The epidemiology of tick-borne relapsing fever in Iran during 1997–2006

Abstract

Tick-borne relapsing fever is an acute febrile and endemic disease in Iran. For many reasons, the incidence of disease is on decrease, however tick-borne relapsing fever is still a health issue in the rural areas for travelers. This study was carried out during 1997-2006 to investigate the tick-borne relapsing fever in Iran. Based on a cross-sectional, retrospective and descriptive study in all the provinces, the residents in the endemic areas who were febrile and suspicious to tick-borne relapsing fever were enrolled in the study. Tick-borne relapsing fever is a notifiable disease in Iran and the national communicable disease surveillance data were used through questionnaires. The infectivity of Ornithodoros species to Borrelia also was studied in two highly endemic areas including Hamadan and Qazvin provinces. During 1997-2006, a total of 1415 cases have been reported from the entire country. The highest prevalence was observed in year 2002 with the incidence rate of 0.41/100,000 population. Ardabil province is the first ranked infected area (625 out of 1415), followed by Hamadan, Zanjan, Kurdestan and Qazvin provinces sequentially. The disease is recorded during the whole year but its peak occurs during summer and autumn. There have been 87.6% of the cases recorded from June to November. Forty five percent of the infected cases were male and one third of the patients were under 5 years of age. Fifty four percent of the patients comprise the children under 10 years. Ninety two percent of the cases were living in rural areas where their dwellings were close to animal shelters. They were involved mainly with farming and animal husbandry activities. All the febrile patients with confirmed spirochetes in their blood samples were treated according to a national guideline for tick-borne relapsing fever treatment. Only 7% of the patients were hospitalized and 0.8% of them exhibited the Jarisch-Herxheimer reaction. The study of infectivity of Ornithodoros species to Borrelia revealed that Ornithodoros tholozani was infected with Borrelia persica and Ornithodoros erraticus with Borrelia microti. Travelers to the rural areas with high prevalence of the disease should be made aware of the risk of tick-borne relapsing fever and use of appropriate control measures. Communicable disease surveillance including tick-borne relapsing fever should be pursued as well.