Relapsing fever borreliosis in Eurasia—forgotten, but certainly not gone!

Abstract

Tick-borne relapsing fever (TBRF) has been reported in Eurasia and attributed mainly to Borrelia persica, although other entities have also been described. Ornithodoros tholozani is the most important tick vector, found in India and Kashmir, the southern countries of the former USSR, Iran, Iraq, Syria, Jordan, Turkey, Israel, Egypt, and Cyprus. It inhabits caves, ruins, and burrows of rodents and small mammals. In the northern countries, O. tholozani also lives in houses and cowsheds. In Israel, 30-60% of caves were found to be infested. PCR studies of Borrelia infection of O. tholozani ticks collected in caves showed very variable rates, ranging from less than 2% to 40%. The number of human cases reported varies among countries, from eight cases per year in Israel to 72 cases per year in Iran. The incubation period is 5-9 days. The fever attacks last from several hours to 4 days, and are accompanied by chills, headache, nausea and vomiting, sweating, abdominal pain, arthralgia, and cough; complications are rare. Other described Borrelia species are Borrelia caucasica, Borrelia latyschewii, Borrelia microtii, and Borrelia baltazardi. The classic taxonomy based on the co-speciation concept is very complex and very confusing. For this reason, 16S rRNA and flaB genes were used for taxonomic clarification. Sequencing of Israeli TBRF flaB genes, from human and tick samples, has demonstrated a third cluster corresponding to the Eurasia strains, in addition to both New World and Old World clusters. Thin and thick blood smears remain the most frequently used methods for laboratory diagnosis, with a sensitivity of 80%. PCR-based diagnosis is the most sensitive method, and has the advantage of allowing species identification.