s curve shows a sharp spike driven by Cambodia’s outbreak. Surveillance in North and South America reveals ongoing endemicity in wildlife and domestic flocks, with avian cases and spillovers detected across 32 U.S. states, over 115 wild bird outbreaks, and major events from Peru to Chile. The Americas have seen 76 human infections since 2013. In South America, recent genome mapping shows the North American Eurasian H5N1 lineage spread south in 2022, dispersing from Peru and Chile into Argentina, Brazil, Uruguay, and Ecuador. By contrast, Colombia and Venezuela have experienced separate introductions with limited onward transmission. Cross-border transmission remains a persistent challenge: in the United States, H5N1 has leapt from birds to mammals, including dairy cattle, with 17 states reporting infected herds as of June 2025, and more than 976 dairy herds affected overall. In 2025 alone, 56 cases have been confirmed in dairy cattle in California, Arizona, Nevada, and Michigan. The virus has also shown north-to-south mobility in South American wild birds and marine mammals, often following natural migratory pathways and local animal trade networks. Containment efforts show a mixed picture. United States animal health authorities have rapidly culled infected flocks and imposed movement restrictions, keeping further human cases low. However, Cambodia’s containment is hampered by limited rural health infrastructure and live bird markets, leading to more community clusters. In South America, coordinated surveillance between Peru, Chile, and neighboring countries has curbed some onward spread, but new introductions continue to challenge regional cooperation. Emerging variants of This content was created in partnership and with the help of Artificial Intelligence AI.