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

Bird flu has tightened its grip on birds and mammals across the Americas, but for now it appears to have hit a ceiling in people.

A new epidemiological update from the Pan American Health Organization (PAHO), released March 11, finds that highly pathogenic avian influenza A(H5N1) is now firmly established in bird populations from Canada to Argentina and has spilled into at least 37 mammal species. Yet human infections remain rare: 75 confirmed cases and two deaths since 2022, with no new human cases reported in the region since late 2025.

The report, which compiles official outbreak data through March 9, paints a picture of a virus that has become a structural problem for farms, wildlife and coastal ecosystems, but has not evolved the ability to spread easily among people.

“Available 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 agency said.

Virus entrenched in birds

Between early 2022 and early 2026, 21 countries and territories in the Americas reported 5,744 H5N1 outbreaks in birds and mammals to the World Organisation for Animal Health.

Those outbreaks span industrial poultry farms, backyard flocks and wild species. Since January 2025, H5N1 has been detected in 94 bird species in 11 countries and territories, from migratory waterfowl to seabirds and domestic chickens.

Recent data show a notable shift. By mid-2025, detections in wild birds had begun to decline, while outbreaks in domestic birds—especially poultry—became more prominent.

In December 2025 alone, health and agriculture authorities reported 97 H5N1 outbreaks in avian species to the animal health agency. Ninety-six of them were in domestic birds, including 75 in the United States, 15 in Canada, five in Colombia and one in Brazil. Only one outbreak was in wild birds.

From January through March 9 of this year, 105 additional avian outbreaks were reported in the region, 95 of them in domestic birds. The United States again accounted for most of the domestic outbreaks, while Argentina, Chile and Uruguay reported the bulk of wild bird detections.

The pattern underscores how H5N1, once primarily seen as a disease sweeping through migratory flocks, is now a recurring threat inside barns and backyards.

A growing list of infected mammals

Alongside the entrenchment in birds, the virus continues to jump into mammals.

From January 2025 through early March 2026, H5N1 was detected in 37 mammalian species in the Americas, most of them in the United States and Canada. In 2025 alone, 218 outbreaks in mammals—wild and domestic—were officially reported to the global animal health agency.

Those detections have included dairy cattle, foxes, skunks, bears, marine mammals and domestic cats. In early 2026, Canadian authorities confirmed H5N1 in a striped skunk in Ontario, while U.S. officials documented further infections in dairy herds and wildlife through national surveillance.

The animal health agency has classified high pathogenicity avian influenza in cattle as an “emerging disease.” International bodies including the World Health Organization and the U.N. Food and Agriculture Organization have urged countries to test bulk milk in high-risk areas and to promote pasteurized milk.

Despite the expanding mammal tally, experts say there is no sign so far that the virus is transmitting efficiently within mammal populations or changing in ways that make it more likely to spread between humans.

Human cases stall

On the human side, the new report suggests a plateau.

From April 20, 2022, to March 9, 2026, five countries in the Americas reported 75 laboratory-confirmed H5N1 infections and two deaths. The United States accounts for 71 of those cases, including a man in Louisiana whose death was announced by the Centers for Disease Control and Prevention in January 2025. Mexico, Canada, Chile and Ecuador have each reported one H5N1 case.

Four human H5N1 infections were recorded in the region in 2025—three in the United States and one in Mexico. Since late November 2025, however, no additional human H5N1 cases have been reported in the Americas.

Most infections in the region have occurred in people with direct, unprotected exposure to infected animals or contaminated environments, such as poultry workers, dairy farm employees and backyard flock owners. Many U.S. cases have presented with mild illness, though severe disease and death have occurred.

Other avian influenza subtypes have also appeared in humans. Mexico confirmed a human infection with H5N2 in October 2025 in a person exposed to backyard poultry and other birds at home. In November 2025, U.S. officials reported the world’s first known human infection with H5N5, a fatal case in an individual with underlying conditions and exposure to backyard poultry. Health authorities found no evidence of onward transmission in either event.

Globally, from 2003 through Jan. 26, 2026, the World Health Organization has received reports of 993 human H5N1 cases and 477 deaths, a case-fatality proportion of 48%. Many of those cases occurred in earlier waves and different viral clades.

While that high global fatality ratio feeds recurring fears of a “bird flu pandemic,” health officials in the Americas continue to stress that the current risk to the general public remains low.

One Health, surveillance and undercounts

Public health and animal health agencies say that low risk depends heavily on sustained surveillance.

PAHO is urging countries to strengthen monitoring at the human–animal interface, especially among agricultural workers, veterinarians, poultry cullers, health care workers and laboratory staff.

The organization recommends that clinicians and health authorities be alert for respiratory illness, conjunctivitis, unexplained encephalitis or clusters of severe acute respiratory infection in people with recent exposure to birds, mammals or affected environments, or who have traveled from areas with known outbreaks.

Suspected human cases should be sampled and tested promptly at National Influenza Centers or other reference laboratories, the agency says. Under the International Health Regulations, countries are required to notify the World Health Organization immediately of any suspected or confirmed human infection with a novel influenza A virus.

On the animal side, PAHO and its partners call for intensified surveillance in poultry, wild birds, pigs and dairy cattle, with risk-based sampling and rapid reporting of outbreaks to the global animal health organization. They also recommend robust biosecurity on farms to limit contact between domestic animals and wild birds.

Officials acknowledge that the numbers in the latest report likely understate the true extent of infection in wildlife, backyard flocks and remote areas, where carcasses are harder to find and diagnostic capacity is weaker. Economic and political pressures—including fears of trade restrictions or hits to tourism—can also make some countries reluctant to report outbreaks quickly.

Food, wildlife and what comes next

Beyond the immediate animal health concerns, the spread of H5N1 carries broader economic and ecological costs.

Over the past two decades, outbreaks of highly pathogenic avian influenza have led to the loss of hundreds of millions of poultry worldwide through death and culling, affecting egg and meat supplies and smallholder incomes. In the Americas, the recent concentration of outbreaks in domestic birds raises the prospect of recurring production shocks and trade disruptions.

The virus has also devastated wildlife in some areas. The global animal health agency has warned that H5 viruses are causing “increased mortality in wildlife and ecological disruption worldwide,” including in colonial seabirds and marine mammals. In South America, mass die-offs of seabirds and South American sea lions have put additional pressure on vulnerable species and forced coastal communities and governments to manage large numbers of infected carcasses.

International organizations have begun pushing a new strategy that leans more on vaccination and improved biosecurity and less on mass culling alone, but implementation varies widely by country.

For now, health authorities say the best protection for most people is straightforward: avoid direct contact with sick or dead birds and mammals, do not drink raw milk, and handle and cook poultry and eggs properly.

While human infections remain sporadic and limited to those with close animal contact, officials warn that the virus’s continued circulation in birds and mammals gives it more opportunities to change.

As PAHO put it, as long as H5 viruses are entrenched in animal populations, “additional human infections among exposed individuals are anticipated,” even if the overall risk to the wider public stays low.