In February 2022, Australian officials notified the public that Japanese encephalitis virus (JEV) had been detected in surveillance samples from several commercial pig farms. Residents were informed that JEV could be transmitted from pigs to humans by mosquitoes and were advised to avoid mosquito bites. As of April 20, 2022, 37 cases of JEV have been reported in Australia and three people have died.

While mosquitoes are most often thought of as a nuisance, they are actually among the world’s deadliest creatures. Mosquitoes contribute to about one million human deaths per year because they carry and transmit a variety of pathogens causing diseases including malaria, dengue, West Nile, yellow fever and Zika. The geographic distribution of these diseases varies by the regions inhabited by their mosquito vectors. For example, the parasites that cause malaria are transmitted by the Anopheles mosquito, which lives in tropic and subtropic regions. Therefore, malaria is prevalent in tropical areas of the world and rare-to-nonexistent in temperate, continental, and polar climates.

The discovery of mosquitoes as a vector for disease is a fascinating chapter in medical history. While lymphatic filariasis may have been the first infectious disease linked to mosquitoes (in 1877) due to the ability to easily visualize the parasites, the story of yellow fever virus is one of tragedy.

In 1881, Cuban physician Dr. Carlos Finlay hypothesized that yellow fever virus was spread by an intermediary host and proposed mosquitoes as the culprit. First, Finlay had observed a peculiar pattern of spread of yellow fever among individuals without direct contact with each other even while sparing spread among some with considerable exposure. Finlay also noticed that yellow fever epidemics correlated with weather patterns associated with mosquito activity. For his contribution, Dr. Finlay was dubbed “The Mosquito Man” and a quack by the medical community at the time.

While mosquitoes are most often thought of as a nuisance, they are actually among the world’s deadliest creatures.

In 1900, U.S. Army Major and physician Walter Reed was tasked with leading the Havana Yellow Fever commission to study transmission of yellow fever in Cuba. His team included Army surgeon Jesse Lazear, who had followed Finlay’s work on mosquitoes. In order to prove that mosquitoes transmitted the disease, Lazear brought lab-bred mosquitoes to hospital wards full of yellow fever patients. Holding jars of mosquitoes upside down on the skin of patients, the mosquitoes had full reign to take a blood meal. Lazear then let those same mosquitoes bite healthy soldiers, himself included. When the soldiers started showing signs of yellow fever, it was clear that mosquitoes could transmit the disease. Lazear’s self-experiment also proved deadly when he himself died of yellow fever during his experiment at the age of thirty-four.

Understanding transmission of communicable diseases is a central facet of public health to inform prevention strategies. For their work in Cuba, the Havana Yellow Fever Commission contributed to the start of mosquito eradication efforts in Central America that not only reduced incidence of yellow fever (and other mosquito-borne diseases) but is also proposed to have been critical to finishing the Panama Canal.

Vector/mosquito control is a central prevention strategy for all mosquito-borne diseases. Strategies range from regional interventions such as introduction of disease-resistant mosquitoes and large-scale chemical spraying, to individual methods such as use of screens and netting, insecticide repellents, and staying indoors during peak feeding times.

Additionally, several vaccines and prophylactic medications directed against mosquito-borne diseases are available and are required or recommended for travelers to certain endemic areas.

For more information on mosquito control, see the topic Mosquito Avoidance in DynaMed.