PAHO: H5N1 Spreads Widely in Animals Across the Americas, but Human Cases Remain Rare

By now, the virus has turned up in sea lions off Chile, backyard flocks in Mexico and dairy cattle from Texas to Wisconsin. Since 2022, it has driven more than 5,700 outbreaks in birds and mammals across 21 countries in the Americas. Yet the latest regional data show the number of confirmed human infections with this strain of avian influenza, H5N1, still stands at just 75.

The Pan American Health Organization’s new update on avian influenza A(H5N1), released March 11 with data current through March 9, describes a virus deeply entrenched in wildlife and on farms but only sporadically detected in people. No new human H5N1 infections have been reported in the Americas since late November, even as fresh outbreaks continue in poultry and wild birds.

Health officials say that gap is a sign that H5 viruses remain primarily animal pathogens. Some researchers say it may also reflect whose illnesses get counted — and whose do not.

A panzootic across the Americas

The report, which serves as the World Health Organization’s regional snapshot for the Americas, confirms that highly pathogenic H5N1 has been detected in birds and mammals in every subregion since it arrived with migratory waterfowl in 2021 and 2022. From epidemiological week 2 of 2022 through week 9 of 2026, 21 countries and territories notified the World Organisation for Animal Health of 5,744 outbreaks.

This year alone, from Jan. 1 to March 9, veterinary authorities in Argentina, Brazil, Canada, Chile, the United States and Uruguay reported 105 new outbreaks in avian species. Ninety-five involved domestic birds such as commercial poultry, and 10 involved wild birds. No mammal outbreaks have been officially reported to the animal health body so far in 2026, though the update notes hundreds of mammal infections in 2024 and 2025, including widespread disease in U.S. dairy cattle.

Human infections: few, mostly linked to animal exposure

On the human side, the numbers look very different.

Between April 20, 2022, and March 9, 2026, five countries in the region — the United States, Mexico, Canada, Chile and Ecuador — reported a total of 75 confirmed human H5N1 infections and two deaths. The United States accounts for 71 of those cases, including one person infected after poultry exposure in 2022 and 70 cases recorded between March 2024 and February 2025, largely among dairy and poultry workers.

Most of those U.S. patients had mild illness, such as conjunctivitis or upper respiratory symptoms, and all recovered, according to national and international health agencies. There has been no documented sustained human-to-human transmission.

The other cases in the region were more severe. Ecuador reported the Americas’ first H5 infection in a person in January 2023, a 9-year-old girl with exposure to backyard poultry who developed critical illness but survived. In March 2023, Chile confirmed an adult case in the northern Antofagasta region after contact with sea lions and wild birds; that patient also survived.

Canada detected a single H5N1 infection in November 2024. Mexico reported its first human H5N1 case, a 3-year-old girl from Durango state, in April 2025. She later died of respiratory complications.

In addition, Mexico has identified two human infections with a related virus, H5N2, one of them fatal, and the United States reported the world’s first known human case of H5N5 in November 2025 in a Washington state resident who died after contact with backyard birds.

Despite those episodes, the overall picture in the Americas is one of rare, isolated infections in people against a backdrop of extensive circulation in animals.

“Available virological and epidemiological data indicate that influenza A(H5) viruses continue to remain avian influenza viruses, with no evidence of established adaptation to mammals or sustained human-to-human transmission,” the Pan American Health Organization wrote in the March 11 update.

At the same time, the agency warned that as H5N1 persists in wild and domestic birds and spills over into mammals, “additional human infections are anticipated,” particularly among people with direct exposure to infected animals and contaminated environments.

Is underdetection masking infections in workers?

The WHO’s most recent global assessment of influenza at the human-animal interface, published in December, described the risk of infection with H5 viruses as “low for the general population, low-to-moderate for exposed persons.” That phrasing has become standard in public messaging.

Some experts caution that the broad reassurance can obscure sharply higher risks for people working with infected animals and may downplay gaps in surveillance.

“I think we should assume there are infections that are occurring in farmworkers that just aren’t being detected,” said Jennifer Nuzzo, an epidemiologist at Brown University, in an interview last year about the spread of H5N1 in U.S. dairy herds.

Serologic surveys in dairy workers in states such as Michigan and Colorado have suggested that around 7% had antibodies to H5N1, indicating prior infection. Most of those workers were never diagnosed at the time, according to researchers involved in the studies.

Public health officials and labor advocates point to a familiar set of barriers: many agricultural workers are migrants or on temporary visas, lack health insurance and paid sick leave, and may fear that reporting symptoms or testing positive could threaten their jobs or immigration status. Language barriers and remote rural locations can further limit access to testing.

PAHO has urged countries to strengthen surveillance for influenza-like illness and severe acute respiratory infections among people with exposure to poultry, pigs, cattle and other animals, and to collect both respiratory and eye swabs from suspected cases while using appropriate protective equipment.

The agency also calls on clinicians to consider H5 infection in patients with pneumonia, acute respiratory distress, encephalitis or conjunctivitis who have had contact with sick or dead birds and mammals or who live in areas with known outbreaks.

Biosecurity, culling—and debate over vaccination

On the animal health side, authorities in the Americas have tightened farm biosecurity, expanded testing and, in some settings, ordered large-scale culling.

The U.S. Department of Agriculture confirmed H5N1 in dairy cattle in Texas and Kansas on March 25, 2024, and the virus has since been identified in more than 1,000 herds across 18 states. Federal orders issued in December 2024 and expanded in 2025 established a national milk testing strategy, including bulk-tank and processing-plant sampling, and movement controls for affected herds.

The USDA and the Food and Drug Administration have repeatedly said that pasteurization inactivates the virus and that the commercial milk supply remains safe. International agencies, including the World Health Organization and the Food and Agriculture Organization, echo that position and advise against consuming raw milk.

In the poultry sector, countries from Canada to Brazil have accelerated surveillance and, in some cases, debated or begun vaccination campaigns. Mass culling operations, such as a high-profile ostrich cull in British Columbia in 2025, have triggered disputes over animal welfare, compensation and transparency in how decisions are made.

Wildlife impacts and what’s changing about this wave

Beyond farms, the virus has had visible effects on wildlife. Since 2022, H5N1 has been linked to die-offs in seabird colonies and marine mammals on both coasts of the Americas. Conservation biologists warn that repeated waves of infection could push already vulnerable species closer to the brink and alter coastal ecosystems.

Globally, human H5N1 infections remain rare but severe when they occur. From 2003 through Jan. 26, 2026, the World Health Organization recorded 993 laboratory-confirmed cases of H5N1 in 25 countries, including 477 deaths, a case fatality proportion of about 48%. Those figures come largely from earlier waves of the virus in Asia and the Middle East.

The current panzootic is different in key ways. The dominant viruses, from a lineage known as clade 2.3.4.4b, have expanded their host range to hundreds of wild bird species and at least 68 mammal species worldwide. The jump into dairy cattle in the United States, with evidence of cow-to-cow transmission and distinct viral genotypes emerging, marks a new chapter in the virus’s ecology.

Public health agencies in the Americas are trying to stay ahead of those changes. PAHO, the Food and Agriculture Organization, the World Organisation for Animal Health and the World Health Organization now issue joint risk assessments, and PAHO runs an online dashboard tracking outbreaks in animals and humans across the region.

Countries are encouraged to share virus samples with WHO-affiliated laboratories to support risk analysis and the development of candidate vaccine viruses, part of broader pandemic preparedness plans built up since COVID-19.

The bottom line

For now, officials say the general public’s risk remains low. There is no sign that H5N1 has acquired the ability to spread efficiently from person to person, and the human case count in the Americas has not surged despite the virus’s spread in animals.

The question is whether that uneasy balance will hold — and whether health systems can detect and respond quickly if it starts to shift. As PAHO put it in its latest assessment, the continued circulation of H5N1 in birds and mammals means more human infections among exposed groups are expected. How many of those are seen, and how many remain invisible, may shape the region’s next chapter with this virus.