National Emerging Special Pathogens Training and Education Center
netec.org
H5N1 Outbreak Worst in U.S. History
Highly Pathogenic Avian Influenza A(H5N1), a strain of what is often referred to as bird flu, is responsible for a worldwide outbreak in poultry and wild birds. The current outbreak is the worst in United States history: more than
60 million birds have either died as a result of bird flu virus infection or have been culled due to exposure to infected birds.
Evolution of H5N1 Bird Flu
H5N1 was first detected in China in 1996 in domestic waterfowl, and the first human cases emerged during a poultry outbreak in China and Hong Hong in 1997 with 18 cases and six deaths. The virus re-emerged in 2003, causing poultry outbreaks across Asia, and around 2005 wild birds began spreading H5N1 to poultry in Africa, the Middle East, and Europe. Over the years,
new versions of the virus emerged globally in wild and poultry populations, until the H5N1 virus belonging to clade 2.3.4.4b became the dominant virus circulating at the end of 2021.
Human Infection with H5N1
H5N1 is highly contagious among birds and has a near 100 percent case fatality rate. However human infection is rare and mainly affects those with close contact to birds, including poultry farm workers or those with smaller flocks at home.
Since 2003, there have been
868 cases of human infection with H5N1 reported, of which 457 were fatal—a 53 percent case fatality rate. One
case of avian influenza A(H5) was reported in the United States in April 2022, in a person who had direct exposure to poultry presumed to be infected with H5N1.
Ecuador reported its first case on January 9, 2023, in a 9-year-old girl who had contact with backyard poultry.
H5N1 Spillover to Mammals
While H5N1 viruses mainly affect avian species, virus spillover into mammalian species has been reported. In January 2023, Montana Fish, Wildlife & Parks confirmed that
three grizzly bears tested positive for avian influenza; and the U.S. Department of Agriculture has
reported the virus in more than a dozen mammal species in the last year.
Cases of H5N1 in mammals are typically attributed to direct contact with sick or dead birds infected with H5N1. However a
study released last week describes the likelihood of transmission between mink at a farm in Spain, raising concerns about the
potential for human infections.
Caring for Patients with H5N1
H5N1 is considered a special pathogen, as we do not have effective medical countermeasures to prevent or treat infection. Prompt
identification of a suspected case of H5N1, isolation, and supportive care measures are essential. Additionally, there may be evidence for the
use of the antiviral treatment oseltamivir, which is used for other influenza A viruses.
Bird flu began spreading in late 2021.
money.yahoo.com
Bird flu continues alarming global spread
Bird flu continues alarming global spread
In late 2021, experts
sounded the alarm on the rapid spread of H5N1 or the avian flu. By April 2022, experts
warned the virus was "rapidly becoming a global concern."
In January, 2,500 endangered seals were found dead along the coast of the Caspian Sea in Russia. AFP says some early samples show at least some seals tested positive for avian flu, but authorities have yet to confirm the cause of the die-off.
All mammals tested positive for the PB2 mutation.
Europe is in the midst of its worst H5N1 outbreak on record, while South and North America have been hard hit. In Canada, about
200 flocks encompassing roughly 3.5 million birds had been infected as of November 2022.
Globally, tens of millions of birds have been culled due to infection or exposure.
Migratory birds are responsible for some of the recent outbreaks, creating the potential for additional cases when birds return to Canada for the summer.
Bird flu can be fatal for some domesticated birds, including chickens, ducks, and turkeys. It is possible to transmit H5N1 to humans, but cases are rare.
Experts say. ) H5N1 would have to mutate significantly to spread to humans.