Zoology

Mosquitoe Diseases



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Mosquito is the name of a blood-sucking fly, a member of the insect family Culicidae and the order Diptera (true flies) and it is distinguished from most other flies by the comparatively long proboscis which projects from the head, a very slender body, and narrow scale-bearing wings. The mosquito's proboscis is actually the equivalent of the labium, i.e. the lower lip in other insects, modified into a grooved projection that allows the insect's other mouth parts to slide into it. The mouth parts also consist of very fine stylets which constitutes the insects piercing equipment.

Male mosquitoes live on the juices of plants and flowers and, consequently, their stylets are much smaller than those of the female insects which live on a combination of plant/flower juices and animal blood; the longer and stronger stylets of the female being required so as to be able to pierce through the skin of the animal from which the mosquito is feeding. When the female is about to take a blood meal, about once a week on average, she settles ever so lightly on its victim that, oftentimes, her presence is unnoticed. The puncture is made by two pairs of stylets (corresponding to the mandibles and maxillae, organs corresponding to the lower and upper jawbones in higher animals, of other insects). Two, unpaired, stylets are used to suck blood from the victim (the upper unpaired stylet) and to inject saliva into the victim (the lower unpaired stylet). It is this injection of saliva into the victim's bloodstream that makes the mosquito a very formidable adversary to many animal species, for it is through the saliva that the parasitic microorganisms that cause diseases are passed to the victim.

Mosquitoes are found in every part of the world, and there are more than 1,500 species of the insect worldwide. Most of these species inhabit the tropical and sub-tropical regions of the world, but, even in the Arctic, there are species of this ubiquitous insect, alive and well.

Mosquitoes can be divided into two broad groups, the Anophelini and the Culicini. The main difference between the species which constitute the two groups is that amongst the anophelines, the palpi (the sense organs attached to an insect's mouth parts) of the female are roughly the same length as the proboscis, and, when at rest, the insect's body is aligned at an angle to the supporting surface. The culicines, on the other hand, have palpi that are considerably shorter than the proboscis, about a fifth the size of the proboscis on average, and, when at rest, the insect's body lies more or less parallel to the supporting surface.

Mosquitoes, at least certain species of the insect, play a very important role in matters of human welfare. The anopheles genus, for instance, is the vector, i.e. the carrier of a disease, of the protozoan parasite, plasmodium, which parasite causes malaria, which is the world's most common disease (affecting up to 500 million people worldwide every year) as well as being the world's greatest killer disease (causing the death of up to 3 million people per annum, most of them children in sub-Sahara Africa).

But, although malaria is the most devastating aspect of man's relation with mosquitoes, it is by no means the only one. The tiger mosquito, culex fatigans, is the vector of the filarial worm which causes elephantiasis, a mainly tropical disease, which causes an excessive growth of skin and connective tissue especially on the legs and scrotum. Mosquitoes again, this time the aedes aegypti genus, are also responsible for yellow fever a viral tropical disease characterized by high fever jaundice, acute nephritis, hemorrhages and a high mortality rate. In addition, this genus is the vector for dengue fever, which affects an estimated 40 million people a year and dengue hemorrhagic fever which affects hundreds of thousands.

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