In April, a new strain of H1N1 flu virus hopped from a pigs into people. This event sparked a pandemic that is now estimated to have killed 115 people and infected more than 17,000, according the World Health Organization. In the first video ever posted on Science of the Times, we explore how flu viruses can jump species.
TRANSCRIPT:
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The flu virus can infect all kinds of animals from ducks to chickens, pigs, humans and even whales.
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But scientists think that flu viruses in all of these animals, originally came from aquatic birds, like ducks.
DUCK:
Quack!
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So how can a flu virus jump species, from birds, to other animals and ultimately to humans?
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To answer this question,we need to look at the structure of the virus and how it survives.
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Influenza is an RNA virus, meaning that it’s filled with strands of RNA,a genetic material similar to DNA. The outside of the virus is coated in proteins.
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In order to infect a cell, the virus must dock up and deliver it’s RNA. A protein on the outside of the virus, known as hemagglutinin, sticks to receptors embedded in the cell’s outer membrane.
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Once inside the cell, the viral RNA goes to work, co-opting the cell’s own molecular machinery in order to replicate itself and create proteins that will form new viruses. These new viruses, known as virions, disperse and infect other cells.
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Humans CAN contract flu viruses from birds, but this rarely leads to an infection. The receptor proteins in birds and humans are different ENOUGH that the virus can’t easily dock to a cell.
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However, viral RNA is not static. During replication, errors can accumulate and these can change the hemaglutinin protein just enough. Now the bird virus can infect the cells of other creatures, including humans.
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But typically, that other creature is the humble pig. A pig’s cells have both the human-type and bird-type receptors. This means that both bird AND human flu viruses can infect a pigs cells. In other words, pigs act as a kind of viral middleman.
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And it’s no coincidence that most flu pandemics of recent years are thought to have originated in South East Asia, where people often keep pigs and birds in close proximity.
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What’s more, is that inside of a pig, flu viruses can become more infectious. Cells infected with both bird and human strains of influenza become incubators for new viral strains. The RNA can reshuffle, which could lead to new viruses with the worst traits of the two original strains.
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Flu vaccines are a defense against viral infection. They stimulate antibodies against the proteins on the virus’ surface. This prevents it from docking and unloading its RNA.
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But as long as the flu virus survives SOMEWHERE, in pigs for example, it can mutate again, changing its outer proteins and a newly infectious strain is born.
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