oa South African Medical Journal - A plague survey of Ngamiland, Bechuanaland Protectorate, during the epidemic of 1944-45 (concluded)

Abstract

Rodent plague. -The unusually favourable season of 1943-4 culminating in the Okavango floods stimulated rodent life in general to reach a high density. Plague broke out in the wild reservoir gerbil population early in 1944, giving rise to secondary epizootics amongst multimammate mice during the winter. These mice died in large numbers in and about the native kraals throughout Ngamiland towards the end of the winter and gave rise in turn to the human epidemic. Human Plague.-The epidemic was practically confined to the Lake Ngami, Makalamabedi and Rakops areas and was most active in October and November. Sporadic outbreaks continued at Rakops until March, 1945. The majority of cases were of bubonic plague, some were of septicaemic plague and a few were of pneumonic plague (at Rakops and on the river road to Makalamabedi). The majority of the cases were contracted from the bites of infective fleas in and about the huts, but it is impossible to rule out certain veld sources of infection entirely infection entirely. Rodent and Flea Fauna.-The chief wild rodent reservoir of plague is in gerbils (Tatem spp.). The intermediary between gerbils and man is the multimammate mouse (Mastomys coucha). The fleas responsible for the spread both amongst rodents and from rodents to man are Xenopsylla eridos, X. hipponax and X. brasiliensis. The part played by Y. hipponax is uncertain, and for the time being it is classed with its close relative X. eridos. The first two species parasitise gerbils, and all three were found on multimammate mice, whether captured in huts or in the veld. X. Brasiliensis was almost certainly responsible for the majority of the human infections. Its wild hosts are tree-rats (Thallomys), golden rats (lEthomys namaquensis) and African rats (A. chrysophilus). There is no record of the presence of the introduced domestic rodents, the house-rat (Rattus rattus) or the house-mouse (Mus musculus) in Bechuanaland.