African tick bite fever is a rickettsiosis of the spotted fever group that is endemic to sub-Saharan Africa and the Caribbean. It is characterized by eschars at the inoculation sites and a maculopapular rash which may be purpuric. We describe three cases that were diagnosed in Quebec City.

Rickettsia africae is a tick-borne bacteria known to cause African tick bite fever (ATBF). While the disease was first described more than 100 years ago, knowledge of transmission risk factors and disease burden remain poorly described. To better understand the burden of R. africae, this article reviewed and summarized the published literature related to ATBF epidemiology and clinical management. Using a systematic approach, consistent with the PRISMA guidelines, we identified more than 100 eligible articles, including 65 epidemiological studies and 41 case reports. Most reports described R. africae in ticks and livestock, while human studies were less common. Human disease case reports were exclusively among returning travellers from non-endemic areas, which limits our disease knowledge among at-risk populations: people living in endemic regions. Substantial efforts to elucidate the ATBF risk factors and clinical manifestations among local populations are needed to develop effective preventative strategies and facilitate appropriate and timely diagnosis.

African tick bite fever, an acute febrile illness, is caused by the obligate intracellular bacterium Rickettsia africae. Immune responses to rickettsial infections have so far mainly been investigated in vitro with infected endothelial cells as the main target cells, and in mouse models. Patient studies are rare and little is known about the immunology of human infections. In this study, inflammatory mediators and T cell responses were examined in samples from 13 patients with polymerase chain reaction-confirmed R. africae infections at different time points of illness. The Th1-associated cytokines IFNγ and IL-12 were increased in the acute phase of illness, as were levels of the T cell chemoattractant cytokine CXCL-10. In addition, the anti-inflammatory cytokine IL-10 and also IL-22 were elevated. IL-22 but not IFNγ was increasingly produced by CD4+ and CD8+ T cells during illness. Besides IFNγ, IL-22 appears to play a protective role in rickettsial infections.

African tick bite fever (ATBF) is one of the most important rickettsial infections in international travellers to sub-Saharan Africa. The heterogeneity of Rickettsia africae infection rates among tick vector species has been studied. However, this information has not been systematised to allow for comparative estimates. Quantifying the trends and heterogeneity in R. africae infection rates among the different tick vector species is paramount in understanding the role in transmission to humans. A systematic search was conducted in PubMed, Web of Knowledge, Google Scholar, and SCOPUS from 2005 to 2020. The selection criteria included all studies in sub-Saharan Africa reporting R. africae infection rates in tick adults, nymphs, and larvae. A quality effects model was used in the meta-analysis due to the observed heterogeneity with an assessment of publication bias using funnel plots. The prevalence estimates were conducted by geographic region and tick genus from 32 studies reporting R. africae infection rates in ticks from sub-Saharan Africa. A total of 12,301 ticks comprising of adults (96.19%, n=11, 832), nymphs (3.6%, n=443) and larvae (0.2%, n=26) and 1214 pooled samples were evaluated for R. africae infection. The overall prevalence of R. africae was higher in Amblyomma spp. (48%, 95% CI: 26-70%) compared to Rhipicephalus spp. (1%, 95% CI: 0-5%), Hyalomma spp. (1%, 95% CI: 0-3%) and other tick genera (1%, 95% CI: 0-4%) throughout all regions. The highest prevalence in Amblyomma spp. was recorded in western Africa (53%, 95% CI: 14-90%) and in Rhipicephalus spp. in southern Africa (2%, 95% CI: 0-5%). Cattle were the most frequently sampled hosts across all tick vectors (62.98%, n=5492), followed by goats (19.07%, n= 1663) and sheep (9.1%, n= 793). To our knowledge, this is the first systematic and quantitative analysis of R. africae infection in tick vectors collected from mammalian hosts in sub-Saharan Africa. The results highlight a marked heterogeneity between species in different regions of sub-Saharan Africa and provide initial estimates of infection rates.

African tick bite fever (ATBF) is an acute febrile illness caused by Rickettsia africae. ATBF is an important differential diagnosis of acute febrile illness among returned travelers. However, little information is available on ATBF cases imported to Japan, as only seven have been reported to date. To characterize the epidemiological and clinical profiles of patients diagnosed with ATBF in Japan, we reported three new ATBF cases at our hospital between May 2015 and April 2018 and conducted a literature review.

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 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.

Background: Ticks transmit a plethora of pathogens of zoonotic implications. Their distribution, diversity and the pathogens they transmit differ from one ecological location to another. Rickettsia africae is the agent of African tick bite fever found in South Africa, a zoonotic infection that is frequently reported among travelers who have visited many sub-Saharan African countries where the pathogen is prevalent. Methods: Ticks were collected from domestic animals in Raymond Nkandla Municipality, Eastern Cape, South Africa. The ticks were identified morphologically prior to DNA extraction followed by molecular identification of randomly selected ticks from the morphologically delineated groups. To assess for the presence of tick-borne pathogens belonging to Rickettsia spp. by PCR (polymerase chain reaction), we used specific primer pairs targeting the gltA, ompA and ompB genes. The selected amplified ticks, all positive ompB and forty three ompA amplicons were sequenced in a commercial sequencing facility. The obtained nucleotide sequences were edited and subjected to BLASTn for homology search and phylogenetic analyses were performed with MEGA 7 Version for genetic relationships with curated reference sequences in GenBank. Results: A total of 953 ticks collected in the study were delineated into three genera consisting of Amblyomma, Rhipicephalus and Hyalomma in decreasing order of abundance. The presence of rickettsial DNA was detected in 60/953 (6.3%) from the three genera of ticks screened. Genetic analyses of the DNA sequences obtained showed that they have phylogenetic relationship to members of the spotted fever group rickettsiae with R. africae, being the predominant SFGR (spotted fever group rickettsiae) detected in the screened ticks. Conclusion: This report shows that R. africae is the predominant spotted fever group rickettsiae in ticks collected from domestic animals in the study area and the human health impacts are not known.

African tick bite fever (ATBF) is a tick-borne rickettsial disease most often observed in North American and European tourists returning home from the southern portion of Africa. Ticks infected with Rickettsia africae transmit this parasitic bacterium to humans, who subsequently develop an influenza-like illness, one or more inoculation eschars, and in some cases, a cutaneous rash. Because ATBF often presents with non-specific symptoms that suggest other infectious diseases, establishing the diagnosis may be difficult. Confirmatory assays, including serology and nucleic acid amplification, may take weeks to return and cannot help with acute treatment decisions. We present a case of a previously healthy 60-year-old woman who developed an illness strongly suggestive of ATBF after a missionary trip to Zimbabwe and discuss the disease\'s diagnostic challenges. Our paper also reviews the epidemiology of this disease and the currently available diagnostic laboratory tests and recommended treatment options.

African tick bite fever is the most commonly encountered travel-associated rickettsiosis, occurring in as many as 5% of travelers returning from rural subequatorial Africa. This case report illustrates that rifampin represents an effective alternative to doxycycline for treatment of African tick bite fever in some selective situations.