Tickborne relapsing fever in Israel

We evaluated the epidemiology of relapsing fever from 1971 to 2003 in Israel. In civilians, incidence declined from 0.35 to 0.11 cases per 100,000 persons annually; in military personnel it averaged 6.4 cases per 100,000 persons annually. These data imply that the pathogen and vector continue to exist in Israel.     

Tick-borne relapsing fever in central Tanzania

Between October 1985 and September 1986, 488 children aged less than 15 years, 45 pregnant women, 21 other women and 18 men with tick-borne relapsing fever (TBRF) were seen at Mvumi Hospital, Central Tanzania. 88% of the children were less than 5 years old and 36% were less than 1 year. Twelve children were less than 1 month old and some of the 10 infants diagnosed at between 4 and 12 days of age were cases of congenital infection. The clinical features of TBRF in the children and pregnant women were compared with 129 children with a similar age distribution and 52 pregnant women, respectively, who had blood smears positive for malaria but negative for spirochaetes. The common presenting features in children with TBRF were a high fever, splenomegaly, convulsions, and meningism. The difficulty of differentiation from malaria is described. Severe disease in both children and adults was associated with high density of spirochaetes in blood smears. Of the 45 infected pregnant women, 22 (49%) went into labour. One of the deliveries was an abortion and 10 were preterm infants, 4 of whom died. There were no maternal deaths. The estimated overall mortality for children was 1.6%, and 2.3% for those aged less than 1 years; for the 95 children admitted it was 8.4%. Penicillin was a satisfactory treatment for all ages, with a relapse rate of 4.7%. Recommendations for patient management are given.     

Possibilities for relapsing fever reemergence

Relapsing fever Borrelia infections have attracted little attention in recent years; however, where endemic, these infections still result in considerable illness and death. Despite the marked antimicrobial drug susceptibility of these organisms, therapy is often delayed through lack of clinical suspicion. With increasing travel, infections may be imported, through exotic relapsing fever infection or through resurgence of infected disease vectors. Although louseborne relapsing fever is now geographically limited, it was once of global importance. The possibility for reemergence was recently highlighted by the probable reemergence of louseborne relapsing fever in homeless persons from France. Host limitations enforced through louseborne transmission are less applicable for the tickborne forms of relapsing fever. Although the latter have reduced potential for epidemic spread, they have the ability to infect diverse hosts, thus establishing reservoirs of infection and presenting greater challenges for their control.     

Typing African relapsing fever spirochetes

Relapsing fever Borrelia spp. challenge microbiologic typing because they possess segmented genomes that maintain essential genes on large linear plasmids. Antigenic variation further complicates typing. Intergenic spacer (IGS, between 16S-23S genes) heterogeneity provides resolution among Lyme disease-associated and some relapsing fever spirochetes. We used an IGS fragment for typing East African relapsing fever Borrelia spp. Borrelia recurrentis and their louse vectors showed 2 sequence types, while 4 B. duttonii and their tick vectors had 4 types. IGS typing was unable to discriminate between the tick- and louseborne forms of disease. B. crocidurae, also present in Africa, was clearly resolved from the B. recurrentis/B. duttonii complex. IGS analysis of ticks showed relapsing fever Borrelia spp. and a unique clade, distant from those associated with relapsing fever, possibly equivalent to a novel species in ticks from this region. Clinical significance of this spirochete is undetermined.