Mosquitos are flying insects which resemble crane flies and chironomid flies. They go through four stages in their life: egg, larva, pupa and adult (imago). Adult females lay eggs in stagnant water, for example reservoirs or in containers such as plastic buckets or paddling pools.
Male mosquitoes generally feed on nectar and plant juices, whereas the females often feed on blood, including the blood of humans. This is because they need the nutrition from the blood before they can lay eggs. Mosquitoes feed from their mouth-parts which are adapted to pierce the skin and then “suck” the blood. Prior and during blood feeding, the females inject saliva into the bodies of the blood source. This serves as an anticoagulant, meaning that it prevents the host blood from clotting.
Mosquitoes can carry and transmit diseases such as malaria, yellow fever, dengue fever, Chikungunya and West Nile. At least two million people a year die from these diseases.
Malaria is a mosquito-borne infectious disease of humans caused by eukaryotic protists of the genus Plasmodium. It is widespread in tropical and subtropical regions, including much of Sub-Saharan Africa, Asia and the Americas. The disease results from the multiplication of malaria parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases progressing to coma, and death. When properly treated, a patient with malaria can expect a complete recovery.
Yellow fever is an acute viral haemorrhagic disease. The yellow fever virus is transmitted by the bite of female mosquitoes and is found in tropical and subtropical areas in South America and Africa, but not in Asia. Yellow fever presents in most cases with fever, nausea, and pain and it generally subsides after several days. In some patients, a toxic phase follows, in which liver damage with jaundice (giving the name of the disease) can occur and lead to death. A safe and effective vaccine against yellow fever has existed since the middle of the 20th century and some countries require vaccinations for travellers. For yellow fever there is, like for all diseases caused by Flaviviruses, no causative cure.
Dengue fever, also known as breakbone fever, is an infectious tropical disease caused by the dengue virus. Typical symptoms include fever, headache, skin rash, and muscle and joint pains; in a small proportion the disease progresses to life-threatening complications such as dengue hemorrhagic fever (which may lead to severe bleeding) and dengue shock syndrome (where inadequate perfusion of tissues can cause organ dysfunction or failure and even death). There is currently no available vaccine, but measures to reduce the habitat and the number of mosquitoes, and limiting exposure to bites, are used to decrease the incidence of dengue. Treatment of acute dengue is supportive, using either oral or intravenous rehydration for mild or moderate disease, and intravenous fluids and blood transfusion for more severe cases. The incidence of dengue fever has increased dramatically over the last 50 years, with around 50-100 million people being infected yearly.
Chikungunya virus (CHIKV) is an insect-borne virus that is transmitted to humans by virus-carrying Aedes mosquitoes. There have been recent breakouts of CHIKV associated with severe illness. CHIKV causes an illness with symptoms similar to dengue fever. CHIKV manifests itself with an acute febrile phase of the illness lasting only two to five days, followed by a prolonged arthralgic disease that affects the joints of the extremities. The pain associated with CHIKV infection of the joints persists for weeks or months, or in some cases years. There are no specific treatments for Chikungunya. There is no vaccine currently available.
West Nile virus is a virus of the family Flaviviridae. Approximately 90% of West Nile Virus infections in humans are without any symptoms. It can be passed from human to human through blood transfusions, organ transplants and breast feeding. There is no vaccine for humans. West Nile virus has three different outcomes in humans. This first is an asymptomatic infection, meaning that the carrier experiences no symptoms. The second is a mild febrile syndrome termed West Nile Fever which has an incubation period of 2 to 8 days followed by fever, headache, chills, diaphoresis (excessive sweating), weakness, lymphadenopathy (swollen lymph nodes), drowsiness, pain in the joints and symptoms like those of influenza or the flu. The third is a neuroinvasive disease called West Nile meningitis which is characterized by similar early symptoms but also a decreased level of consciousness, sometimes approaching near-coma.