Borrelia crocidurae Infection of Ornithodoros erraticus (Lucas, 1849) Ticks in Tunisia

Tick-borne relapsing fever (TBRF) is caused by Borrelia species transmitted to humans by infected Ornithodoros sp. ticks. The disease has been rarely described in North Africa, and in Tunisia the local transmission of TBRF seems to have disappeared or is undiagnosed. A longitudinal study was conducted in 14 sites located in four different bioclimatic zones of Tunisia to assess both the distribution of Ornithodoros sp. and their infection rate with the relapsing fever Borrelia sp. Three polymerase chain reaction methods targeting the 16S rRNA, the intergenic spacer, and the fla (flagellin) genes were used and phylogenetic analyses were carried out. Three hundred and fifty-eight specimens of Ornithodoros were collected: O. erraticus (previously termed small variety) (n = 190) and O. normandi (n = 168). Borrelia crocidurae DNA was detected in 15.1% of O. erraticus (small variety) (24 out of the 159 randomly selected for testing) collected in rodent burrows situated in the arid and Saharan areas in southern Tunisia. Molecular analysis targeting the 16S rRNA gene and the noncoding intergenic spacer domain showed good resolution for this Borrelia sp., although no molecular polymorphism was evidenced according to location. In contrast, none of the 133 O. normandi, also randomly selected for testing, was infected by Borrelia sp. and these ticks were restricted to the subhumid and semiarid zones in northern Tunisia. Both O. erraticus (small variety) and O. normandi were found in Tunisia and the high B. crocidurae infection rate found in O. erraticus highlights the risk of TBRF transmission in the southern part of the country.