WASHINGTON, USA, (PAHO) – The Pan American Health Organization (PAHO) reported that avian influenza A(H5N1) continues to circulate in the Americas, with new outbreaks detected in birds, mammals, and sporadic human infections linked to exposure to the virus. Clade 2.3.4.4b—the region’s predominant strain since 2021—continues to drive the activity recorded in recent years.
Recent data indicates that 19 countries and territories have reported 5,136 outbreaks in animals since 2022, according to the epidemiological update released yesterday. Since mid-October, 73 additional outbreaks have been recorded, primarily in domestic and wild birds. In 2025, nine countries have confirmed 508 outbreaks in birds, along with thousands of wild bird detections, especially in the United States and Canada.
The geographic spread and high frequency of outbreaks in poultry and wild birds continue to challenge biosecurity and food production across the region.
The update also notes ongoing activity in mammals. Canada and the United States have reported 77 outbreaks in wild and domestic mammals so far this year. Since March 2024, the United States has detected infections in dairy cattle in 18 states, with more than 1,000 herds affected. The detection of the virus in non-avian species—including dairy cattle—underscores the need to consider livestock and wildlife surveillance, according to the context of risk and epidemiological patterns.
PAHO reports that human cases remain rare. Since 2022, the Americas have reported 75 human H5N1 infections, with two deaths. In 2025, three cases occurred in the United States and one in Mexico. Additional zoonotic influenza infections include one human case of A(H5N2) in Mexico and one human case of A(H5N5) in the United States—the latter representing the first A(H5N5) infection reported globally.
These recent human cases highlight the importance of early detection through epidemiological, virological, and genomic surveillance—both human and animal—to identify any changes in the virus, as well as timely clinical management and contact tracing. Most cases have been associated with direct contact with infected animals, with no evidence of person-to-person transmission.
Globally, since 2020, clade 2.3.4.4b of H5N1 has caused extensive mortality in birds across Africa, Asia, and Europe and later spread to North, Central, and South America. Mammalian outbreaks have been identified across three continents.
With the virus now detected in 22 countries on three continents, including mammal outbreaks reported in the Americas to the World Organization for Animal Health (WOAH), it is clear that the threat goes beyond the poultry sector. Since 2003, WHO has received reports of 991 human H5N1 cases, with a case-fatality rate of 48 percent, in 25 countries worldwide.
PAHO, in collaboration with WOAH and FAO, urges countries to strengthen animal and human surveillance in affected areas; reinforce biosecurity protocols; enhance intersectoral coordination; and ensure integrated analysis of epidemiological and virological data.
Countries are also urged to actively monitor populations at higher risk of exposure—including poultry and backyard farmers, veterinarians, farm workers, and those involved in wildlife management—to identify early clinical signs such as respiratory illness, conjunctivitis, or neurological symptoms. PAHO also emphasises the need to enforce strict biosecurity measures and the appropriate use of personal protective equipment (PPE) in farms, laboratories, and health facilities.
The update reiterates that there is no evidence the virus can be transmitted to humans through the consumption of properly cooked poultry products, and stresses the importance of having strong detection, reporting, and response mechanisms in place for new outbreaks or suspected cases.
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