Malaria is caused by a protozoan Plasmodium. The infective stage of the parasite is transmitted through the bite of the female Anopheles mosquito along with its saliva. The incubation period is about three weeks. The parasite grows and multiplies in the red blood cells and destroys them during the process. Chill and high fever are repeated on the third or fourth day. When the mosquito bites a patient, the parasite is sucked in along with the blood. It grows and multiplies within the mosquito. Various drugs such as quinine, paludrin, comoquin etc. are useful in treatment. The disease is common in hot and humid countries.
There are three kinds of mosquitoes commonly found. These are, the malaria disease causing mosquito Anopheles, the filaria mosquito Culex and the dengue mosquito Aedes. Although the life-history of all types of mosquitoes shows the same basic stages i.e . eggs larvae, pupae and adults. Minor differences instructure and behabaviour are found in these stages. The adults of Anopheles and Culex can be recognized in their sitting posture. Anopheles always rests with its straight body making an angle against the surface, while Culex keeps its body more or less parallel. The anopheles lays its eggs singly and horizontally. Each eggs have small air spaces on either side makeing them buoyant. The larva of anopheles floats parallel to the surface of water, secondly the respiratory tubes if anopheles are short.
Only female mosquitoes can suck blood. They have sharp pointed mouth-parts (proboscis) for puncturing the skin. The males have blunt and somewhat spread-out mouth parts by which they can suck only exposed fluids from drains or plant surface.
Anopheles spreads malaria in man, monkeys, birds etc. The malaria germ is a protozoan Plasmodium. Culex spreads elephantiasis, filariasis caused by a Wuchereria. A third mosquito Aedes spreads yellow fever and dengue both caused by their viruses. The germs of these diseases are spread when the mosquitoes bite to suck blood. With this blood, the mosquitoes receive germs of the particular disease, which grow and multiply within their body. When such infected mosquitoes bite a healthy person, these germs are introduced into the body through the saliva. Before sucking blood the mosquito first injects its saliva into the skin, which contains a substance that prevents clotting of blood to facilitate suction.
Mosquitoes breed in warm humid weather especially in the rainy season when enough ponds and puddles are available with stagnant water. Mosquitoes can breed in small quantities of water as in old discarded cans and vessels filled with rain water.
Several steps are recommended to destroy mosquitoes in different stages:
Spraying - Adult mosquitoes must be destroyed by spraying DDT and other insecticides in dwelling places. Spraying on ponds and marshy places kills the life-history stages.
Elimination of breeding places - Breeding places should be destroyed. Small ponds and puddles should be filled up.
Spraying on stagnant water - Kerosene or some other greasy oil should be poured over the water to make a thin film on the surface. The oil kills the larvae and pupae when they come to breathe on the surface.
Biological control - Certain fishes such as Gambusia should be introduced in the ponds. They selectively devour mosquito larvae.
Tips and comments
Control measures include destruction of the mosquito at all stages and to avoid mosquito bite use mosquito nets or repellants.
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