by Margaret Dedloff
When you think about the world’s deadliest animals, you might think about the Nile crocodile, responsible for an estimated 200 deaths a year, or hippopotamuses, responsible for around 500 deaths a year. However, the real deadliest animal in the world is one typically considered to be just a pest: the mosquito. Mosquitoes are responsible for over 700,000 human deaths per year.
Image of a mosquito on human skin. Image source.
There are around 3,500 species of mosquitoes in the world, and they can be found on all continents except Antarctica. All mosquitoes share a four-stage life cycle. The mosquito life cycle consists of egg, larva, pupa, and adult mosquito. Only adult female mosquitoes bite as they need blood to make eggs.
The mosquito life cycle. Image source.
When a mosquito bites you, while the mosquito takes a small amount of your blood, some of the mosquito saliva also enters into your body. Your immune system recognizes the saliva as something foreign, meaning it’s not part of your body. The immune system then produces histamine. Histamine acts like your body’s bouncer; it does its best to kick out whatever is invading. Similar to how histamine tries to get pollen out of your body in the springtime by making you sneeze, histamine tries to get the mosquito saliva out of your skin by making you itch.
While a typical mosquito bite might just be an annoyance, mosquitoes can carry deadly diseases that can be present in their saliva, and be given to a person when they are bit. The ability to transmit diseases is what makes mosquitoes the deadliest animals on the planet. There are tens of millions of cases of mosquito-borne illness each year. These diseases can be caused by viruses you may have heard of before such as chikungunya virus, dengue virus and yellow fever virus, or by parasites, like malaria.
Malaria is a mosquito-borne parasite that causes fever, chills, and flu-like illness. Malaria can develop into a severe disease that can lead to death. There were an estimated 241 million cases of malaria with 627,000 deaths in 2020 worldwide, making malaria one of the deadliest infectious diseases in the world. Malaria mainly occurs in Africa, South Asia, and Central and South America. Recently, there have been eight cases of malaria in the United States that have not been acquired by travel.
While malaria is the most prevalent mosquito-borne illness, there are other dangerous illnesses transmitted by mosquitoes. Dengue virus is known to have infected 5.2 million people in 2019. Zika virus can have severe complications for pregnant women and their fetuses. There was a major Zika virus outbreak in South America during 2015 and 2016. During this outbreak, an estimated 1.5 million people were infected in Brazil alone. All of these diseases make mosquitoes the deadliest animals.
Common mosquito-borne illnesses. Image made by author in BioRender.
But, there is good news! Since 2000, malaria deaths have decreased by half, likely due to better treatment and control of mosquitoes. Additionally, there have been new and innovative methods to decrease the mosquito population, like generating mosquitoes that kill other mosquitoes. There is also a TON of research being done on mosquito-borne illnesses, with malaria being an important research priority at the National Institute of Allergy and Infectious Diseases, and several labs studying mosquito-borne diseases at local universities, like the University of North Carolina at Chapel Hill. In fact, I study Zika virus! With all of the important work being done to better understand and prevent mosquito-borne illnesses, hopefully one day mosquitoes will just be annoying pests!
