H5N1 Bird Flu Spreads Globally: US Dairy Herds Infected, Cambodia Reports Highest Human Cases in 2025

This is Avian Flu Watch: Global H5N1 Tracker, your data-focused update on the worldwide spread of H5N1 bird flu. Let’s begin with the geographic hotspots. According to the US Centers for Disease Control and Prevention, Cambodia has reported fourteen human H5N1 infections so far in 2025, resulting in eight deaths. Seven of these cases are children. The viral clade in Cambodia—2.3.2.1e—has been endemic in poultry for years, but continues to spill over to humans. India reported two fatal human cases—one child and one adult—earlier this year; both had links to poultry, but no human clusters have emerged there. In North America, the Global Virus Network and CDC confirm an escalating crisis: H5N1 is now present in all 50 US states, across Canada, and has spilled into over 1,000 American dairy herds since 2022, marking an unprecedented expansion into mammalian hosts. Now let’s describe the trend lines. Visualize rising peaks on incident graphs throughout 2024 and 2025: the US shows the steepest climb, first in poultry, then cattle. Over 168 million poultry culled in the US and Canada underpin a relentless upward trend. Cambodia’s human case line remains low but persistent, with sharp local spikes. In India, the curve is flatter but worryingly creeping upward. A look at comparative statistics: In 2025, the United States reports over 70 human H5N1 infections, with its first recorded death and vast animal losses. In contrast, Cambodia’s 14 cases this year account for more than 45 percent of its total reported human H5N1 cases over the past three years. Globally, since 2003, over 800 human H5N1 infections have been documented, with a case fatality rate exceeding 50 percent, reflecting ongoing lethality. Turning to cross-border transmission, genomic analyses published in The Lancet and Nature highlight repeated viral movement across Eurasia and Africa. Turkey and Lebanon serve as regional hubs in the Middle East, where closely related viral genotypes have been identified in neighboring countries, revealing complex poultry trade and migratory bird connections. In the US, mathematical models from Nature Communications show that interstate cattle movement became a key risk after the virus entered dairy herds in 2024. Testing and cattle movement restrictions have curbed, but not stopped, spread. Containment success stories include Cambodia’s rapid clinician outreach and targeted education. These efforts have capped human-to-human transmission so far. In the US, swift federal movement controls on cattle exports slowed viral jumps between states, though the scale of livestock outbreaks shows major gaps remain. By contrast, failures are evident in under-resourced countries where delayed outbreak recognition and weak biosecurity have allowed undetected viral circulation. In terms of variants, 2025 brought a new H5N1 mutation in US cattle, dubbed D1.1, with genetic features suggesting recent avian-to-mammal adaptation. Its continued surveillance is critical, as This content was created in partnership and with the help of Artificial Intelligence AI.