WASHINGTON, CMC – The Pan American Health Organization (PAHO) says avian influenza A(H5N1) continues to circulate in the Americas, with new outbreaks in birds and mammals and sporadic human infections linked to exposure to the virus.
It said Clade 2.3.4.4b, the region’s predominant strain since 2021, continues to drive the activity recorded in recent years.
Recent data indicate that 19 countries and territories have reported 5,136 animal outbreaks since 2022.
According to the latest epidemiological update report, since mid-October, 73 additional outbreaks have been recorded, primarily in domestic and wild birds. In 2025, nine countries reported 508 bird outbreaks, along with thousands of wild-bird detections, especially in the United States and Canada.
PAHO said 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, affecting more than 1,000 herds.
PAHO said the detection of the virus in non-avian species—including dairy cattle—underscores the need to consider livestock and wildlife surveillance in light 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, and the UN organization said that 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.
It said 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, and PAHO said that 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 (OIE), it is clear that the threat goes beyond the poultry sector.
Since 2003, the WHO has received reports of 991 human H5N1 cases, with a case-fatality rate of 48 per cent, 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 is also emphasizing 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 that the virus can be transmitted to humans through the consumption of properly cooked poultry products and stresses the importance of robust detection, reporting, and response mechanisms to address new outbreaks or suspected cases.
Avian influenza is caused by specific subtypes of the Influenza A virus, which primarily affect birds but 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 aquatic birds are the main reservoir and can transmit the virus to domestic poultry, leading to outbreaks that impact animal production.
Avian influenza viruses are also classified into genetic clades, which represent evolutionary lineages defined by specific mutations in their genome.
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