A decade of plague epidemiology and control in the Western Usambara mountains, north-east Tanzania

Abstract

Outbreaks of human plague have been occurring in the Western Usambara mountains since 1980, involving many cases and deaths. Epidemiological surveys and control activities were carried out from June 1980 to May 1990. Rodents were trapped live, identified and serologically tested for plague, using the passive haemagglutination and passive haemagglutination inhibition tests. Rodent fleas were collected, processed, identified and counted. House fleas were caught with light traps and similarly treated. People and domestic carnivores were serologically tested for the disease. Various plague control measures were undertaken. A total of 2433 animals, 2254 rodent fleas and 1366 house fleas were collected. Average indices of rodent and house fleas were 0.93 and 5.38 respectively. Rattus rattus and Mastomys natalensis were the most abundant rodent species. Xenopsylla brasiliensis and Dinopsyllus lypusus were their commonest flea ectoparasites while Pulex irritans was the major house flea. Of 2044 rodent, 1880 human and 176 dog sera tested, 5.5%, 0.5% and 6.3% respectively were positive. It was concluded that plague was active in the focus despite the control measures and that common reservoirs and efficient vectors were present. It was suggested that dogs were probably involved in the epidemiology of the disease, that P. irritans was not susceptible to the insecticide used and that the flea was probably involved in murine plague transmission. Bacteriological research on the causative agent to establish the nature of its long persistence in the area and maintenance of a surveillance service are recommended.