The epidemiology of leishmaniasis in Baringo and Machakos Districts with emphasis on animal reservoirs
Identification of animal reservoirs of leishmaniasis is an absolute pre-requisite to understanding the epidemiology of the disease. A 16-month search for animal reservoirs of leishmaniasis began in Marigat Location of Baringo District in May 1986 and in Masinga Location of Machakos District in December 1987. Epidemics were reported in these areas during the 1950s and 1970s and current endemicity of the disease suggest that animal reservoirs maintain the infection. Examination for leishmanial parasites was done, using culture and smear techniques. From Marigat, a total of 1,128 rodents belonging to 7 genera and 11 carnivores belonging to 3 genera were examined; and from Masinga, 633 rodents belonging to 10 genera and 95 carnivores belonging to 5 genera were examined. From Marigat, 3 (0.5%) Arvicanthis niloticus, 36 (12.5%) Tatera robusta and 2 (0.8%) Mastomys natalensis were positive for leishmanial parasites. From Masinga, no leishmania infection was detected but 67 (60.4%) Acomys subspinosus, 12 (8.4%) Mastomys natalensis, 2 (4.0%) Lemniscomys striatus, 2 (33.3%) Herpestes sanguineus, 1 (100%) Helogale parvula and 1 (1.2%) Canis familiaris were found positive with trypanosome flagellates. Forty-two isolates from sandflies, 34 from humans and 13 from lizards all obtained from the study sites were included for comparlson with isolates from wild animals. All isolates were characterized by isoenzyme analysis using nine enzymes. The enzymes examined were: malate dehydrogenase (MDH), phosphoglucomutase (PGM), glucose phosphate isomerase (GPl), isocitrate dehydrogenase (leD), nucleoside hydrolase (NH), glucose 6-phosphate dehydrogenase (G6PD), malic enzyme (ME), 6-phosphogluconate dehydrogenase (6PGD) and mannose phosphate isomerase (MPl). The isolates were compared with five Old World Leishmania reference strains and five well characterized rodent trypanosomes of the subgenus Herpetosoma. All the isolates from rodents In Marigat (except one from a Mastomys) were identified as Leishmania major. Of the 34 isolates from humans, 31 were identified as L. donovani and three as ~. major. Thirty-four isolates from Sergentomyia spp. and 13 from lizards were all identified as L. adleri. Five P. duboscqi and 3 P. martini isolates were identified as L. major and donovani respectively. All the isolates from animals from Masinga and one from a Mastomys from Marigat differed from the Leishmania reference strains. They were, however, morphologically similar to rodent trypanosomes. The enzyme profiles of the three mongoose isolates were identical to each other but different from rodent and dog isolates. The results of the studies in Marigat suggest that rodents are the reserVOlrs of cutaneous leishmaniasis 1n Baringo District, with Tatera robusta serving as the main reservolr. Leishmania major was not isolated from animals in Masinga. The prevalence of mammalian trypanosome flagellates was very high in Acomys (60.4%) collected in Masinga but in Marigat, only one Mastomys (0.004%) was found infected with trypanosome flagellates. Mastomys and Acomys were found to be susceptible to experimental infection with L. donovani while dogs, cats and goats were found to be refractory to the infection. Although rodents were susceptible, none were found naturally infected with 1. donovani. The results in this study argue against the notion that wild mammals and/or dogs serve as reservoirs of visceral leishmaniasis and support the suspicion that man is probably the only reservoir of infection in Kenya.