ntamoeba histolytica is one of a number
f species of small amoebae which live in the
alimentary canal of humans. These are usually
harmless protozoa, feeding on bacteria and
articles in the intestine. In certain conditions,
entamoeba invades the wall of the intestine or
rectum causing ulceration and bleeding, with
pain, vomiting and diarrhoea, symptoms of
moebic dysentery. The faeces of infected
eople contain resistant forms (cysts) of
ntamoeba. Conditions of poor sanitation and
hygiene, therefore, favour the spread of the disease.
Trypanosomes are flagellate protozoa which live in the blood stream. There are several different species of trypanosome and they cause diseases such as sleeping sickness, leishmaniasis and Chaga's disease and, in cattle, nagana. The sleeping sickness and nagana parasites are transmitted by the bite of the tsetse fly. This insect has tubular mouthparts, like the mosquito, and these pierce the skin to suck blood from a capillary. If the tetse fly bites an infected person, it sucks up the trypanosomes with the blood. The trypanosomes multiply in the body of the tsetse fly and invade the salivary glands. When the fly bites a healthy person, it injects saliva, which contains the trypanosomes.
The prevalence of tsetse flies in some areas makes it impossible to raise cattle because of the high incidence of nagana.
The main methods of control involve attempts to reduce the population of tsetse flies. This is done by using insecticides or by changing or removing the vegetation from the areas where the tsetse flies breed. These methods are only partially successful; spraying from the air, for example, is ineffective if the flies are resting on the underside of leaves.
new flagellum forming
Trypanosomes in the blood
by binary fission
© D.G. Mackean