The Surveillance of Rodent Populations in East Africa in Relation to Plague Endemicity

Abstract

Plague has been endemic in East Africa from very early times. The fact that the plague organism occurring in the area is mostly Pasteurella pestis var. antiqua which is said to have been associated with the Justinian pandemic of the 6^th century A. D. would seem to support the contention that this endemicity was established during that pandemic. The maintenance of this endemicity has been made possible by the presence in the area of suitable rodent reservoirs, efficient flea vectors and favourable climatic and ecological conditions. The main reservoirs of plague in East Africa are Rattus rattus, Praomys natalensis and Arvicanthis abyssinicus. Because of their semi-domestic habits, P. natalensis and A. abyssinicus are usually responsible for carrying plague during plague epizootics from the field to the domestic environment where R. rattus plays a major role. In the plague areas investigated in Tanzania, P. natalensis and A. abyssinicus formed the bulk of the field rodent population. It is possible that Tatera species play some role in those endemic areas where they occur. However, the absence of these rodents from some of the plague areas would seem to suggest that their presence is not necessary for the maintenance of plague endemicity. The main flea vectors of plague in East Africa are Xenopsylla cheopis, X. brasiliensis and Dinopsyllus lypusus. The fact that in endemic areas all these three flea species occur commonly on the main rodent reservoirs R. rattus, P. natalensis and A. abyssinicus indicates the close association in which these three rodents live with one another. This close association is favourable for plague transmission.