A cat walks among chickens.
Outbreaks have been seen in dozens of affected cats in Poland and South Korea, many with paralysis and seizures.
The increase in mammalian H5N1 cases is concerning because these outbreaks pose a continuing risk to humans.
Since 2022, at least 26 species of mammals have been affected by H5N1 in many countries on several continents.
Authorities in South Korea have reported an outbreak of H5N1 bird flu in shelters. cat In the capital Seoul. Thirty-eight of the shelter’s 40 cats died. Avian influenza has not been detected in cats in South Korea since 2016, although the subtype detected in 2016 was H5N6 rather than H5N1.
Also in recent days, 34 domestic cats in eight Polish provinces tested positive for the H5N1 avian influenza virus.Many infected cats have Neurological symptoms, such as paralysis and seizures. Of the 34 infected cats, 11 died from the infection and 14 had to be euthanized.
The increasing cases of H5N1 infection in mammals, including a recent case on a Finnish fur farm, is worrying because These outbreaks pose an ongoing risk to humanity.
To this end, the Food and Agriculture Organization of the United Nations (FAO), the World Health Organization (WHO) and the World Organization for Animal Health (WOAH) are urging countries to work together to save as many animals as possible and protect people.
Bird flu viruses spread between animal species
Preliminary genetic sequencing of viruses isolated from Polish cats indicated that they belonged to clade 2.3.4.4b of the H5N1 virus and were similar to viruses circulating in wild and poultry. The A/Goose/Guangdong/H5N1 avian influenza virus lineage first emerged in 1996 and has been causing outbreaks in birds since then. In 2020, H5N1 viruses of the highly pathogenic avian influenza (HPAI) 2.3.4.4b clade emerged from this circulating lineage.this clade It spreads to many parts of Africa, Asia and Europe mainly by migratory birds. They pose a threat to animal and human health worldwide.
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The current H5N1 avian influenza epidemic has led to outbreaks in poultry and an unprecedented number of wild bird deaths. Between October 2021 and December 2022, a total of 2,918 outbreaks in poultry and 378 in captive birds occurred in Europe, 4,480 wild bird infections were recorded, and 50 million birds were culled from affected farms. These viruses entered North America in late 2021 and then South America in the fall of 2022.
In 2022, 67 countries on five continents will report outbreaks of highly pathogenic H5N1 avian influenza in poultry and wild birds, which means that More than 131 million poultry died from infection or forced culling. In 2023, 14 other countries, mainly in the Americas, reported outbreaks. Since 2022, at least 26 species of mammals have been affected by H5N1 in many countries on several continents.
873 human cases reported over two decades
Thus, there appears to be a disturbing shift in the ecology and epidemiology of avian influenza, as the disease spread to new geographic areas, resulting in unusually high mortality rates in wild birds and an alarming increase in mammalian cases. . For example, in early 2023, more than 600 sea lions were found dead or dying on the beaches of Peru. This was the first mass extinction of wild mammals in South America due to H5N1 bird flu.They have been notified since December 11, 2021 There have been multiple human cases of H5N1 worldwide. The severity of human infection with the H5N1 virus ranges from asymptomatic or mild cases to severe and fatal cases. Globally, since January 2003, 873 cases of human infection with H5N1 avian influenza virus have been reported in 21 countries. from them, 458 people died, a mortality rate of 52%.
Viral sequences from these human cases, if available, did not show markers of mammalian adaptation or resistance to H5N1 antivirals such as oseltamivir and baloxavir.
Fortunately, Currently, the virus does not have the ability to easily bind to human upper respiratory receptors, meaning transmission is difficult.. The people most vulnerable to H5N1 infection are those who have close and regular contact, directly or indirectly, with birds (domestic, wild, or captive). For example, poultry farmers, veterinarians, slaughterers, infected farm workers, etc.
Another good news is that, so far, No human-to-human transmission detected. Unfortunately, based on available information, human immunity to clade 2.3.4.4b is expected to be minimal.
For the H5N1 virus to become a problem, and possibly even cause a human pandemic, it must improve airborne transmission among mammals, gain better entry into human cells, and effectively evade the human immune system.
virus mutation
Several mutations in the H5N1 hemagglutinin and RNA polymerase 2 (PB2) genes have been shown to facilitate airborne transmission among mammals. At least several mutations at the Q226L and G228S positions in the viral hemagglutinin are also known to facilitate H5N1 binding to the α2-6 sialic acid receptors of human cell membranes. Unfortunately, perhaps a small step has been taken, as some H5N1 viruses of clade 2.3.4.4b detected in mink in late 2022 have a rare mutation (T271A) in the PB2 gene, May facilitate infection in mammals including humans. Similarly, the E627K mutation in the H5N1 RNA polymerase PB2 gene was also found in virus samples from infected foxes and seals, and appears to promote viral multiplication in mammalian cells.
The highly pathogenic H5N1 virus is constantly changing, and the current multiple outbreaks increase the likelihood that humans have been exposed to the virus or adapted to other mammalian species that may serve as intermediate species. Therefore, we must not relax our vigilance and continue to do a good job in the prevention, monitoring, detection and control of current and possible future epidemics.