Malaria
disease

Biology
of mosquitoes as the vector for the malaria parasite

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They are two winged
flying insects that suck blood from humans and animals. Mosquitoes have a
slender body, long legs and long needle-shaped piercing mouthparts. The wings
of anopheles mosquitoes are spotted and the adults measure between 2mm to
12.5mm in length.

Life cycle of
mosquitoes

Mosquitoes have four
distinct stages in their lifecycle and they include egg, larva, pupa and the
adult mosquito. The females only bite once but they produce eggsbat intervals
throughout their life. In order to be able to produce the eggs the female
mosquitoes require a blood meal and the digestion and developments of eggs
takes2-3days. The females then search for suitable places to deposit their eggs
after which another blood meal is taken and another batch of eggs is laid. The
process is repeated until the mosquito dies. The female mosquitoes lay between
30 and 300 eggs at a time. The female anopheles mosquitoes lay their eggs
directly on the surface of water, singly and they contain floats. The larval
period lasts between 4 to 7 days after which the fully grown larva changes into
a comma-shaped pupa which does not feed and spends most of its time under the
water surface. When mature, the pupal skin splits at one end and a fully
developed adult mosquito emerges.

Species of malaria
parasite

Malaria is caused by
protozoan parasites of the genus plasmodium vectored by the female anopheles
mosquito. There are four species of malaria parasite which infect han beings
which are;

Plasmodium falciparum

This species causes
tropical malaria which occurs throughout tropical Africa, Kenya being one of
the tropical countries. It also occurs in parts of Asia, Western Pacific, South
and Central America.

Plasmodium vivax

It causes tertian
malaria which causes fever after every second day. The species is found in Asia
and Central America but almost absent in Africa.

Plasmodium malariae

Causes tertian malaria.
This is a type of malaria which causes fever that recurs after every four days.
It is found worldwide but has a very patchy distribution.

Plasmodium ovale

This plasmodium species
causes tertian malaria. It occurs mainly in tropical West Africa and rarely in
the western pacific.

Malaria is among the
leading causesnof death in Kenya especially in children and pregnant women.
Treatment of malaria is complicated by the spread of strains of plasmodium
falciparum resistance to the commonly used antimalarial drugs and the high cost
and toxicity of the alternative drugs.

Transmission of malaria

Malaria parasites enter
the human body via the bite of a malaria-carrying anopheles mosquito. The
parasites invade the liver through the blood stream and multiply. During this
period the victim doesn’t feel sick. After nine days, the parasites invade the
blood stream and invade the red blood cells. At this stage the parasites are
referred to as merozoites and they continue to multiply. A few days after the
appearance of the first symptoms some merozoites develop into gametocytes which
is the sexual stage in the lifecycle and continues to circulate in blood. The
gametocytes are picked by female anopheles mosquitoes during blood-feeding.

Malaria prevention

Prevention is aimed at
avoiding bites of the anopheles mosquito. This can be done through different methods
which include the following;

Wearing of protective
clothing

Use of repellents on
exposed skin, mosquito coils and other insecticides.

Sleeping under mosquito
nets which are treated with insecticide

Use of prophylactic
drugs by visitors to malaria endemic areas to prevent the development of the
disease. These drugs may also be used by children under five years and pregnant
women in areas of endemicity.