Welcome to Avian Flu Watch: Global H5N1 Tracker. This week, we deliver a data-driven briefing on the state of highly pathogenic avian influenza, or H5N1, and its evolving impact across continents.

H5N1 continues to pose a major global biosecurity threat. Since 2020, the virus has been reported in every continent except Australia, with especially severe outbreaks in the Americas, Asia, and Europe. As of April 2025, the World Health Organization has tracked 973 human cases worldwide, with a 48 percent case fatality rate, underscoring the gravity of zoonotic transmission.

Let’s break down the current hotspots. In the Americas, the U.S. remains the primary epicenter for H5N1 activity. Modeling published by Nature in January 2025 indicates that most U.S. outbreaks are concentrated in the West Coast states, with Arizona and Wisconsin facing significant risk of emerging outbreaks. The dairy sector, which experienced its first H5N1 outbreak in cattle in early 2024, continues to grapple with persistent transmission. In the past year, over 20 million chickens were culled in the U.S., leading to supply shortages. Mexico and Canada have both recorded their first pediatric fatalities linked to H5N1 in early 2025, with sustained infections traced to domestic poultry and wild birds.

Elsewhere, Southeast Asia remains a major concern. Cambodia reported three pediatric deaths linked to H5N1 from January through March 2025, each tied to direct contact with infected poultry. India has also recorded a fatal human case this year, while China continues to monitor both avian and mammalian spillover, including notable cross-infections in cattle and wild mammals. Europe’s major poultry producing nations, including the United Kingdom and France, are maintaining vigilance with regular outbreaks among poultry and sporadic cases in farm workers and domestic animals.

For listeners seeking a visualization, imagine a world map: red hotspots dotting the U.S. West Coast, deepening through Mexico, and radiating through Southeast Asia and China. Trend lines published by regional authorities and health organizations show upward curves in confirmed animal cases in early 2025, though the pace varies based on local containment efficacy. For instance, while U.S. cases plateaued briefly in spring, inadequate biosecurity at cattle farms and gaps in interstate animal movement testing have led to recurring flare-ups.

Cross-border transmission remains a defining feature of the epidemic. Migratory pathways of wild birds connect continents, spreading H5N1 from breeding grounds in Asia to the Americas. The virus has also been documented in marine mammals along South American coasts, with records from Argentina estimating 600,000 wild birds and 50,000 mammals lost to the virus since 2022.

Containment efforts have had mixed results. Brazil’s rapid declaration of a health emergency in response to its first outbreaks allowed authorities to avert mass poultry losses, a relative success. In contrast, the U.S. dairy and poultry industries continue to struggle with detection and farm-level intervention, highlighting the challenge of controlling a virus so well-adapted to animal hosts and so mobile via global trade networks.

Emerging variants are under close watch. Cambodia’s recent human cases reveal a mix of longstanding clades and newer hybrids carrying internal genes from the highly transmissible 2.3.4.4b lineage, raising concern for potential adaptation to human infection.

Travel advisories remain fluid. The WHO and CDC continue to recommend that those travelling to areas with active outbreaks avoid contact with live poultry or wild birds, and closely monitor health symptoms after return.

Thank you for tuning in to Avian Flu Watch: Global H5N1 Tracker. Join us again next week for the latest data and analysis. This has been a Quiet Please production—for more, visit QuietPlease...