Influenza is classified into three types, A, B and C. All other flu infections of type A are listed by subtypes. Influenzas grouped in to B and C types are not that common, so subtypes have not been identified.
Listing human influenza viruses involves identifying the virus type and making vaccines for the population to prevent massive outbreaks. Influenza is a killer and historically is responsible for millions of deaths around the planet.
The types of common influenza strains vary each year and that is the reason vaccine production may be delayed until the exact strain is identified. H1N1 and H3N2 have made the rounds of the world population over the last few decades.
With the invention of modern technology to track historic flu strains, scientists have tracked modern strains with roots in history. Samples taken from the victims of the 1918 Flu Pandemic show that the flu strain was a variation of the modern H1N1 strain.
Bird flu, also known as Avian Influenza, can be low pathogenic or grow into high pathogenic epidemics, depending on the type of genetic makeup. Human forms of the disease include h7N3 and H7N7 and can be transferred to humans who regularly work with birds, although infection is a rare event.
Swine flu is a type of influenza that infected pigs, but the virus shifted from pigs to humans, a close biological relative. The virus was first contracted by a human working with pigs and migrated to the human population. Other animals contracting flu include horses, the H7N7 and H3N8 viruses, and dogs, the H3N8.
The Hong Kong Flu was first identified from a carrier located in Hong Kong and created a new way of popularly identifying flu strains.
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