SEROLOGICAL SURVEY OF PLAGUE IN RODENTS AND OTHER SMALL MAMMALS IN KENYA

During a survey from 1963 to 1966 over 8000 sera from rodents and other animals from different parts of Kenya were tested for HA antibodies to the fraction 1 antigen of P. pestis. HA antibodies were present in high titre (1 in 512 to 1 in 2048) in sera from Arvicanthis niloticus, Praomys natalensis, Rattus rattus, and Acomys spp. and in lower but significant titres (1 in 16 in 256) in sera from Otomys angoniensis, Aethomys kaiseri, Tatera spp. Lemniscomys striatus, L. griselda and Rhabdomys pumilio. Serum from a Thamnomys dolichurus reacted at 1 in 256. Other animals tested included a few genet cats (Genetta tigrina), bush squirrels (Paraxerus ochraceus) dwarf mongooses (Helogale parvula), an African striped polecat (Ictonyx striatus) and a giant elephant shrew (Petrodromus tetradactylus); of these, sera from a Helogale reacted at 1 in 32 and from a Petrodromus at 1 in 256; the other animals were negative. In 1962–1965 10% of the sera were positive and in 1966 only 6%. The percentage of sera positive in 1962–1965 was very high at Kisumu (41%) and at Taveta (42%); at Rongai only 2%. Quite high positive rates were found at Kombeni and Mombasa (both 13%), and at Malindi (16·5%). The positive rate in the Nairobi area was 7%; in 1966 this had fallen to 1%. Since 1950 human plague has occurred sporadically in the Nairobi area (Kiambu in 1952), at Rongai (1952, 1954) and at Konza (1953) near Masaku. It was not uncommon at Nyeri, but a serological survey remains to be done. There are grounds for believing that the permanent reservoir of plague is frequently associated with foothill areas, at medium altitudes. This does not account, however, for its evident persistence in such low-lying coastal areas as Mombasa, Kombeni and Malindi. The HA test is reliable. It remains to explain the persistence of P. pestis in the absence of overt signs of plague by isolating and studying strains from different localities, when the serological results indicate its continued existence. © 1968 Royal Society of Tropical Medicine and Hygiene.