The outbreak in Machakos District; epidemiological features and a possible way of control

Abstract

The epidemiology of kala-azar was studied in East Katangini, the area in Machakos District where the incidence of the disease had been highest during the epidemic years 1977–1979.

A house-to-house survey showed that 19·3% of the homesteads had harboured kala-azar patients in the period 1977–1980, while 3·2% of the people had suffered from the disease.

Significantly more males had had the disease than females and more children than adults, while the male patients came mainly from poorer homesteads.

Significantly more kala-azar occurred in homesteads within 200 metres of a termite hill, while kala-azar seemed to occur particularly in homesteads near dry river beds.

During a period of one year, sandflies were caught in a small focus of infection. They were still common in rock fissures, but were rare in other resting sites such as termite hills and huts. Particularly, the man-biting Phlebotomus martini was rare, as were other man-biting insects such as Anopheles gambiae.

Very recently the farmers had begun to grow cotton which was sprayed regularly with insecticides stored mostly in the farmers' homes. As a result, the number of new patients in 1980 fell to four, and the longer the people had stored insecticides in their compounds, the lower was the recent kala-azar incidence in these homesteads.

Presumably the insecticide treatments killed many sandflies and other insects, while the storing of insecticides protected the people inside their huts, although some patients probably became infected outside, probably near termite hills.

It is suggested that the growing of cotton as a cash crop may be a good control method for kala-azar in the dry areas in Eastern Kenya, unless this would lead to insecticide pollution of the water supply.