Tick-borne relapsing fever (RF) in the civilian population of Israel, 1980 2002

Abstract:
Tick-borne relapsing fever (RF) is considered to be caused by the spirochaete Borrelia persica, transmitted to humans by Ornithodorus tholozani, and is a notifiable disease in Israel. Between 1980 and 2002, 184 cases were reported, i.e. an average of eight cases per year (range 0-16). Among them, about 50% were children and more than 80% were day-trippers. The infestation foci were principally caves. Many of the foci are sites in, or near the periphery of, urban areas where it is easy for people to visit them. Professional visitors working in caves were rarely infected, since they generally take preventive measures against tick bites. The distribution of the disease is all over the country except the southern Negev Desert. This also indicates the distribution of O. tholozani. Tick samples were collected in several locations from which clinical cases were reported. Partial sequences of the 18S rDNA were amplified by PCR and sequenced. The analysis of a 600 bp fragment by blast gave 84% homology with Ornithodorus moubata. DNA extracts of a pool of ticks and of patients’ blood samples were successfully amplified and produced an approximately 780 bp fragment of the flagellin gene of Borrelia. Sequence similarity was more than 99% with RF strain species and 85% with Lyme borreliosis species. Taxonomic analysis showed that sequences of the Israeli RF Borrelia clustered in a separate group from the American and the African RF species. This is the first report of molecular characterization of the etiologic agent of RF and its tick vector in the Middle East. The exact taxonomic link to the previously described B. persica requires further study.