It’s easy for the tiny mosquito to fly under the radar. But its ability to rapidly spread deadly and disabling diseases to humans like malaria, lymphatic filariasis, Zika, West Nile virus, chikungunya, yellow fever, and dengue make it an incredibly dangerous adversary.
In honor of World Mosquito Day, we broke down 10 facts about the world’s deadliest animal, and the important work being done to defeat the diseases it transmits.
While dissecting the stomach tissue of a mosquito on August 20, 1897, Sir Ronald Ross discovered the malaria parasite inside. He soon proved that the female Anopheles mosquito is the animal responsible for transmitting malaria. Now, August 20th is known as World Mosquito Day to commemorate Sir Ronald Ross’ pivotal discovery. We now know that several Plasmodium species transmitted by mosquitoes can cause human malaria. Plasmodium falciparum malaria—the deadliest—is most common in sub-Saharan Africa, where it causes more than 400,000 deaths a year, the majority of whom are children under five.
Though only female mosquitoes feed on humans, the mosquito remains the deadliest animal in the world. Even today, the mosquito is responsible for over 1 million deaths each year. In addition to spreading deadly diseases like malaria, yellow fever, and dengue, these small insects can have a big impact on a person’s health and wellbeing. For example, mosquitoes spread the parasites that cause lymphatic filariasis (LF), one of the world’s leading causes of disability. Also known as elephantiasis, LF causes swollen limbs, severe pain, and social discrimination among millions of the world’s most vulnerable people.
A Vietnamese man who suffers from lymphedema caused by lymphatic filariasis walks with his grandchildren. Vietnam eliminated lymphatic filariasis as public health problem in 2018, allowing a healthier future for the next generation. Photo by Nguyen Minh Duc for RTI International
They may all look the same while buzzing around your head, but many of the more than 3,000 mosquito species are harmless. The most dangerous mosquitoes are certain species of Anopheles, Aedes and Culex—Aedes aegypti alone spreads LF, Zika, dengue, yellow fever, and more. The Anopheles mosquito, which is the main spreader of malaria in tropical and sub-tropical climates, can be found virtually everywhere except Antarctica. However, many mosquitoes don’t even consume human blood. The largest non-blood sucking mosquitoes on earth belong to the Toxorhynchites species, also known as the elephant mosquito. The larvae of Toxorhynchites eat the larvae of other mosquitoes, making them beneficial to humans.
Mosquito-borne diseases like malaria were extremely common in the United States before stagnant water breeding grounds for mosquitoes were paved over or drained, a practice we now call vector control. One famous figure that survived malaria was George Washington, who suffered from nine deadly diseases throughout his life. Before the disease was eliminated in the U.S. in 1951, seven other American presidents contracted the disease. Due to the threat that malaria posed, the Communicable Disease Center (CDC) was created. Today, about half of the world’s population lives in an area where a mosquito bite could lead to malaria, the majority in low- and middle-income countries.
The bed net is an invention that dates to antiquity, with various mentions across geographical regions. It is rumored that Cleopatra, the last pharaoh of Egypt, slept under a mosquito net. However, it wasn’t until the invention and testing of the insecticide-treated net (ITN) in the late 1980’s—which combined the physical barrier of nets with the repellent and mosquito-killing effects of insecticides—that bed nets became a viable preventive tool against malaria and other mosquito-borne diseases. Worldwide, treated bed nets were responsible for two-thirds of the seven million lives saved from malaria between 2000 and 2015, and are seen as a cornerstone of malaria prevention and control efforts. Through the USAID StopPalu and StopPalu+ projects in Guinea, RTI has supported the distribution of more than 10.5 million ITNs to communities at risk.
Imam Kerfalla Camara hangs the bed net he received through the mass bed net distribution campaign led by USAID StopPalu+. As voices of authority in their villages, religious leaders like Imam Camara play an important role in encouraging people to correctly and regularly use bed nets to prevent malaria. Photo by Patrick Adams for RTI International
Mosquitoes are starting to become resistant to the insecticides we use to fight them. The continued effectiveness of interventions against mosquito-borne diseases relies on our knowledge of local mosquito species, their host-seeking behavior, and their susceptibility to the insecticides being used. Through the USAID Okoa Maisha Dhibiti Malaria (OMDM)/Save Lives, End Malaria activity in Tanzania, we routinely monitor the susceptibility of mosquitoes to the insecticides in ITNs as well as those used to spray homes throughout mainland Tanzania and Zanzibar, including measuring how long clothianidin, a newer insecticide, remains on different surfaces after they’ve been sprayed. RTI researchers are collecting similar data from our work in Guinea that will help fill the gaps in our knowledge of the characteristics of local mosquitoes carrying malaria.
Teams in Zanzibar breed mosquitoes in the lab to test the effectiveness of different insecticides before they are used for household spraying. Photo credit: RTI International/Louise Gubb
We all dread the buzzing sounds that can spoil an otherwise pleasant evening outdoors. But some of our teams are pulling the night shift to better understand mosquitoes and the parasites they transmit. In order to collect information about biting behavior, abundance, seasonality, and distribution, malaria teams use a variety of techniques to collect mosquitoes, including light traps and even using themselves as human bait. And just like the mosquitoes that carry them, the bloodborne parasites that cause LF tend to be easier to find in a person’s blood at night. That’s why health officials often go door to door in the dark for these “night blood surveys” to detect the presence of LF in an area.
Theodor Seuss Geisel, better known as the children’s author Dr. Seuss, joined the U.S. Army during World War II as a captain and commander of the Animation Department of the First Motion Picture Unit. One of Geisel’s works during this time focused on preventing malaria from spreading through U.S. troops after Germany blocked the Allies’ supply of antimalarial drugs. In the pamphlet, Geisel warns of “Blood thirsty Ann,” a play on the Anopheles mosquito, who is out to drink G.I. blood and spread malaria.
Image by Theodor Geisel/Courtesy of USDA
We need globally available data to understand patterns and factors that increase or decrease risk of infection from mosquito-borne disease. In a recently published article, our teams analyzed data from 13 countries supported through USAID’s NTD programs and found that areas with lower elevation required more years to achieve success in eliminating LF, likely due to the presence of more mosquitoes. In collaboration with researchers around the world, we contributed to the first global, high-resolution map of P. falciparum malaria mortality, prevalence and incidence since 2010, which will help malaria programs better target high burden areas. These types of geospatial analysis help us identify the factors contributing to disease transmission and adapt interventions to the areas most in need.
Globally, we are making incredible progress against both malaria and LF. Groups like the Global Fund to Fight AIDS, Tuberculosis and Malaria, the President’s Malaria Initiative (PMI) and the Bill & Melinda Gates Foundation have played a large part in recent global progress against malaria, with the number of malaria-related deaths falling by 31% from 2010 to 2019. Thanks to an ambitious global effort, 17 countries and territories have now eliminated LF from within their borders. The U.S. plays a major role in this success story; since 2006, USAID has supported countries to distribute donated LF-fighting medicines ensuring that more than 315 million people are no longer at risk for the disease. Currently, USAID’s Act to End NTDs | East program, is helping 11 countries cross the finish line and wipe out LF by 2030.
