Tsetse control, agricultural expansion and environmental change in Nigeria
A brief account of the history of government organised tsetse and trypanosomiasis control in Nigeria is presented, and major features of the tsetse eradication programme are summarised. The achievements are considered in the context of widespread environmental change, brought about by an increasing human population, and a long term process of agricultural expansion, which have resulted in an overall reduction in natural tsetse habitats and hosts, and led to a general decline in tsetse populations. A comparison of two areas, one within, and the other outside the tsetse eradication zone, showed that they had both experienced similar rates of change in land use, and available information indicated that human and cattle populations had also increased at similar rates. The present day distribution and abundance of tsetse and cattle in a region of the Nigerian sub-humid zone, not yet reached by the tsetse eradication programme, are described. In the virtual absence of wildlife, abundance of cattle, and concentration of the two riverine tsetse species at crossing points, it was concluded that tsetse were largely dependent on cattle and/or man for their survival. The low density of riverine tsetse populations, their restricted distribution and their low infection rates, combined with Fulani herd management practices, which limited the period of contact between tsetse and cattle, indicated that under the prevailing conditions, trypanosome challenge was likely to be very low. It is suggested that this situation was typical for many areas within the sub-humid zone, and that in the future, similar conditions are likely to become even more widespread. It is concluded that, whilst government trypanosomiasis control programmes must have contributed to the general decline of the disease which has taken place, the environmental context within which they were mounted, has changed significantly. Over the past fifty years human population has almost certainly increased three or four fold, and the extent and intensity of both farming and hunting have increased commensurately. This has resulted in an overall reduction in natural tsetse habitats and hosts, which has led to a decline in vector populations. It is argued that this, together with a trend for Fulani and their cattle to become more sedentarised, has brought about a fundamental change in the balance of relationships in the vector-host-disease complex, which has favoured the development of appropriate immune responses in Fulani cattle, and the selection of less pathogenic strains of trypanosome.