The effect of transhumance on the epidemiology of animal diseases

Abstract

Transhumance, the seasonal movement of people and their livestock to regions of different climate is a way of life for tens of millions of people living in the cool mountainous or the arid and semi-arid regions of the world. Transhumant peoples migrate through and spend most of the time in areas where there are invariably no veterinary, medical or educational facilities, nor abattoirs, safe water supplies or sanitation. Prevalent diseases go unrecorded and there are rarely any attempts made at disease control. The epidemiology of different diseases in transhumant communities is additionally influenced by their peculiar animal husbandry practices, the different species of livestock maintained, the close association of humans and their livestock and the small isolated groups and their frequent migrations. The frequency of these migrations will remove them from the build-up of free-living parasites including most of the faecally transmitted protozoans and helminths and also from the huge numbers of nuisance flies. Migrations, however, increase their chances of coming into contact with geographically limited or seasonally abundant diseases. In Africa, these include, Trypanosoma spp. and Cowdria ruminantium, which have a profound effect on migration patterns. Migrations also increase the opportunity for the interaction of domestic and wild animals, which facilitates the transmission of a number of shared diseases, particularly bacterial, viral, rickettsial and protozoan infections. Temperature and relative humidity play an important role in determining the distribution of those parasite species which have free-living forms or have indirect life cycles, particularly those involving invertebrate hosts. The relative importance of all the above factors on the epidemiology of different parasite species found in the cold and/or arid regions of the world occupied by transhumant peoples and their livestock is discussed.