ABSTRACT
In West Africa, tick-borne relapsing fever is due to the spirochete Borrelia crocidurae and its geographic distribution is classically limited to the Sahel and Saharan regions where the vector tick Alectorobius sonrai is distributed. We report results of epidemiologic investigations carried out in the Sudan savanna of Senegal where the existence of the disease was unknown. A two-year prospective investigation of a rural community indicated that 10% of the study population developed an infection during the study period. Transmission patterns of B. crocidurae to humans and the small wild mammals who act as reservoirs for infection were similar to those previously described in the Sahel region. Examination of 1,197 burrows and blood samples from 2,531 small mammals indicated a considerable spread of the known area of distribution of A. sonrai and B. crocidurae. The actual spread of the vector and the disease has affected those regions where the average rainfall, before the start of the extended drought in West Africa, reached up to 1,000 mm and corresponds to the movement of the 750-mm isohyet toward the south from 1970 to 1992. Our findings suggest that the persistence of sub-Saharan drought, allowing the vector to colonize new areas in the Sudan savanna of West Africa, is probably responsible for a considerable spread of tick-borne borreliosis in this part of Africa.
Subject(s)
Arachnid Vectors , Borrelia Infections/epidemiology , Desert Climate , Disasters , Disease Reservoirs , Adolescent , Adult , Animals , Borrelia Infections/transmission , Child , Child, Preschool , Eulipotyphla , Humans , Incidence , Infant , Middle Aged , Prospective Studies , Rain , Rodentia , Rural Population , Senegal/epidemiology , TicksABSTRACT
Tick-borne borreliosis in West Africa is classically considered a rare disease whose geographic distribution is limited to Saharan and Sahelian regions. We report results of epidemiological investigations which indicate that tick-borne borreliosis is endemic in all regions of Senegal north to the 13 degrees 30'N latitude and is a major cause of morbidity in these areas. Our findings indicate a considerable range extension for the vector tick Alectorobius sonrai and suggest that the persistence of Subsaharan drought is responsible for a large spread of tick-borne borreliosis in West Africa.
Subject(s)
Borrelia Infections/epidemiology , Adolescent , Adult , Africa, Western/epidemiology , Aged , Animals , Arthropod Vectors , Borrelia/isolation & purification , Borrelia Infections/diagnosis , Child , Child, Preschool , Demography , Humans , Incidence , Infant , Mice , Middle Aged , Rain , Rodentia/microbiology , Rodentia/parasitology , Ticks/microbiologyABSTRACT
We report results of a longitudinal survey designed to determine the importance and the dynamics of Borrelia crocidurae, the spirochete responsible for tick-borne relapsing fever in West Africa in rodents and insectivores in a rural area of northern Senegal. A total of 954 animals were caught during bimonthly capture sessions over a two-year period. Positive thick blood smears were recorded in 17.6% of the 740 rodents and 7.3% of the 55 musk shrews tested. Variations of prevalence were analyzed in Arvicanthis niloticus and Mastomys huberti, which represented 62.7% and 28.3%, respectively. of the animals captured, and 65.7% and 27.6%, respectively, of the animals found infected. Borrelia crocidurae prevalence was significantly different between captures and fluctuated separately for each species. Age-specific prevalence of B. crocidurae showed distinct patterns, decreasing with age from 50% in younger juveniles to 3% in older adults for A. niloticus, while increasing with age from 8% to 23% for M. huberti. No relationship was observed with animal abundance or with the season of the year for either species. These findings suggest that the diversity of the population dynamics of host-vector-parasite associations in the Sahel region of Senegal may be a key factor for the relative stability of the borreliosis reservoir.
Subject(s)
Borrelia Infections/veterinary , Borrelia/isolation & purification , Disease Reservoirs , Rodent Diseases/epidemiology , Shrews/microbiology , Age Factors , Animals , Borrelia Infections/epidemiology , Female , Gerbillinae , Longitudinal Studies , Male , Muridae , Prevalence , Rodentia , Rural Health , Seasons , Senegal/epidemiology , Sex FactorsABSTRACT
Reported cases of tick-borne relapsing fever due to the spirochaete Borrelia crocidurae are rare in West Africa, and few epidemiological data are available. To see how common relapsing fever is in Senegal thick blood smears from cases of fever of unknown origin and from randomly selected clinic outpatients from a rural dispensary were examined for Borrelia. The prevalence of Borrelia infections in small mammals was also assessed. Borrelia was seen in smears of 12 (0.9%) of 1340 children. All children who tested positive had complained of acute fever. Prevalence was 0% (0/496), 0.5% (2/417), 1.6% (5/308), and 4.2% (5/119) at ages 0-1, 2-4, 5-9, and 10-14, respectively. 26 other instances of borreliosis were seen in patients from different regions of Senegal. Blood samples from 7 of these patients were inoculated intraperitoneally into white mice; serious infection developed in all mice. Borrelia was seen in thick smears from 65 of 461 wild rodents or insectivores. Six rodents species were infected. From a sample of 93 rodents, 33.3% were infected, as judged by intraperitoneal inoculation of white mice, compared with 14.1% by direct smear examination. The findings suggest that borreliosis has a wide distribution and a high incidence in Senegal. This disease may be a major cause of morbidity in rural areas throughout much of West Africa.
