Abstract
BackgroundTick-borne relapsing fever spirochetes are maintained in endemic foci that involve a diversity of small mammals and argasid ticks in the genus Ornithodoros. Most epidemiological studies of tick-borne relapsing fever in West Africa caused by Borrelia crocidurae have been conducted in Senegal. The risk for humans to acquire relapsing fever in Mali is uncertain, as only a few human cases have been identified. Given the high incidence of malaria in Mali, and the potential to confuse the clinical diagnosis of these two diseases, we initiated studies to determine if there were endemic foci of relapsing fever spirochetes that could pose a risk for human infection.Methodology/Principal FindingsWe investigated 20 villages across southern Mali for the presence of relapsing fever spirochetes. Small mammals were captured, thin blood smears were examined microscopically for spirochetes, and serum samples were tested for antibodies to relapsing fever spirochetes. Ornithodoros sonrai ticks were collected and examined for spirochetal infection. In total, 11.0% of the 663 rodents and 14.3% of the 63 shrews tested were seropositive and 2.2% of the animals had active spirochete infections when captured. In the Bandiagara region, the prevalence of infection was higher with 35% of the animals seropositive and 10% infected. Here also Ornithodoros sonrai were abundant and 17.3% of 278 individual ticks tested were infected with Borrelia crocidurae. Fifteen isolates of B. crocidurae were established and characterized by multi-locus sequence typing.Conclusions/SignificanceThe potential for human tick-borne relapsing fever exists in many areas of southern Mali.
Highlights
The epidemiology of tick-borne relapsing fever was founded on the works of several independent investigators working across central Africa during the first decade of the 20th century
David Livingstone is credited with the first written account in 1857 of a malady associated with the bite of soft ticks in areas known as Angola and Mozambique [1], the identity and route of transmission of the etiological agent were not discovered for another 45 years
We investigated 20 villages across southern Mali to determine if relapsing fever spirochetes were circulating in small mammals and ticks that lived with people
Summary
The epidemiology of tick-borne relapsing fever was founded on the works of several independent investigators working across central Africa during the first decade of the 20th century. Congo Free State ( the Democratic Republic of Congo) [10] Both men contracted the infection while performing autopsies, and Dutton died there on February 27, 1905 [3]. The spirochete that caused tick-borne relapsing fever across central Africa was named Spirillum Duttoni [11], named Borrelia duttonii [12], to honor Dutton’s contributions and sacrifice while working on tick fever and other tropical diseases including malaria and trypanosomiasis. Given the high incidence of malaria in Mali, and the potential to confuse the clinical diagnosis of these two diseases, we initiated studies to determine if there were endemic foci of relapsing fever spirochetes that could pose a risk for human infection
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