A comparative study of three methods of detection of Borrelia crocidurae in wild rodents in Senegal

In a rural area in Sénégal with a high incidence of tick-borne relapsing fever in humans, Borrelia crocidurae was studied in the blood and brain of wild rodents (Mastomys erythroleucus, Arvicanthis niloticus and Rattus rattus) using 3 methods: (i) direct examination of thick blood films; (ii) intraperitoneal inoculation of blood into white mice; (iii) intraperitoneal inoculation of homogenized cerebral tissue into white mice. Of the 82 rodents examined, the proportion of infected animals was respectively 2.4%, 7.3% and 14.6% for each method, and 18.3% for all 3 methods combined. Of the 12 animals with infected cerebral tissue, only 3 were found to have infected blood. These results suggest that isolated infections of the brain occur frequently in Senegalese wild rodents. Measurement of the real prevalence of B. crocidurae should therefore take into account these infections in addition to blood infections.