Background & Objective: Ardabil province is the main area of Iran affected by relapsing fever (RF) for which Borrelia Persica is the most common cause. The aim of this study was to determine the epidemiologic characteristics of the disease, and the frequency of infection among ticks in this region in order to take necessary measures to decrease it is incidence and increase awareness about the characteristics of this disease.

 Method: In this study a total of 391 patients who were diagnosed to have been effected by tick borne relapsing fever were investigatated in terms of clinical epidemiology between 1998 and 2001. The kind of Borrelia as well as the clinical characteristics of the disease were observed. The kind and prevalence of Borrelia infection was determined in 1,421 ticks collected from 130 indoor and 14 outdoor sites. The ticks were crushed and the suspension obtained was injected into the peritoneum of two mice and two guinea pigs to determine the frequency of infection among the ticks living in this region. Data including the tick species determination were collected through a questionnaire and analyzed using Chi-square and ANOVA tests.

 Results: The most prevalent clinical manifestations were fever, chills and headache. Other findings included nausea, vomiting, sweating, abdominal pain, arthralgia, cough, photophobia, eosinophilia, hematuria, jaundice, petechiae and sclera congestion. Laboratory tests performed on 60 patients showed leukocytosis, high erythrocyte sedimentation rate (ESR) and anemia. Of the 1,421 ticks collected, 45.9%, 40.3% and 13.8% were infected by Ornithodoros lahorensis Ornithodoros tholozani and Argas persicus species, respectively. The prevalence of ticks was highest in Khanadabil village. The ticks collected from three villages were found to be infected with Borrelia.

 Conclusions: The clinical manifestations were similar to those reported in other studies. Petechiae occurred less frequently in our study compared to louse-borne RF. The high frequency of anemia in this region, which was not stated in other reference articles, requires further investigation.