Science Wiki

Mosquito-borne disease is an illness caused by a pathogen (a virus, a protozoan parasite, or a filarial nematode) that is transmitted to a vertebrate host by the bite of an infected mosquito. Only female mosquitoes feed on blood, because they need its proteins to develop eggs, so only females transmit disease. Mosquitoes are the most important group of arthropod disease vectors for humans. Mosquito-borne diseases include malaria, dengue fever, yellow fever, chikungunya, Zika fever, Japanese encephalitis, West Nile fever, Rift Valley fever, and lymphatic filariasis. Malaria is the main cause of death among them, with an estimated 250 million cases and about 600,000 deaths a year in recent World Health Organization (WHO) reports, most of them in children in sub-Saharan Africa. Dengue is the most widespread viral disease, with an estimated 390 million infections a year, of which roughly a quarter cause symptoms, and record numbers of reported cases in 2023 and 2024.

Mosquito-borne diseases are part of the larger group of vector-borne diseases, which the WHO estimates to account for about 17 percent of the global burden of infectious disease. The distribution of the diseases follows the distribution of their vectors, and so it responds to temperature, rainfall, land use, urbanization, trade, and travel. They are studied in epidemiology, medical entomology, virology, parasitology, and Earth system science.

Vector groups

Of the roughly 3,500 described species of mosquito (family Culicidae), only a few dozen are important vectors of human mosquito-borne disease. The three most important groups are the genera Anopheles, Aedes, and Culex.

Main mosquito vector groups

Several features of mosquito biology determine how well a species transmits disease. These are the preference for human blood (anthropophily), the biting rate, the daily survival of adults, the time and place of biting and resting, the ability of the species to support the development of the pathogen (vector competence), and the abundance of the vector. A species with a strong preference for humans, long adult life, and frequent biting is a more efficient vector than one with the opposite habits, even if the second species is more abundant.

Life cycle

Mosquitoes that transmit mosquito-borne disease have four stages: egg, four larval instars, pupa, and adult. The first three stages of most species are aquatic. Development from egg to adult takes about a week at 27 to 30 °C and much longer at lower temperatures. Females mate once or a few times, feed on blood, digest it, and lay eggs, and this cycle of feeding and egg laying (the gonotrophic cycle) is repeated several times in a life. Each blood meal is an opportunity for a female to acquire a pathogen from an infected host and, later, to transmit it. The length of the gonotrophic cycle (typically 2 to 4 days in warm conditions) sets the biting rate. Females find hosts by carbon dioxide, body odors, heat, and vision, and the relative weight of the cues differs among species.

Viruses

Most mosquito-borne human pathogens are RNA viruses, the arboviruses (arthropod-borne viruses), from four main families:

• Flaviviridae (genus Orthoflavivirus): dengue, yellow fever, Zika, Japanese encephalitis, West Nile, St. Louis encephalitis, Murray Valley encephalitis, and Usutu viruses.
• Togaviridae (genus Alphavirus): chikungunya, Ross River, Mayaro, o'nyong-nyong, Sindbis, and the equine encephalitis viruses (eastern, western, and Venezuelan).
• Peribunyaviridae and Phenuiviridae (order Bunyavirales): La Crosse and Jamestown Canyon viruses, and Rift Valley fever virus.
• A few viruses of other families, such as Batai virus.

Parasites

In parasitic mosquito-borne disease, the protozoan parasites of the genus Plasmodium cause malaria. Five species commonly infect humans: P. falciparum (the most lethal, and dominant in Africa), P. vivax (widespread outside Africa, with a dormant liver stage that causes relapses), P. ovale, P. malariae, and the zoonotic P. knowlesi (a macaque parasite that infects humans in Southeast Asia). The filarial nematodes Wuchereria bancrofti and Brugia species cause lymphatic filariasis, and Dirofilaria species cause heartworm disease in dogs and occasionally infect humans.

Diseases and vectors

Major mosquito-borne diseases

Some other arboviruses that infect people are not primarily transmitted by mosquitoes. The Oropouche virus, which caused large outbreaks in South America and the Caribbean in 2023 to 2025, is transmitted mainly by biting midges (Culicoides paraensis), and the role of mosquitoes in its transmission is minor and uncertain. Similarly, many Aedes albopictus and Culex infections found in field-caught mosquitoes show that a mosquito has fed on an infected host, and they do not by themselves show that it can transmit the virus.

Biological transmission

Mosquito-borne pathogens are transmitted biologically, which means that the pathogen multiplies or develops in the mosquito before it can be transmitted. A mosquito that takes a blood meal from an infectious host ingests the pathogen, and the pathogen must then complete development in the mosquito. For viruses, the steps are infection of the cells of the midgut, escape from the midgut into the hemolymph, infection of other tissues, and infection of the salivary glands, from which it is released in saliva during a later bite. The time from ingestion to the ability to transmit is the extrinsic incubation period (EIP). It is a few days for viruses such as chikungunya and about 1 to 2 weeks for dengue, and about 10 to 20 days for Plasmodium at typical tropical temperatures. The mosquito must survive this period, and, because mosquitoes in the field usually have short lives, this is a major constraint on transmission.

At each step, the mosquito has barriers (the midgut infection and escape barriers, and the salivary gland infection and escape barriers), and its immune system, including RNA interference, limits the replication of viruses. The ability of a mosquito population to become infected and transmit a given pathogen is its vector competence, and it varies among species, among populations of one species, among pathogen strains, and with temperature and the gut microbiota. Some viruses can also be transmitted from an infected female to her offspring (vertical or transovarial transmission), and a few can be transmitted between mosquitoes during mating, and these routes help viruses to persist through dry or cold seasons.

Temperature and extrinsic incubation

In mosquito-borne disease, the EIP shortens as temperature rises, because the development of pathogens depends on temperature. For Plasmodium falciparum, a classical degree-day model assumes that development needs a fixed amount of heat above a minimum temperature, of about 111 degree-days above about 16 °C:

where n is the EIP in days and T is the mean temperature in °C. At 25 °C, n = 111 / 9 ≈ 12 days. At 20 °C, n = 111 / 4 ≈ 28 days, which is longer than most field mosquitoes live, so that transmission is unlikely. At 30 °C, n ≈ 8 days. The model is a simplification, and it ignores the effects of daily temperature variation, but it shows why transmission is sensitive to small changes in temperature.

Quantifying transmission

The classical model of mosquito-borne disease transmission is the Ross-Macdonald model, developed from the work of Ronald Ross and George Macdonald. The vectorial capacity V is the number of potentially infective bites that result from a single infectious person per day, and the basic reproduction number R₀ (per generation of host to vector to host) can be written as:

where m is the number of female mosquitoes per human, a is the rate of biting on humans per mosquito per day, b is the probability that an infectious bite infects a human, c is the probability that a mosquito becomes infected after biting an infectious human, μ is the daily mortality of adult mosquitoes, n is the EIP in days, and r is the rate of recovery of humans. The factor e^−_μn_ is the probability that a mosquito survives the EIP. Several consequences follow:

• The biting rate appears as a², because a mosquito must bite twice (once to acquire and once to transmit the pathogen). A reduction of contact between people and mosquitoes, for example by bed nets, has a large effect, and R₀ in the square-root form is proportional to a.
• Mosquito density enters linearly in V and as a square root in R₀, so that halving the density reduces R₀ by about 29 percent.
• Survival has the largest effect. For μ = 0.1 per day and n = 10 days, e⁻¹ ≈ 0.37 of mosquitoes survive the EIP. If daily mortality is doubled to 0.2, the survival falls to e⁻² ≈ 0.14, and, including the change in the denominator, V falls by a factor of about 5. This is the reason that measures that kill adult mosquitoes are most effective against pathogens with a long EIP, such as malaria parasites.
• To eliminate transmission, R₀ must be brought below 1. A control measure with an effect E on transmission needs E > 1 − 1/_R_₀ in a simple model, so that for R₀ = 5, it must reduce transmission by more than 80 percent.

The models are simplifications. They assume a well-mixed population, constant parameters, and no immunity, and they do not describe heterogeneity in biting, seasonal changes, or the spatial spread of infection. More detailed models, including individual-based and spatial models, are used for planning. The same framework applies to the other vector-borne diseases, and the parameters differ among pathogens and vectors.

Transmission cycles

Mosquito-borne diseases circulate in distinct ecological transmission cycles:

• Anthroponotic cycles. The pathogen circulates between humans and mosquitoes only. Malaria (except P. knowlesi), urban dengue, urban yellow fever, chikungunya in epidemics, and lymphatic filariasis are of this type. Elimination is possible in principle by treating people and controlling vectors.
• Zoonotic and enzootic cycles. The pathogen circulates between mosquitoes and animals, and humans are infected as accidental hosts. In West Nile virus infections, birds are the amplifying hosts and humans are usually dead-end hosts, because the level of virus in the blood of humans is too low to infect mosquitoes. In Japanese encephalitis, pigs amplify the virus. In sylvatic yellow fever, monkeys and forest mosquitoes maintain the virus. Such cycles cannot be eliminated by treating humans, and the control relies on vaccination, vector control, and surveillance of animals.
• Bridge vectors. A mosquito that feeds on both animals and humans, such as some Culex and Aedes albopictus, can carry a virus from the enzootic cycle to humans.
• Spillover and urbanization. Viruses can move from forest cycles to urban cycles when infected people enter cities with Aedes aegypti, as happened in the yellow fever epidemic in Angola in 2015 and 2016.

Global burden

Mosquito-borne diseases cause substantial illness and death, and they are concentrated in the tropics and subtropics. Estimates of burden are uncertain, because many cases are not diagnosed or reported, and the numbers differ among sources.

• Malaria. The WHO estimated about 250 million cases and about 600,000 deaths in 2022 and 2023, in about 85 countries, with roughly 95 percent of deaths in the WHO African Region and about three quarters of deaths in children under 5 years. Many countries have eliminated malaria, and the WHO has certified a number of them in recent years.
• Dengue. Modeling estimates about 390 million infections a year, about 96 million of which are symptomatic. Reported cases rose from about half a million in 2000 to more than 5 million in 2019, more than 6 million in 2023, and more than 13 million in 2024, with expansion to new regions, including parts of southern Europe, the southern United States, and highland areas. Part of the increase is due to better reporting.
• Yellow fever. Modeling for 2013 estimated 84,000 to 170,000 severe cases and 29,000 to 60,000 deaths a year, mostly in Africa, despite the availability of a vaccine.
• Lymphatic filariasis. Tens of millions of people are infected, and about 600 to 900 million live in areas that need preventive treatment. Mass drug administration has reduced the burden, and some countries have eliminated it as a public health problem.
• Japanese encephalitis. Tens of thousands of clinical cases occur a year in Asia, with a case fatality of about 20 to 30 percent and neurological sequelae in many survivors.
• Chikungunya and Zika. Large epidemics occurred in the Americas in 2013 to 2017 (Zika in 2015 to 2017), and chikungunya has caused outbreaks in the Indian Ocean region and in Asia, with local transmission in Europe.

Emerging and spreading threats

Several ecological and evolutionary trends are altering the global distribution of mosquito-borne disease:

• Invasive vectors. Aedes albopictus has spread to every inhabited continent. Anopheles stephensi, an urban malaria vector from South Asia, was detected in Djibouti in 2012 and later in Ethiopia, Sudan, Somalia, Nigeria, and Kenya, and it threatens malaria control in African cities.
• West Nile virus reached the United States in 1999 and spread to the whole country within a few years. It is now the main cause of arboviral disease there. Outbreaks occur in southern and central Europe each summer.
• Local transmission in temperate regions. Dengue, chikungunya, and in a few cases Zika have been transmitted locally in southern Europe by Aedes albopictus, after the introduction of the virus by infected travelers. The number of local cases has been increasing since 2022.
• Drug and insecticide resistance. Partial resistance of P. falciparum to artemisinin has emerged in the Greater Mekong region, and in Africa (Rwanda, Uganda, Eritrea, and Tanzania), and resistance of mosquitoes to pyrethroids is widespread.

Temperature

In mosquito-borne disease systems, mosquito and pathogen traits (development rate, survival, biting rate, and EIP) respond nonlinearly to temperature. Models fitted to laboratory data give a unimodal relationship of transmission suitability to temperature. The estimated optimum for Anopheles with P. falciparum is about 25 °C, with a range from about 17 °C to about 34 °C. For Aedes aegypti with dengue it is about 29 °C, with a range from about 18 °C to about 35 °C, and for Aedes albopictus with dengue it is about 26 °C. These estimates have wide uncertainty, and they were derived from laboratory data, so that they should be applied to field conditions with care. The EIP falls rapidly as the temperature rises, and so a warmer climate can allow transmission in places that were too cool, such as highlands and temperate regions, while transmission may fall in regions that become too hot, though mosquitoes can find cooler microhabitats.

Water, rainfall, and land use

Mosquitoes that transmit mosquito-borne disease need standing water to breed, so that rainfall, irrigation, and water storage affect their numbers. Heavy rainfall can create breeding sites for Culex and floodwater Aedes, and drought can increase the use of water storage containers that support Aedes aegypti. Irrigation and rice fields increase malaria vectors and Japanese encephalitis vectors, and deforestation can alter the abundance of forest malaria vectors such as Anopheles darlingi. Unplanned urban growth with poor water supply, drainage, and waste management is a main driver of the growth of dengue. The relation between climate and disease is also affected by human factors such as housing, access to health care, vaccination, and the movement of people, so that climate change is one of several drivers, and its importance differs among diseases and regions.

Climate oscillations

Interannual climate variability, such as the El Niño-Southern Oscillation, is associated with outbreaks of several mosquito-borne diseases through changes of temperature and rainfall, for example Rift Valley fever in East Africa, dengue in Southeast Asia and the Americas, and malaria in some highland regions. The associations are regional and differ among events.

Early understanding

Mosquito-borne diseases have affected humans for a very long time. Malaria parasites are found in ancient DNA, and fevers described in early texts are likely to include malaria. The name "malaria" comes from the Italian for "bad air", reflecting the belief that it was caused by miasmas of marshes. Patrick Manson showed in 1877 to 1878 that the filarial worm that causes elephantiasis develops in Culex mosquitoes, which was the first demonstration that an insect can transmit a human parasite. In 1880, Alphonse Laveran observed malaria parasites in the blood. Ronald Ross showed in 1897 to 1898 that avian malaria is transmitted by mosquitoes and traced the development of the parasite in the mosquito, for which he received the Nobel Prize in 1902, and Giovanni Battista Grassi and colleagues showed that human malaria is transmitted by Anopheles. Carlos Finlay proposed in 1881 that yellow fever is transmitted by mosquitoes, and the Walter Reed commission demonstrated this in Cuba in 1900 to 1901, and showed that the agent is a filterable virus, which made yellow fever the first human virus to be identified.

Control campaigns

In the history of mosquito-borne disease control, William C. Gorgas controlled mosquitoes in Havana and the Panama Canal Zone in the early twentieth century by eliminating breeding sites and by screening, and this made the completion of the Panama Canal possible. The insecticidal properties of DDT were discovered by Paul Müller in 1939, and its use for indoor residual spraying, with the drug chloroquine, supported the Global Malaria Eradication Programme launched by the WHO in 1955, which eliminated malaria from many countries in Europe, North America, and parts of Asia and Latin America but did not succeed globally, because of resistance, operational problems, and lack of funding, and it was abandoned as a global goal in 1969. Fred Soper led campaigns against Aedes aegypti in the Americas from the 1930s to the 1960s, which eliminated it from most countries, but it returned when the programs lapsed. The development of dengue, chikungunya, and Zika as global problems is mainly the result of the spread of Aedes aegypti and Ae. albopictus with urbanization and trade. From the 1990s, insecticide-treated nets, artemisinin-based combination therapy, and rapid diagnostic tests, with funding from the Global Fund and the President's Malaria Initiative, led to a large decline of malaria deaths between 2000 and 2015. Progress then slowed.

The clinical features of mosquito-borne diseases differ among pathogens. Many arbovirus infections are mild or without symptoms, and common features are fever, headache, muscle and joint pain, and rash. Severe forms include hemorrhage and shock (dengue, yellow fever), encephalitis (Japanese encephalitis, West Nile virus, equine encephalitides, La Crosse virus), liver failure (yellow fever), chronic arthritis (chikungunya, Ross River virus), and congenital defects (Zika). Malaria causes fever and chills that recur, anemia, and, in severe P. falciparum infection, cerebral malaria, respiratory distress, and kidney failure, and it is a medical emergency. Lymphatic filariasis causes chronic lymphedema and hydrocele. Diagnosis uses microscopy and rapid antigen tests (malaria), RT-PCR and antigen detection in the first days of illness, and serology later, which often cross-reacts among related flaviviruses and so may need confirmation by neutralization tests. Treatment of most arboviral diseases is supportive, since there are no licensed antiviral drugs for them. Malaria is treated with antimalarial drugs, in particular artemisinin-based combination therapy for P. falciparum, and, for P. vivax and P. ovale, with a drug that clears the dormant liver stage (primaquine or tafenoquine, with a test for glucose-6-phosphate dehydrogenase deficiency).

Vector control

Vector control reduces the contact between people and infected mosquitoes, and it is the main preventive measure for mosquito-borne diseases that have no vaccine. The methods include:

• Insecticide-treated nets and long-lasting insecticidal nets, the most widely used method against malaria in Africa. They reduced child mortality by about 17 percent in trials, and resistance of mosquitoes to pyrethroids has led to nets with a synergist (piperonyl butoxide) or a second insecticide.
• Indoor residual spraying of long-acting insecticides on walls, for malaria vectors that rest indoors.
• Source reduction and larval control by removing or covering containers, draining and managing water, and treating water with larvicides (such as Bacillus thuringiensis israelensis and insect growth regulators), which is the basis of control of Aedes aegypti and depends on community participation. Space spraying has a short effect and is used mainly during epidemics.
• Personal protection: repellents (DEET, picaridin, and others), screens, and clothing.
• New approaches: release of Aedes aegypti carrying Wolbachia, which reduced symptomatic dengue by 77 percent in a randomized trial in Yogyakarta, Indonesia, release of sterile or incompatible males, genetically modified mosquitoes, spatial repellents, attractive toxic sugar baits, and gene drives, which are being developed for Anopheles but have not been released in the field.

The details of the methods, of integrated vector management, and of insecticide resistance are described in the article on vector control.

Vaccines and drugs

Vaccines and preventive drugs

Surveillance and early warning

Surveillance of mosquito-borne disease combines notification of human cases, laboratory confirmation, testing of mosquitoes for pathogens, monitoring of vector density (with ovitraps, adult traps, and larval surveys), surveillance of animal hosts (such as dead birds for West Nile virus and sentinel chickens, and dead monkeys for yellow fever), and monitoring of insecticide resistance. Forecasting models use climate, vector, and human data to anticipate outbreaks, and satellite imagery and citizen science platforms are used to map breeding sites and to detect invasive species. The International Health Regulations require countries to report certain events, and travelers to some countries must show proof of yellow fever vaccination.

Global efforts to control mosquito-borne diseases confront several persistent challenges:

• Insecticide and drug resistance, including the resistance of malaria parasites to artemisinin and of mosquitoes to pyrethroids.
• Behavioral changes of vectors, such as the shift of some Anopheles to biting outdoors and in the early evening after the use of nets, which reduces the effect of indoor methods.
• Urbanization and trade, which provide breeding sites and move vectors and pathogens.
• Climate change, which alters the range and season of transmission, with effects that differ among diseases and regions.
• Funding and health systems. Gains can reverse when programs are interrupted, as in the resurgence of malaria after the end of the eradication campaign, and conflict and displacement reduce coverage.
• Co-circulating viruses. Dengue, Zika, chikungunya, and yellow fever share vectors and cross-react in serological tests, which complicates diagnosis and surveillance.

Why do only female mosquitoes transmit mosquito-borne diseases?

Male and female mosquitoes both feed on plant nectar and honeydew to obtain carbohydrates for flight metabolism, but only adult females possess piercing-sucking mouthparts (mandibles and lacinias) capable of penetrating vertebrate skin and cannulating capillaries. Females require vertebrate blood meals (anautogeny) to acquire protein, iron, and lipids that trigger target-of-rapamycin (TOR) and 20-hydroxyecdysone signaling in the fat body to synthesize yolk vitellogenin for egg maturation.

What is the difference between anthroponotic and zoonotic mosquito-borne transmission cycles?

In anthroponotic mosquito-borne cycles—such as *Plasmodium falciparum* malaria and urban dengue—humans serve as the primary amplifying reservoir host, meaning the pathogen can be eliminated locally by interrupting human-mosquito contact or clearing human parasitemia. In zoonotic cycles—such as West Nile virus and Japanese encephalitis—wild birds or pigs act as the amplifying reservoirs while humans typically develop low-titer viremia as dead-end hosts, requiring veterinary or human vaccination and vector suppression rather than human case treatment to halt transmission.

How does the extrinsic incubation period constrain pathogen transmission in wild mosquitoes?

The extrinsic incubation period (EIP, n) is the temperature-dependent interval between a mosquito ingesting an infectious blood meal and the pathogen traversing the midgut and hemocoel to render the salivary glands infectious. Because wild female mosquitoes suffer high daily mortality (μ ≈ 0.10–0.15 per day), the fraction surviving the EIP decays exponentially as e^−_μn_, meaning that cool temperatures that lengthen n beyond the typical adult lifespan halt transmission.

• Vector control
• Arbovirus
• Malaria
• Dengue fever
• Yellow fever
• Zika fever
• West Nile fever
• Aedes aegypti
• Aedes albopictus
• Wolbachia
• Vector-borne disease