Mosquito bites are a part of Canadian living. Usually, the only consequence of an unwanted invasion is an itchy welt. However, over the last decade, the consequences have become significantly greater due to the emergence of several viruses.
In Canada, however, the risk for a mosquito-borne virus is quite low. We have no need to fear of Zika, dengue, and chikungunya, all of which have made headlines over the last few years. But one virus has made it to the Great White North and its presence has led to illness, hospitalizations and death.
The culprit is known as West Nile virus, or WNV. As the name implies, this virus was first isolated in Africa in the 1930s. Since then, it has managed to travel around the world, eventually reaching Canada in 2002. Today, the virus can be found in several areas of the country where mosquitoes tend to thrive.
Usually, when WNV attacks, a person doesn't notice as here are no symptoms. Some people will have to deal with fever, headache, swollen lymph nodes, and possibly a rash. The real trouble happens in people with weakened immune systems.
In immunocompromised individuals, the virus can enter the nervous system leading to a variety of troublesome symptoms such as confusion, muscle weakness, and stiff neck. The virus may be able to continue its journey into the brain. When this happens -- and it is quite rare -- a person facing a life or death situation due to swelling of the brain.
Despite the rather concerning nature of the virus, researchers managed to find a bright side to infection. Once a person cleared the infection, the virus would never cause troubles again. This discovery helped to lessen the impact of the virus in the country and by 2004, the worry of a WNV outbreak had calmed.
But then something happened in 2007. Instead of only a few cases, the number rose into the thousands. This revealed something about the virus few had thought possible at the time. Like other viruses known to circulate such as the flu and the common cold, WNV could evolve to avoid the immune system.
This ability to adapt concerned researchers. They had to find out how this virus was evolving and whether it could be stopped. Thankfully, there were only two options. Either the virus was adapting in the mosquito or inside the host, such as a bird or a human. The answer, however, remained a mystery.
Now, thanks to a group of American researchers, we know how this type of evolution happens. They have discovered a two-step process in which mosquitoes and their hosts contribute to the development of emerging strains. Based on the results, birds, animals, and even humans may be deciding, quite unsuspectingly, which WNV strains may thrive.
The tests in this study were relatively simple. The researchers collected various saliva samples from mosquitoes and examined them at the genetic level. Several different strains were identified as expected. But there was a surprise in store.
Instead of a single set of strains, each mosquito made and transferred an entirely different group of viruses. Evolution was happening completely at random and every newly developed virus had a chance to emerge. But deciding which ones were going to spread had nothing to do with the mosquito. That part of the evolutionary equation was dependent on the host.
Once the various strains entered the host -- in this case, birds -- the viruses unable to fight against the immune system ended up dying off. Only those with the ability to survive the host environment grew in number. The better adapted strains could spread and eventually emerge with future mosquito bites.
This process, known as purifying selection, is not uncommon in viral evolution. But it usually happens in the same infected individual. In this case, the mosquito is a constant source of new strains while the host ends up being the biological decision-maker.
The worst part of this phenomenon is the inability to control it. Only eradicating mosquitoes would stop this type of evolution from occurring, As we have learned over the years, this is simply impossible.
There is of course, a way to ensure you don't contribute to the emergence of new WNV strains. Simply don't get bit. Whether you choose long clothing, insect spray containing DEET, or choose when to go outside, reducing the chances for a bite inevitably helps. While it may not be considered the best way to enjoy the spring and summer weather, it may be the safest for you and due to this evolutionary mechanism, for everyone else.
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