Abstract
BackgroundRickettsioses are one of the most important causes of systemic febrile illness among travelers from developed countries, but little is known about their incidence in indigenous populations, especially in West Africa.Methodology/Principal FindingsOverall seroprevalence evaluated by immunofluorescence using six rickettsial antigens (spotted fever and typhus group) in rural populations of two villages of the Sine-Saloum region of Senegal was found to be 21.4% and 51% for spotted fever group rickettsiae for Dielmo and Ndiop villages, respectively. We investigated the role of tick-borne rickettsiae as the cause of acute non-malarial febrile diseases in the same villages. The incidence of rickettsial DNA in 204 blood samples from 134 (62M and 72F) febrile patients negative for malaria was studied. DNA extracted from whole blood was tested by two qPCR systems. Rickettsial DNA was found in nine patients, eight with Rickettsia felis (separately reported). For the first time in West Africa, Rickettsia conorii was diagnosed in one patient. We also tested 2,767 Ixodid ticks collected in two regions of Senegal (Niakhar and Sine-Saloum) from domestic animals (cows, sheep, goats, donkeys and horses) by qPCR and identified five different pathogenic rickettsiae. We found the following: Rickettsia aeschlimannii in Hyalomma marginatum rufipes (51.3% and 44.8% in Niakhar and Sine-Saloum region, respectively), in Hyalomma truncatum (6% and 6.8%) and in Rhipicephalus evertsi evertsi (0.5%, only in Niakhar); R. c. conorii in Rh. e. evertsi (0.4%, only in Sine-Saloum); Rickettsia massiliae in Rhipicephalus guilhoni (22.4%, only in Niakhar); Rickettsia sibirica mongolitimonae in Hyalomma truncatum (13.5%, only in Sine-Saloum); and Rickettsia africae in Rhipicephalus evertsi evertsi (0.7% and 0.4% in Niakhar and Sine-Saloum region, respectively) as well as in Rhipicephalus annulatus (20%, only in Sine-Saloum). We isolated two rickettsial strains from H. truncatum: R. s. mongolitimonae and R. aeschlimannii.Conclusions/SignificanceWe believe that together with our previous data on the high prevalence of R. africae in Amblyomma ticks and R. felis infection in patients, the presented results on the distribution of pathogenic rickettsiae in ticks and the first R. conorii case in West Africa show that the rural population of Senegal is at risk for other tick-borne rickettsioses, which are significant causes of febrile disease in this area.
Highlights
Cases of tick-borne rickettsiosis have been regularly reported in North [1] and South Africa [2,3] since 1910
We have studied the distribution of bacteria causing different spotted fevers in rural Senegal, as well as the role of these bacteria in human pathology among indigenous population
We have found that up to half of tested villagers have serological evidence of contact with rickettsiae and in some cases these bacteria may be found in the blood of feverish patients
Summary
Cases of tick-borne rickettsiosis have been regularly reported in North [1] and South Africa [2,3] since 1910. Multiple cases of the disease and isolations of the agent have been reported, mostly in countries in the Mediterranean region. In 1992, a case of another spotted fever group (SFG) rickettsiosis in a 36-year-old woman presenting with tick bite fever at a hospital in Zimbabwe was described [8]. R. africae seems to be very widely distributed in the continent It has been either isolated or found by PCR in a number of African countries, including Niger, Mali, Burundi, Sudan [12], Chad, Ethiopia [13], and in most countries of equatorial and Southern Africa [14]. Rickettsioses are one of the most important causes of systemic febrile illness among travelers from developed countries, but little is known about their incidence in indigenous populations, especially in West Africa
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