Approaches used to control trypanosomiasis include, parasite control, vector control and the exploitation of trypanotolerant livestock breeds.
The most commonly used method for control of trypanosomiasis in sub Saharan Africa is based on trypanocidal drugs (chemotherapy). Livestock survive in tsetse infested areas of africa due to extensive use of trypanocidal drugs. Chemotherapy is effective when drugs are properly used to provide cost effective and sustainable approach to Trypanosomiasis control. Trypanocidals can be highly effective provided they are continuously available and treatments are given regularly at appropriate dose rates; but they are often abused by farmers resulting in resistance.
Chemotherapy of trypanosomiasis in domestic animals is at present dependent upon a small number of compounds, namely: homidium, isometamidium, diminazene, quinapyramine and cymelarsan. Most of these compounds have been on the market for about 50 years now and there are reports of drug resistance in many parts of Africa, including Kenya. Furthermore, because of the close chemical relationships between the compounds, the development of resistance to one compound often appears to be associated with cross resistance to others.
There are several tsetse control/ eradication methods: aerial spraying, ground spraying, traps and insecticide impregnated targets, insecticide treated cattle and the Sterile Insect Technique (SIT). Aerial spraying using residual insecticide formulations have been applied from aircraft to control/ eradicate tsetse flies. Sequential Aerial Technique (SAT) spraying has been used to treat 10,000km2 in Botswana and 48,000 Km2 in Zimbabwe. The method has been used in Kenya, Nigeria, Somalia, Uganda, and Zambia with varying successes. SAT is used to treat large areas rapidly and is particularly appropriate in protected areas and epidemic situations. It is suitable where ground access is difficult, dangerous or inaccessible. However, SAT using Ultra-Low Volume (ULV) and non-persistent insecticide is expensive and cannot be implemented in areas with environmental concerns and ragged topography.
Targets and Traps
Target and trap techniques are intended to reduce populations of tsetse fly to levels which reduce the challenge or risks to humans and animals. They are also deployed to prevent re-invasion of the fly from a previously cleared area. Despite successful field trials, livestock farmers in Africa have been slow to adopt traps and targets as a means of tsetse control. Their motivation diminishes after the tsetse fly population is low as to pose threat to livestock health and therefore community based fly suppression efforts have been difficult to sustain.
Insecticide Treated Livestock
Insecticide treated cattle offer numerous advantages over odour-baited traps and targets. Cattle are used as moving targets and hence no cost for making artificial baits and reduced use of human labour. The cattle can move to all possible tsetse breeding and resting sites therefore are more efficient in tsetse control. The method can be based on existing infrastructure like dips and spray races which can bring about significant savings in operational costs. Other techniques can be integrated to address areas like hills not reachable by animal targets.
Sterile Insect Technique (SIT)
In SIT, male tsetse flies which have been rendered sterile by gamma irradiation are released into the field where they mate wild females, resulting in nonviable offspring. Once mated, there is no opportunity for the females to be mated by the fertile males as females mate only once in a lifetime. With the continuous release of sterile males in large numbers, it is possible to eradicate tsetse flies from a particular area. During the most recent campaign in Zanzibar, a ratio of more than 100 sterile males against one wild one was used to eradicate tsetse on the island. The method is very specific and does not pollute the environment. The effect on the population only becomes apparent after a period, as opposed to control by instantly killing insecticides.
Use of Trypanotolerant Livestock Breeds
It is well-known that innate resistance for many diseases, including trypanosomiasis, occurs in animal populations which have been subject to natural selection by exposure to disease pressure over many generations. In West Africa the N’dama and in Kenya the Orma Boran breeds possess trypanotolerant traits which can be exploited to improve livestock production in the tsetse infested areas. It should however be noted that these animals can act as disease carriers.