World Mosquito Day - 2017

Aug 18, 2017 |
Mosquito Larvae in a petri dish


August 20th is World Mosquito Day, which marks the historic discovery by British doctor Sir Ronald Ross in 1897 that female Anopheles mosquitoes transmit malaria between humans. This finding provided the foundation for scientists across the world to better understand the deadly role of mosquitoes in disease transmission and devise effective innovative interventions.

Mosquitoes 101

Vector-borne diseases or diseases carried by insects, ticks, and small animals have plagued humanity for millennia. The most common vectors include mosquitoes, sandflies, bugs, ticks, and snails, which are responsible for transmitting a wide range of parasites and pathogens, but mosquitoes are the deadliest. Mosquitoes kill nearly three-quarters of a million people each year worldwide and sicken millions more. Malaria by itself is responsible for more than half of mosquito-related deaths, predominantly in sub-Saharan Africa. Mosquitoes also transmit dengue, lymphatic filariasis, chikungunya, Japanese encephalitis, and yellow fever, among other diseases.

Of the 3,500 known species of mosquitoes, only those from three genera transmit diseases to humans:

  • Anopheles mosquitoes are the only species known to carry human malaria. They also transmit filariasis and encephalitis.
  • Culex mosquitoes carry encephalitis, filariasis, and the West Nile virus.
  • Aedes mosquitoes, of which the voracious Asian tiger is a member, carry yellow fever, dengue, chikungunya, and Zika.

Only female mosquitoes bite as they need the amino acids from blood to develop and lay eggs. Male mosquitoes, on the other hand, use nectar as a source of energy. Transmission occurs when female mosquitoes bite an infected human and then transfer the pathogen to the next person they bite through their saliva.

Mosquito-borne Diseases

Malaria – Malaria is caused by a parasite that is transmitted by an Anopheles mosquito. Malaria is prevalent in tropical or sub-tropical climates. In 2015, about 3.2 billion people – almost half of the world's population – were at risk of malaria. Most malaria cases and deaths occur in sub-Saharan Africa, but people in Asia, Latin America, and, to a lesser extent, the Middle East are also at risk. Children are especially vulnerable. There were 214 million cases of malaria in 2015 worldwide, and 438,000 people died as a result of the disease.

Yellow Fever – Yellow fever no longer occurs in the United States or Europe, but it is prevalent in Africa and parts of South America. It is transmitted by the Aedes aegypti mosquito. Yellow fever produces symptoms similar to malaria but also includes nausea, vomiting, and jaundice. Like malaria, yellow fever can be fatal.

Encephalitis – Encephalitis is caused by viruses that are transmitted by mosquitoes – such as the Aedes or Culiseta mosquitoes. The symptoms of encephalitis include high fever, stiff neck, headache, confusion, and lethargy/sleepiness.

Dengue Fever – Dengue fever is transmitted by the Asian tiger mosquito (Aedes albopictus) and Aedes aegypti. While these mosquitoes are native to Asia and Africa, respectively, they have spread throughout the tropics. Dengue fever is caused by a virus that produces a range of illnesses from viral flu to hemorrhagic fever. It is especially dangerous for children.

Zika – Zika is a disease caused by the Zika virus, which is spread to people primarily through the bite of an infected Aedes species mosquito. The most common symptoms of Zika are fever, rash, joint pain, and conjunctivitis (red eyes). The illness is usually mild with symptoms lasting for several days to a week after being bitten by an infected mosquito. However, Zika virus infection during pregnancy can cause a serious birth defect called microcephaly, as well as other severe fetal brain defects. Once a person has been infected, he or she is likely to be protected from future infections. Zika can also lead to Guillain-Barré Syndrome in rare cases.

West Nile VirusDozens of species have been known to carry West Nile, but the Culex pipiens is the primary culprit. Most healthy people don’t even know they have been infected, but West Nile can cause flu-like symptoms and, in rare cases, permanent neurological damage or death.

Chikungunya – Chikungunya is a virus most often spread to people by Aedes aegypti and Aedes albopictus mosquitoes. These are the same mosquitoes that transmit dengue virus. The most common symptoms of chikungunya virus infection are fever and joint pain. Other symptoms may include headache, muscle pain, joint swelling, or rash.

Entomological Monitoring

The recent progress in malaria control has been largely accomplished through a massive increase in vector control from the use of insecticide-treated nets (ITNs) and indoor residual spraying (IRS). Since both of these prevention measures depend on the ability of insecticides to kill, repel, or reduce the lifespan of female mosquitoes, understanding and monitoring the composition of the vector population, mosquito behavior, and insecticide resistance status are critical to their continued effectiveness. Periodic collection of entomological data is essential to inform vector control strategies and track their impact on malaria transmission.

The President’s Malaria Initiative’s (PMI’s) investments have resulted in a substantial improvement in country capacity to implement entomological monitoring. All 19 PMI focus countries in Africa currently conduct regular entomological monitoring with PMI support. PMI supports a total of 190 insecticide resistance monitoring sites and approximately 130 entomological monitoring sites, which measure mosquito density, behavior, species mix, and sporozoite rates.

Learn more about PMI’s entomological monitoring work:

Photo credit: Brant Stewart, RTI

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