Zoonotic Influenzas
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Zoonotic influenzas spread around the world in yearly outbreaks, resulting in about three to five million cases of severe illness and approximately half a million deaths.
‘Zoonotic’ means they are caused by pathogens, in this case viruses, that have hopped from infected animals to humans.
They have been found in a variety of animals, like domestic poultry, wild birds, and pigs.
In humans, they typically cause mild to severe respiratory symptoms and fever, and they also have the potential to cause epidemics or pandemics.
Influenza viruses belong to the Orthomyxoviridae family.
They are segmented, negative sense, single-stranded RNA viruses.
Only types A and B cause disease in humans, with type A influenza viruses being the most common.
Influenza viruses are classified based on two surface proteins: hemagglutinin, or H protein, and neuraminidase, or N protein, of which there are many different types.
So for example, the H1N1 virus that causes swine flu has H protein type 1 and N protein type 1.
Among other things, these surface proteins determine what species the virus can infect.
However, influenza A viruses can undergo antigenic shifts where two strains of the virus mix their genome to create a new virus with a different set of H and N proteins.
This allows the new virus to infect different species from the original strains.
The most common types of zoonotic influenzas are avian, meaning originating from birds, and swine, meaning originating from pigs.
Avian flu is caused entirely by influenza A virus and transmission is often through direct contact with infected poultry as the birds are slaughtered or plucked.
Based on pathogenicity, avian influenza is divided into two types: high pathogenicity or low pathogenicity.
The type with the greatest risk is highly pathogenic avian influenza, or HPAI.
The most well-known HPAI strain is H5N1, which first appeared in China in 1996, and was then responsible for the bird flu outbreak in 2004.
Key Takeaways
Zoonotic influenza refers to the influenza viruses circulating in animals, and are also able to infect humans. These viruses can cause respiratory infections that range from mild to severe, and in some cases, they can lead to deadly pandemics. The most well-known zoonotic influenza virus is the H5N1 virus, also known as avian influenza or bird flu, which is primarily found in birds, but can occasionally infect humans who come into close contact with infected birds.
Other examples of zoonotic influenza viruses include swine flu (H1N1), which can be transmitted from pigs to humans, and the recently emerged COVID-19 virus, which is believed to have originated from bats. The prevention of zoonotic influenza transmission to humans includes careful monitoring of animal populations, avoiding contact with sick animals or their feces, and practicing good hygiene, such as frequent hand washing.