NIAID Now | August 20, 2021
World Mosquito Day, recognized each year on August 20, marks the anniversary of the discovery that mosquitoes transmit the parasite that causes malaria. On this day in 1897, Sir Ronald Ross discovered the malaria parasite in the stomach tissue of an Anopheles mosquito. His work later confirmed that mosquitoes are the vector which carries this devastating parasite from human to human.
Today, more than 120 years later, mosquito-borne diseases are still both widespread and difficult to treat. Even with global efforts to curb their impact on vulnerable populations, mosquito-borne diseases cause hundreds of thousands of deaths each year. According to the World Health Organization, malaria alone leads to approximately 400,000 deaths annually. Other mosquito-borne diseases, even when non-fatal, can be devastating for patients. For example, Chikungunya causes crippling joint pain, and Zika infection in pregnant women can cause severe birth abnormalities. For many years, NIAID has supported research into these diseases and the mosquitoes that carry them and, even in the midst of the COVID-19 pandemic, this research has continued to yield valuable results. NIAID-supported researchers are developing control approaches which could protect against a wide array of mosquito-borne diseases, investigating potential ways to reduce or eliminate transmission of these diseases, and supporting research into therapeutics and vaccines to treat or prevent them.
The mosquito-borne disease with the greatest global impact is malaria. Plasmodium falciparum, the parasite responsible for the most prevalent and severe cases of malaria, is transmitted from person-to-person by Anopheles mosquitoes, which are widespread throughout tropical regions of the world. The malaria parasite relies on the mosquito’s unique biology to reproduce and jump between people: the mosquito first takes up the parasite while feeding on the blood of a person with malaria; over the next stages of its life cycle, the parasite migrates through the body of the mosquito, eventually infecting the mosquito’s salivary glands, from which it is injected into another person when the mosquito takes its next blood meal. Once in the human host, the parasite undergoes additional developmental stages in its complex life cycle, and the hallmark symptoms of intense fever and chills may appear. Malaria infection may also be accompanied by nausea and vomiting, headaches, muscle and joint aches, and fatigue. In cases of severe malaria, especially in vulnerable groups such as children and pregnant women, the disease can manifest as cerebral malaria with seizures or coma, or can cause severe anemia, respiratory distress, kidney and liver failure, cardiovascular collapse, shock, and death. Without the mosquito to function as an intermediary, the malaria parasite could not be transmitted between people.
The mosquito has a complex life cycle of its own. Though different species of mosquitoes prefer different places to lay their eggs, many Anopheles mosquitoes lay their eggs in undisturbed pools of water. The eggs hatch into aquatic larvae, which grow until they are ready to pupate into flying adults. Adult male and female Anopheles feed on nectar; the females are also required to feed on blood (resulting in what humans know as mosquito bites) as the nutrients in the blood allow the females to produce eggs, continuing the cycle anew.
Each of these mosquito life-stages offers an opportunity for disruption—and the potential for local reduction in malaria transmission. For instance, NIAID-supported researchers are studying the factors that drive adult mosquitoes to begin seeking a mate. In a paper published earlier this year, Wang et al describe how male Anopheles mosquitoes use light and temperature to determine what time they should begin forming their mating swarms. This is in contrast to some other insect species which rely on pheromones to drive their mating behaviors. Mating swarms are essential for reproduction in some Anopheles species as females must fly into the male swarm to become inseminated. By collecting mosquitoes from the wild as they rose to swarm at dusk and analyzing the genes that were activated in the mosquitoes’ heads, the researchers were able to identify specific “clock genes” that ensure male mosquitoes swarm at the same time and location each evening.
The researchers suggest that by understanding the environmental and genetic factors that trigger the formation of Anopheles mating swarms it may be possible to disrupt mating behavior to reduce mosquito populations—an important consideration since mosquitoes are becoming increasingly refractory to existing control measures. New technologies for battling mosquitoes and the diseases they carry are urgently needed. NIAID supports research on mosquito biology as well as approaches that target the malaria parasite such as antimalarials and malaria vaccines that could provide protection against infection.
For more information on NIAID-supported research on mosquitos, please see NIAID’s Vector Biology Program website: https://www.niaid.nih.gov/research/vector-bio
At NIAID, the Laboratory of Malaria and Vector Research conducts research on mosquitoes, along with many other disease vectors: https://www.niaid.nih.gov/research/lab-malaria-vector-research
To watch a video about mosquito research supported by NIAID, click here.