Over 48 mammal species infected with virus since 2020; threat of mutation that sustains human-to-human transmission
Photo for representation: iStock A bird flu outbreak in poultry in Andhra Pradesh’s Nellore district was reported on February 7, 2024. Laboratory tests by the National Institute of High-Security Animal Diseases in Bhopal confirmed that it was caused by the type A strain of the H5N1 variant of the avian influenza virus.
The bird flu cases were discovered in the villages of Chatagutla in Podalakur and Gummaladibba in Kovur district sub-divisions after several chicken deaths were reported on poultry farms. The disease did not emerge in commercial operations but was found in backyard poultry farms.
Hundreds of birds and eggs were culled on February 17, 2024 as per policy. A three-day ban was imposed on shops selling chicken within a 10-kilometre radius of the epicentre and a three-month ban on shops within a 1-km radius.
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The poultry likely caught the virus from migratory birds in Pulicat lake in nearby Tirupati district, according to officials. Migratory wild aquatic birds, particularly waterfowl, are the primary natural reservoirs for most subtypes of influenza A viruses, infecting poultry and other bird or animal species, according to the World Health Organization for Animal Health.
The virus is endemic in poultry populations in Asia, Europe and Africa. Rare cases of avian influenza with type A (H5N1) viruses have been identified in humans across Asia, Africa, the Americas and Europe. In 1997, an outbreak of human infections with the same strain was found in Hong Kong, China. Since 2003, 868 human cases and 457 deaths have occurred globally, indicating a 52 per cent death rate, according to the World Health Organization (WHO).
The emergence of influenza A viruses with the ability to infect people could potentially lead to a pandemic when the virus mutates to sustain human-to-human transmission that evades immunity, according to the global health body. How and when it will spread will be difficult to predict, WHO added.
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A recent study published in the latest edition of the journal Emerging Infectious Diseases said the avian influenza A virus subtype H5N1 has already been in a significant panzootic phase between 2020 and 2023, the equivalent of a pandemic in the animal kingdom. The researchers reviewed information on infected mammals from 59 scientific articles published between 2020–2023 and between 2003-2019, across two periods of infections
The paper underscored the risk that mammalian adaptation could pose for human health, emphasising that information is scarce on the current panzootic (2020-2023) event.
The virus that originally infected birds crossed over to several mammal species in 2003, affecting tigers, leopards, lions, pigs, minks, donkeys, foxes, domestic dogs and cats, bears and seals. Since 2020, the number of infected species has increased and has affected more than 48 mammal species, substantially larger than previous waves.
It is therefore of some conservation concern, however, large populations of animals have so far not been identified. The paper highlighted the incident of 20,000 South American sea lions who suddenly died, with several testing positive for H5N1, underlining the potential effect of this virus on some threatened mammal populations.
Read more: We should only worry about bird flu making us sick when we see human-to-human transmission
In the current period of infection (2020-2023), excluding humans, mammals in 26 countries have been infected by this virus: Europe (17 countries), South America (5 countries), North America (2 countries), and Asia (2 countries). The new geographic areas identified were Peru, Chile, and Argentina, where 13 marine mammal species, up to thousands, reported deaths.
There is no evidence of human-to-human transmission, however, mutations of the H5N1 virus could increase the risk of a pandemic, the paper warns. A case in point is the Spanish influenza (1918-1919) pandemic that developed from an avian influenza virus.
“For instance, the T271A mutation reported in minks in Spain is also present in the H1N1 that produced a pandemic in 2009. Similarly, the PB2-E627K mutation found in this virus in diverse geographic areas could indicate an adaptation for replication in mammals,” the report said.
“Mutations and infections with H5N1 in potential mixing-vessel species (for example, minks and wild and domestic pigs) should be followed closely because of the potential risk to human health,” the report added.
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Since 2018, the WHO has been bracing itself for a pandemic from an unknown illness termed “Disease X”. The unknown set of pathogens from which Disease X can emerge is large and beyond the influenza virus, but the origin is likely going to be zoonotic, according to the Johns Hopkins Bloomberg School of Public Health.
It could be arising right now, from any part of the world, according to scientists.
“There could be the first jumps of a virus into a human population somewhere and maybe 90 per cent of the people who get it have a common cold like illness, or what appears to be garden variety pneumonia, and nobody tests for that.” Amesh Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security said in an interview.
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