Rickettsia africae infection rates and transovarial transmission in Amblyomma hebraeum ticks in Mnisi, Bushbuckridge, South Africa.

Rickettsia africae is a gram-negative bacterium, which causes African tick bite fever (ATBF) in humans. ATBF is a febrile disease mainly affecting travellers to southern Africa. This bacterium is known to be transmitted by Amblyomma hebraeum and Amblyomma variegatum ticks. In southern Africa, the principal vector is A. hebraeum. Febrile disease is a serious issue in the study area. There is a high prevalence of non-malaria illness caused by Rickettsia, so there is a need to have more knowledge on these species. Infection rates and transovarial transmission efficiency of R. africae in A. hebraeum ticks were investigated in a rural area of Mpumalanga province, South Africa. Adult and engorged A. hebraeum female ticks were collected from cattle. Larvae were collected by dragging a cloth at ground level using 100 steps, equivalent to an area of 100 m2. Tick identification was performed according to standard taxonomic keys using a microscope. Engorged ticks were incubated to oviposit and egg masses were collected. DNA was extracted from the ticks, larvae and egg masses, and screened for gltA and ompA genes, using quantitative real-time PCR and conventional PCR, respectively. Positive ompA amplicons were sequenced and phylogenetic analysis showed 99.8-100% identity with R. africae. Infection rates were 13.7 and 12.7% for adults and larvae, respectively. Transovarial transmission of R. africae in A. hebraeum from this study was 85.7%. The results provide a clear indication that people living in the study area and travellers that visit the area are at risk of contracting ATBF.

Rickettsia africae: identifying gaps in the current knowledge on vector-pathogen-host interactions.

Rickettsia africae is a bacterium of zoonotic importance, which causes African tick bite fever (ATBF) in humans. This pathogen is transmitted by ticks of the genus Amblyomma, with Amblyomma hebraeum and Amblyomma variegatum being the major vectors. Tick species other than the above-mentioned have also been reported to carry R. africae DNA. There is scarcity of information on the epidemiology of this pathogen, yet several cases have been recorded in foreign travellers who visited endemic areas, especially southern Africa. The disease has rarely been described in people from endemic regions. The aim of this study was to discuss the information that is currently available on the epidemiology of R. africae, highlighting the gaps in this field. Furthermore, ATBF cases, clinical signs and the locations where the cases occurred are also listed in this review.