Parasitic Protozoa

The protozoa are single-celled organisms whose structure is more similar to the cells of animals than to bacteria. There are many parasitic protozoa of animals, although only relatively few types infect humans.

Malaria

Malaria is caused by parasitic protozoa called plasmodia. There are several types of malaria infecting a wide range of animals, but the two most important human infections are Plasmodium vivax and Plasmodium falciparum.

The malarial parasite has a complex life-cycle involving both mosquitoes and humans. The plasmodium multiplies in the red blood cells and liver cells of humans, finally producing the sexual stages: male and female gametes. For these to develop further, a female anopheles mosquito must bite the infected person and take up the sexual stages in the blood it feeds on. In the gut of the mosquito, the male and female stages join and, after several stages of multi­plication, produce many more infective stages. These reach the salivary gland, of the insect and are injected into the blood of another human when the mosquito feeds again.

Malaria is widespread in many tropical and subtropical countries where the anopheles mosquito lives. It is the world's single greatest cause of death and disablement. Mosquitoes breed in still, stagnant water and one of the ways in which the disease is fought is to drain swampy areas, or to spray them with insecticides. Since the mosquitoes feed at night, sleeping under an excluding fine net can prevent them biting an individual.

Symptoms

The symptoms of malaria are a result of the damage caused by the multiplication of the various stages in the blood and liver cells. The diagnosis is made by microscopic examination of the blood for parasites. There is a chill with severe shivering, backache, headache and a dry cough. The skin is pale and the pulse rapid. After an hour the temperature begins to rise to as high as 41°C (106°F) with sweating, restlessness and dehydration followed by a fall in temperature. Blood cells are destroyed by the parasites, and this may cause anaemia. Damage to the liver may result in jaundice.

Treatment

Treatment of malaria consist, of a course of drugs which must be continued for several weeks, even though symptoms are usually relieved within a few hours. Several anti-malarial drugs, such as chloroquine and Paludrine, can prevent the infection developing; these must be taken continually in a malarial region, and for a month afterwards.

Prevention

There are two important measures to prevent malaria infection: avoiding mosquito bites and using antimalaria medication.