Washington, DC, November 25, 2025 (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 related to exposure to the virus. Clade 2.3.4.4b, the predominant strain in the region 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 published yesterday. Since mid-October, 73 additional outbreaks have been recorded, mainly in domestic and wild birds. In 2025, nine countries have confirmed 508 outbreaks in birds, along with thousands of detections of wild birds, 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 domestic and wild 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, highlights the need to consider surveillance of livestock and wildlife, depending on the risk context 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. Other zoonotic influenza infections include a human case of A(H5N2) in Mexico and a human case of A(H5N5) in the United States; The latter represents the first A(H5N5) infection reported worldwide.
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 human-to-human transmission.
Globally, since 2020, H5N1 clade 2.3.4.4b has caused major mortality in birds in Africa, Asia and Europe and has then spread to North, Central and South America. Outbreaks have been identified in mammals on three continents.
Now that the virus has been detected in 22 countries on three continents, including outbreaks in mammals reported in the Americas to the World Organization for Animal Health (WOAH), it is clear that the threat extends beyond the poultry sector. Since 2003, WHO has received reports of 991 human cases of H5N1, with a case fatality rate of 48%, in 25 countries around the world.
PAHO, in collaboration with WOAH and FAO, urges countries to strengthen animal and human surveillance in affected areas; reinforce biosafety protocols; improve intersectoral coordination; and ensure the integrated analysis of epidemiological and virological data.
Countries are also urged to actively monitor populations at highest risk of exposure (including poultry and backyard poultry farmers, veterinarians, agricultural workers, and those involved in wildlife management) to identify early clinical signs such as respiratory illnesses, conjunctivitis, or neurological symptoms. PAHO also emphasizes the need to enforce strict biosafety measures and the appropriate use of personal protective equipment (PPE) on farms, laboratories and health facilities.
The update reiterates that there is no evidence that the virus can be transmitted to humans through consumption of properly cooked poultry products and emphasizes the importance of having robust detection, notification and response mechanisms for new outbreaks or suspected cases.
avian influenza virus
Avian influenza is caused by certain subtypes of the influenza A virus, which primarily affect birds, although they can occasionally infect mammals, including humans. These viruses are classified into subtypes based on their surface proteins (hemagglutinin (H) and neuraminidase (N), such as H5N1 or H5N2. Wild waterfowl are the main reservoir and can transmit the virus to domestic birds, causing outbreaks that affect animal production.
Avian influenza viruses are also classified into genetic clades, which represent evolutionary lineages defined by specific mutations in their genome. Currently, the H5N1 clade 2.3.4.4b predominates in the Americas and has been responsible for the most recent outbreaks in birds and mammals. Genomic surveillance is key to detecting viral changes that may affect spread, severity, or the ability to infect new species.
