the first case of this strain of h5n1 was detected in farmed geese in china’s southern guangdong region. southern china is unique ecologically and has been designated a putative influenza epicenter. it has many bodies of water, intensive farming systems, a highly dense human population, and is a dynamic industrial setting. the area is also an important wintering location for many migratory birds.

in the spring of 1996 several outbreaks of h5n1 occurred in farm geese at sanshui, a small town about 50 miles west of the capital of guangdong province. there was more than 40% mortality in the farmed geese. typical symptoms of infected geese included bleeding and neurological dysfunction.

by 2005 the virus had spread over to wild birds in a major way and new strains started to emerge. by 2020, it was believed that the viral strain was being sustained in wild bird populations year round. it is now said to be endemic in the migratory wild bird population.

wild birds are believed to have spread the virus worldwide. in 2021 hpai h5n1 hit north america. by 2022 it was in south america. it is believed to have never left the area. all continents have now been affected. in february 2024 it was found in antarctica. australia and new zealand held out the longest. this appeared to be because the migratory birds passing through these countries are shorebirds or waders (e.g., sandpiper plover, herons, egrets, flamingos, ibises, etc.) which are not as susceptible to hpai as waterfowl like ducks and geese. most recently however, australia has had cases of h5n1 hpai. new zealand, therefore, remains the only area without a known case of hpai. according to the new zealand government, however, they remain vigilant.

(https://www.mpi.govt.nz/dmsdocument/62035/direct)

according to the world organization for animal health (woah), wild bird migrations are believed to be the key long-distance carriers of the virus, it is the domestic poultry farms that can amplify it in an area. this reinforces the need for strict adherence to biosecurity programs on all poultry farms worldwide.

h5n1 hpai is now considered panzootic because it has spread to many different mammalian species. twenty-one species in the usa along have been affected. this includes mink, grizzly bears, fox, a polar bear, and an american marten (species of mammal in the same family as weasels, sea otters, and wolverines). scavengers and marine mammals were the first hit, and hit hard. there have been mass die offs of seals and seal lions. tens of thousands have died from quebec, canada to chile, argentina, and peru. 3500 sea lions died off peru’s coast, all infected with avian influenza.

world wide, at least 26 different mammalian species have been affected. in denmark millions of positive farmed mink had to be culled after the hpai virus spread through their fur farms. in canada free-ranging bears have been found to be infected. in france a captive bear was infected.

in some cases, it is not clear where the virus arrived from. mink in spain became sick with h5n1 even though no poultry outbreaks were reported in the region. mink, like swine, can become infected with both avian and human influenza viruses, with the threat of developing mixed strains of both.

new variants of h5n1 evolved in domestic poultry and went back into wild birds with deadly consequences. breeding colonies of sea bird species are most at risk.

in the summer of 2021 an h5n1 variant struck nesting seabirds on the shetland islands of  scotland. ninety percent of the adults in a breeding colony of great skua died.

this was followed by a massive mortality events of barnacle geese, gannets, gulls and terns elsewhere in europe. eight thousand common cranes died in israel. in north america, there has been significant mortality in gulls and eiders (canada is a major source of eider down) in new england  and of murres and gannets along the atlantic coast. in western africa great white pelicans as well as royal and caspian terns have had massive morality. in southern africa, there has been high mortality among the african penguins and cape cormorants. in india, flocks of demoiselle crane have been affected and in japan, hooded cranes.

in march 2024 usda confirmed h5n1 hpai in diary cows in texas and kansas. the virus is of the eurasian lineage goose/guangdong clade 2.3.4.4b. some infected heifers were shipped to other states before the outbreak was confirmed. to date 104 dairy farms in 13 states have become infected. it has also spread to dairy goats. cats drinking milk from infected cows have also become ill.

mortality has been low in the infected dairy herds (< 2%) with symptoms including thickened and discolored milk, low appetite, and reduced milk production. only about 10% of cows in a herd show signs of illness.

four alpacas on a farm in idaho tested positive for h5n1. the farm had recently depopulated an hpai-affected poultry operation.

what is the human risk?

the hpai virus most effectively infects birds since it is an avian influenza virus. however, the influenza virus is notorious for its high propensity to adapt, mutate, and combine with other influenza viruses to form new subtypes. the h5n1 virus has mutated and spilled over into other species, especially mammals. but what about people? is hpai the next pandemic like covid-19. researchers say that is unlikely.

scientists at mrc-university of glasgow centre for virus research (cvr) have identified a gene in human airways that stops us from being infected with avian influenza. the gene has been given the label btn3a3 and it blocks avian influenza viruses from replicating in the cells of our airways. there are, however, some strains of hpai that can evade this gene. the spanish flu of 1918 is thought to have been an avian influenza virus and it resulted in 25 million deaths. genetic mutations in hpai viruses have also resulted in btn3a3 resistant virus strains.

the strain of hpai that infected 1500 people in 2013 with a 40% mortality rate was an h7n9 strain of the virus and not an h5n1.

it is important to remember that the term ‘highly pathogenic’ for hpai refers to chickens and not to other species, including mammals.

poultry and dairy farm workers as well as slaughter plant workers are at the greatest risk because of the higher levels of exposure compared to the general public. contact with sick birds (or cows), or with their droppings, saliva, or feathers are the biggest risk factors. the poultry and milk products available on the market have been found to be safe, with no h5n1 contamination.

a few dairy farm workers have become infected with hpai, presumably from infected cows. the symptoms have not been life threatening and included mainly eye inflammation.

implementing biosecurity measures is a must. a developed plan on paper is not effective unless all staff strictly follow the measures it includes. the biosecurity plan must include covering the waste piles, and reporting any illness in the flock as soon as they are suspected. keeping good feed and water consumption records as well as accurate mortality records are all critical for early disease detection. in a previous outbreak, a drop in water consumption was the first symptom identified.

if you find dead wild birds on or off your farm, they should be left alone and untouched. report them immediately to the ky department of fish and wildlife toll-free at 1-800-858-1549.

the us department of fish and wildlife has more information on avian influenza on their website at https://www.fws.gov/avian-influenza.

uk leads program to train veterinarians in backyard chicken flock care | college news (uky.edu)