The science behind the scenes - Emerging infections: viruses that come in from the wild
Wild animals carry all sorts of viruses. Not only do these viruses harm animals, they can also spread widely between animal populations and can sometimes affect human health too. Viruses that we know affect humans, such as rabies, HIV and influenza, all originated in animals.
How does a virus move from an animal to a human?
Many viruses change their genetic code quite quickly and this allows them to adapt to new environments (such as a new animal host, or a human) with great speed. "Emerging viruses" are viruses that have recently spread into human populations. Most emerging viruses are animal diseases that have transferred to humans. Scientists are studying emerging viruses by:
- looking at natural infections in wildlife
- tracking how viruses become efficient at spreading between humans
- studying how viruses evolve (change their genetic code) even during a single human infection.
Common human diseases caused by viruses include the common cold, influenza (flu), chickenpox and cold sores. Many serious diseases such as Ebola, AIDS, avian influenza and SARS are also caused by viruses. Why do you think 'swine flu' was called 'swine flu'? Because it was a variety of a flu virus that crossed into humans from infected pigs.
If a virus usually found in wildlife is going to turn into an emerging infection in humans, certain conditions have to be right. Two processes have to occur:
- evolutionary processes - mutations to the genetic code of the virus
- ecological processes - overlap between human and animal populations, which might be caused by wildlife moving into human areas because their habitat is destroyed.
Scientists can follow the path that a virus has taken from its origins in animals to its current position as a human virus, and look at how it has changed and evolved along its route. They can sequence the virus to find out its genetic code at different stages of its evolution, which helps them understand how viruses adapt to become a danger to humans.
What is a virus?
A virus is a fragment of genetic material (DNA or RNA) covered in a protective protein coat. Viruses cannot survive on their own. They can only grow or reproduce inside a living cell – the host cell. Viruses invade living cells and use the cell’s chemical machinery to produce many new copies (replication). Viruses infect the body by turning living cells into virus factories so that viruses are passed into the surrounding tissue. They quickly pass between individuals in fluids, such as the water droplets in a sneeze, or in infected blood.
Viruses can mutate when they replicate, which means part of their genetic code changes. This can affect what sort of a protein coat they are contained in as well. If a drug has been designed to control a particular virus, it may be less likely to be effective against a virus which has undergone mutations in the part of the virus where the drug works. We call these 'drug-resistant' viruses.
Why is this important?
Go to main page of Teacher's Resource - Emerging infections: viruses that come in from the wild