H5N1 Avian Flu Spreads Across Wild Birds, Poultry, and Marine Mammals Worldwide

H5N1 Avian Flu Surges Across Wild Birds, Poultry Farms, and Marine Mammals

A dangerous new reassortant strain of H5N1 avian influenza is spreading rapidly. Scientists, wildlife officials, and veterinary authorities across multiple continents are tracking its expansion. The virus has now infected wild birds, farmed poultry, and marine mammals. Human cases have also been recorded, raising urgent public health concerns.

A New Genotype Emerges in North America

High pathogenicity avian influenza A(H5N1) clade 2.3.4.4b viruses entered North America in late 2021. They reassorted rapidly with local avian influenza viruses already circulating in the region. In September 2024, researchers detected a new reassortant strain. Scientists later classified this strain as genotype D1.1.

Researchers used both active and passive surveillance across Canada and the USA. They tracked D1.1 viruses spreading through wild bird populations during the 2024 fall migration. Phylodynamic analysis confirmed that D1.1 viruses formed a distinct monophyletic group. This new genotype displaced earlier A(H5) strains across several migratory flyways.

The toll on North American wildlife has been severe. Nearly 14,500 wild bird detections occurred in the USA alone. Mammal detections reached approximately 650 in the same country. Canada recorded HPAI infections across 12 taxonomic orders and 80 wild bird species within the first year of introduction.

The poultry industry has suffered enormously as well. Outbreaks affected more than 2,000 US flocks and 186 million birds. Canada reported more than 14.5 million birds affected across 534 flocks in all provinces. These figures highlight the devastating economic and agricultural impact of the virus.

Human Cases Linked to the D1.1 Strain

Authorities confirmed 17 human A(H5N1) infections linked to genotype D1.1. Four of these cases were classified as severe or fatal. Researchers examined the viruses collected from human patients closely. They found mammalian-adaptive genetic markers in the human case samples.

Crucially, researchers did not find those same markers in wild bird viruses. This distinction offers some reassurance about the current risk level in wild bird populations. Candidate vaccine viruses retained antigenic cross-reactivity with D1.1 strains. This finding suggests that existing vaccine development efforts remain on track.

The emergence of D1.1 also coincided with detections in dairy cattle. Scientists continue to monitor all these spillover events carefully. The virus’s ability to jump between species remains a central concern. Public health authorities are watching developments closely.

Nepal Battles Outbreaks Across Multiple Districts

Nepal is managing a significant H5N1 outbreak affecting multiple regions. Authorities identified 23 poultry farms hit by the virus by late March. More than 113,000 poultry had already been culled as a containment measure. The virus returned after an eight-month hiatus, detected again in early March.

Cases spread across four districts in the country. Sunsari district suffered the most, recording 12 separate outbreaks. Morang followed with eight outbreaks, while Jhapa reported two and Chitwan one. Authorities at local, provincial, and federal levels coordinated their response efforts.

Officials destroyed eggs, feed, and other potentially contaminated materials. Bird owners affected by culling operations will receive up to 75% compensation for their losses. Authorities identified wild birds as the likely source of the virus. The location of farms near sites that attract wild birds, poor farm biosecurity, and unregulated movements of people, vehicles, eggs, and live poultry exacerbated the situation.

The most recent report to the World Organisation for Animal Health put the outbreak total at 22. Directly impacted birds through mortality or preventative culling exceeded 142,000. Nearly all infected premises sat within Koshi province, the southernmost region. That area lies close to the border with India.

South Korea and the Philippines Face Escalating Crises

South Korea’s veterinary agency confirmed 21 additional poultry outbreaks to WOAH. These outbreaks began between February 6 and March 31 and covered six provinces. More than 2.55 million commercial birds tested positive for the H5N1 serotype. The scale of infection underlines the virus’s rapid spread through commercial operations.

South Korea also reported five confirmed outbreaks involving the H5N9 serotype. Those outbreaks led to the death or destruction of 1.07 million farmed birds since December. Since the first cases of the year were confirmed in mid-September, more than six million birds have been affected. A total of 56 premises recorded infections during this period.

In the Philippines, authorities are managing ongoing HPAI outbreaks at 10 poultry farms. These farms span three separate regions across the country. The Department of Agriculture’s bureau continues to monitor and report on the situation. The Philippines outbreak adds further pressure to the regional response effort.

Elephant Seals on the US West Coast Show Signs of Recovery

California’s Año Nuevo State Park in San Mateo County reopened to visitors after six weeks of restricted access. An H5N1 outbreak had killed more than a dozen elephant seals at the park. Field researchers from UC Santa Cruz and UC Davis detected the disease in late February. This marked the first detection of that H5N1 strain in elephant seals on the West Coast.

Scientists previously discovered the virus in seals in Maine in 2022. A major die-off of seals in Argentina in 2023 involved the same strain. These earlier events made researchers particularly vigilant about California’s seal colony. Roxanne Beltran, a professor at UC Santa Cruz, said her team ramped up monitoring after birds at the park tested positive.

As of April 2, the outbreak confirmed 32 cases in elephant seals in San Mateo County. Four additional cases appeared in Santa Cruz County. Two sea lions in San Mateo County and one in San Luis Obispo County also tested positive. One otter in San Mateo County tested positive as well.

Recovery at Año Nuevo Offers Cautious Optimism

At least 18 animals died from the virus, including at least 16 elephant seals. Park ranger Ziad Bawarshi confirmed that no new cases appeared for approximately two weeks. Parks officials reported that the virus had subsided enough to justify reopening. Officials noted that restrictions could return if new mammal cases emerge.

Visitors can now view the seals from established observation posts overlooking the beach. Most non-breeding adult seals have already migrated north to the Aleutian Islands in Alaska. Female seals remain at the park and are preparing to molt. Pups too young to migrate are still developing at the site.

The global spread of H5N1 across species and continents demands continued vigilance. Surveillance programs remain the first line of defense against further escalation. Scientists stress that early detection saves both animal and human lives. International coordination will prove essential in managing this evolving threat.