Biology

Deadly mosquitoes

There are animals that are dangerous to humans. When reading this sentence, we can think of predators such as sharks , lions or wolves. Poisonous animals, such as snakes or scorpions, can also come to mind. Some animals that cause numerous deaths every year are crocodiles and alligators, hippos or dogs (which transmit rabies).

The  Homo sapiens  has a respectable second place in the list of most dangerous animals to man. But the animal that causes the most deaths, with about a million victims each year, is the mosquito . In this article we will explain which are the life threatening diseases transmitted by mosquitoes and which species are the most dangerous.

Some nasty bugs

Deadly mosquitoes
Deadly mosquitoes

Adult mosquitoes, male and female, generally feed on fruit or plant juices. However, the females of some species of mosquito also feed on the blood of different species of animals.

This supply of nutrients allows them to lay eggs, which develop as larvae in aquatic environments. Stagnant water is an ideal environment for mosquitoes to breed. There are several species that lay their eggs exclusively in the accumulations of water that form on some plants.

Not all mosquito species require a blood supply to lay eggs (such as those of the genus  Toxorhynchites ), and some species (mainly of the genus  Culex ) only require a blood meal after having made the first lay.

 

Not all species of mosquitoes feed on human blood, and those that do not all carry disease. Some 3,500 different species of mosquitoes have been described, divided into 112 genera. Of these, those that group the largest number of disease-transmitting species are three:  Culex  (a genus comprising about 1,000 species),  Aedes  (700 species) and  Anopheles  (200 species). Within each genus there are several species that can transmit the same diseases. Notably, the only mosquitoes that can transmit malaria belong to the genus  Anopheles . The word  Aedes  comes from the Greek aēdēs (ἀηδής), which means “unpleasant.”

Mosquito-associated diseases

Mosquito bites are quite annoying, but they do not pose a health risk by themselves. The problem is the infectious agents that mosquitoes spread with their bites, similar to what happens with some ticks .

Female mosquitoes have specialized mouthparts to pierce the skin, and their saliva contains anticoagulant substances that facilitate blood flow. These substances are what cause the characteristic swelling in the area of ​​the bite. On the other hand, it is through the saliva of mosquitoes that the transmission of pathogens occurs.

Dengue

One of the best known mosquito-borne diseases is dengue, caused by the dengue virus, which is spread by mosquitoes of the genus  Aedes , especially  Aedes aegypti . The disease is present in all the continents of the southern hemisphere and each year some 390 million people are infected, resulting in 40,000 deaths. A vaccine has recently been developed, but it is not recommended for use in the general population due to certain contraindications if the person has not yet suffered from the disease.

Malaria or malaria

Another mosquito-borne disease is malaria or malaria (from the Latin  paludis , meaning swamp or swamp). This disease is caused by a parasite, being caused by different species of protists of the genus  Plasmodium . Mosquitoes of the genus Anopheles are responsible for transmitting this disease, which infects more than 200 million people each year and causes about 400,000 deaths.

There is only one vaccine, recently approved for use. Malaria can be completely cured if it is treated in time effectively with antimalarial drugs, or else it can remain latent in the patient’s body for decades.

Yellow fever

Yellow fever or black vomit is a viral disease transmitted by mosquitoes of the Aedes  or  Haemagogus genera  . The names of the disease come from its symptoms, the yellow color of jaundice (yellowing of the skin) and vomiting of clotted blood.

An estimated 200,000 people are infected each year and about 30,000 die. The acute form of the disease has a mortality rate of 50%. Malaria is present throughout the southern hemisphere and some countries in the northern hemisphere. There is an effective vaccine that fully immunizes with a single dose, but there are no known medications to cure the disease once contracted. The use of aspirin in patients with malaria is dangerous, due to its anticoagulant effects, which can cause internal bleeding.

Other diseases caused by mosquitoes

Other diseases transmitted by mosquitoes but which are less widespread are lymphatic filariasis (also called elephantiasis caused by a nematode, transmitted by the genera  Aedes ,  Anopheles ,  Culex  and  Phlebotomidae ), chikungunya ( Aedes ), Rift valley fever ( Aedes ), Zika virus ( Aedes ), Japanese encephalitis ( Culex ) or West Nile fever ( Culex ). 

The annoying traveling mosquito

One species of mosquito that has gained some notoriety in recent years is the tiger mosquito ( Aedes albopictus ), native to Southeast Asia and introduced to many countries in Europe, the US, Brazil and equatorial areas of Africa.

It is an invasive species , whose eggs resist desiccation and can be transported in various ways. One route of entry for the mosquito into Europe was the transport of tires that contained stagnant water inside and mosquito larvae. 

This mosquito differs from others in that its period of activity is diurnal, and its oral apparatus is so developed that it is capable of biting through clothing (which the writer of these lines can confirm from his own experience). However, its bite is no more annoying than that of the common European mosquito ( Culex pipiens ).

This species is a transmitter of dengue, yellow fever, chikungunya and West Nile fever. For this reason, its introduction in new geographical areas is very problematic.

It has been present in Spain since 2004, but no epidemic outbreaks associated with this mosquito have been detected in our country. In 2005 it caused an epidemic of chikungunya on the French island of Reunion, while in 2007 there was another outbreak of this disease in Ravenna, Italy.

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