Mosquito-borne Diseases

Who has not been annoyed by the itch of a mosquito bite? Luckily, most bites are only a light nuisance. Yet, some mosquitoes may come with a disease-causing microbe.

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Mosquito-borne diseases cannot spread directly from person to person. A susceptible mosquito must first bite an infected person and acquire the microbe. When that mosquito later bites a susceptible person, the infection can be transmitted to that person, who may become sick with that microbe.

Malaria is such a disease. It is caused by a parasite with a remarkably complex life cycle. After entering the human body, the parasite first develops in liver cells and later infects red blood cells. Parts of its life cycle take place inside the mosquito, before it can spread to another person.

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Mosquito-borne diseases are strongly shaped by environmental and human factors. Immature mosquitoes (before they develop wings and fly) develop in water, meaning that the presence of water at some stage is an absolute requirement for mosquito reproduction. Different mosquito species tend to have specific preferences for the type of water body they will lay eggs in, going from tree holes, muddy footprints, puddles to irrigated fields and man-made containers.

Mosquitoes are also sensitive to weather conditions, which may affect their activity and survival. Warmer temperatures, for example, accelerate the development of the malaria parasite inside the mosquito’s stomach, since mosquitoes cannot regulate their own body temperature. This explains why climate change has become a major focus in research on malaria transmission, as well as other mosquito-borne diseases, in the last two decades.

At the same time, human interventions strongly affect mosquito habitat and limit transmission. Drainage of wetlands, mosquito control, individual protection, or disease treatment can all reduce the spread of the disease. The vast changes that have been observed all over the world in the past century illustrate how environmental transformation and public health measures can reshape the geography of an infectious disease.

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Today, malaria-endemic regions are facing new challenges, including mosquitoes resistant to insecticides and parasites resistant to antimalarial drugs. In our region, mosquito-borne diseases may once again become an increasing concern through other mosquito species and other mosquito-borne diseases. The tiger mosquito (Aedes albopictus) is getting widely established across Europe and can transmit viruses such as dengue, Zika, chikungunya, which are frequently introduced by people travelling from areas where those viruses are widespread. Spotted a tiger mosquito? You can help scientists follow its spread by reporting it to Sciensano on their dedicated app (surveillancemoustique/muggen surveillance).