Above: Aedes aegypti, one of the species of mosquito that spreads dengue fever (James Gathany, Wikimedia Commons)

You’ve probably gotten a mosquito bite before. So you know that mosquito bites can cause red, itchy bumps. But is that all that mosquito bites can do?

Disease vectors

Mosquitoes are known as disease vectors because they can carry diseases from one animal to another. When a mosquito bites a human who has an infection, the mosquito gets the virus as well. The mosquito can then transmit this virus to any other people it bites. However, mosquitoes don’t experience any symptoms from the diseases they carry.

Did you know? Mosquito bites swell up and itch because your body has an allergic reaction to the mosquito saliva.

Dengue fever

Specific types of mosquitoes transmit specific diseases. For example, dengue fever is usually transmitted by Aedes aegypti and Aedes albopictus. These two species belong to the genus Aedes. In fact, only mosquitoes that belong to this genus can spread the disease.

People don’t experience symptoms until four to ten days after being bit by a dengue-carrying mosquito. About 400 million people contract dengue each year in tropical and subtropical areas, especially Africa, Southeast Asia, and the tropical Western hemisphere. However, only a quarter of these people experience symptoms.

The risk of contracting dengue fever from a mosquito in areas where disease-carrying species are rare is very low. There aren’t any Aedes aegypti or Aedes albopictus mosquitoes in Canada. So, if you're camping in the Canadian wilderness and get a mosquito bite, you likely won’t get the disease as a result!

Zika virus

Aedes aegypti is also the primary vector for the Zika virus. This species is an aggressive daytime biter, so it bites more people and has more opportunities to transmit disease. Different mosquitos also like biting different types of animals. Over time, Aedes aegypti has come to prefer biting mammals—including humans! Finally, these mosquitoes are very common because they only require a very small amount of water—less than three centimetres!—to lay their eggs in.

As of 2016, a Zika virus outbreak has spread to 24 countries. The World Health Organization has declared it a public health emergency for those countries. Some common Zika symptoms—like fever, rash, joint pain, and headaches—don’t sound all that bad.

However, Zika has also been linked to microcephaly in newborns and Guillain-Barré syndrome in adults. Microcephaly is a birth defect that causes babies to have small heads and brains. Guillain-Barré syndrome is a condition causing muscle weakness and paralysis.

Did you know? Only female mosquitoes bite people and animals. They need the nutrients in blood to produce their eggs.

West Nile virus

West Nile virus is a disease that mosquitoes carry from birds to humans. It is spread primarily by the Culex and Culiseta genera of mosquitoes. It’s most prevalent in Europe and Africa, but there have been outbreaks in North America as well.

The first case of West Nile virus identified in Canada was in a dead bird found in 2001. Since then, the number of people infected has changed from year to year. This might be because of changes in the weather, since mosquitoes prefer warmer weather. When there are cool summers or especially cold winters, there will be fewer mosquitoes to pass on diseases like West Nile virus.

While you’ll find lots of them in Canada during the summer, mosquitoes thrive in warm climates year-round. This explains why so many cases of mosquito-transmitted diseases occur in places close to the equator.

However, with temperatures rising around the world due to climate change, mosquitoes will eventually be able to live areas that used to be too cold for them. As mosquitoes like Aedes aegypti increase their range, the diseases that they carry could spread, too.

Malaria

Malaria is caused by parasites that mosquitoes pick up from infected humans and pass on to other humans through saliva. The parasites migrate to a person’s liver and into their bloodstream, destroying blood cells.

There are four parasites that can cause malaria. However, only one family of mosquitoes that can transmit the disease—Anopheles mosquitoes. Ninety per cent of malaria-related deaths happen in Africa, in areas south of the Sahara desert. This is partly because one parasite, Plasmodium falciparum, is very common there.

Malaria was eliminated in Canada in 1950. The risk of catching malaria in Canada is very small because we have very few Anopheles mosquitoes. The malaria parasite is also better suited to warmer climates. This means the only ideal time for malaria to develop and spread in Canada is during the summer.

Did you know? It would take over a million mosquito bites to drain all your blood!

So although many diseases that can be spread by mosquitoes, not all mosquitoes carry disease. You can keep most mosquitoes at bay by wearing long-sleeved shirts and pants, and by using mosquito repellent or mosquito nets. Whether you’re on vacation in the tropics or camping a bit closer to home, be sure to take precautions—even if it’s just to avoid being itchy!

Learn More!

About mosquito-transmitted disease:

Climate Change and Vector-Borne Disease
UCAR Center for Science Education

Mosquito Diseases
Mosquito World

Mosquito Transmitted Diseases
Connecticut Mosquito Management Program

About Zika virus:

About dengue fever:

Dengue – Epidemiology (2014)
Centers for Disease Control and Prevention

About West Nile virus:

West Nile Virus (WNV) (2014)
Minnesota Department of Health

Vector-Borne Diseases (2014)
Public Health Ontario

About malaria:

Malaria – Frequently Asked Questions (2015)
Centers for Disease Control and Prevention

Once bitten, twice shy: Malaria in Canada (2014)
K. Cholmondeley, CurioCity by Let’s Talk Science

Will a new vaccine help eradicate Malaria? (2014)
K. Cholmondeley, CurioCity by Let’s Talk Science

Brittany Smale

 


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