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.

Knowledge, attitudes and practices on African tick bite fever of rural livestock communities living in a livestock-wildlife interface area in the Eastern Cape Province of South Africa

Background African tick bite fever (ATBF) caused by Rickettsia africae and transmitted by Amblyomma spp. ticks is one of the zoonotic tick-borne fevers from the spotted fever group (SFG) of rickettsiae, which is an emerging global health concern. There is paucity of information regarding the occurrence and awareness of the disease in endemic rural livestock farming communities living in livestock-wildlife interface areas in South Africa. Methods The purpose of the study was to assess the level of knowledge, attitudes and practices on ticks and ATBF infection from a community living in livestock-wildlife interface areas in South Africa. A focus group discussion (FGD) was carried out followed by verbal administration of a standardized semi-structured questionnaire a month later to 38 rural livestock farmers (23 from Caquba area and 15 from Lucingweni area where A. hebraeum was absent). An FGD was conducted in Caquba (situated at the livestock-wildlife interface where Amblyomma hebraeum was prevalent on cattle and infected with Rickettsia africae) in the O.R. Tambo district of the Eastern Cape province of South Africa. Results Results from the FGD and questionnaire survey showed that participants from the two rural communities were not aware of ATBF and were not aware that ticks are vectors of the disease. Respondents from Caquba reported of having frequent exposure to tick bites (91.3%, 21/23) specifically from the anthropophilic A. hebrauem which they were able to identify as Qwelagqibe in IsiXhosa (their vernacular). Thirteen out of 15 (86.7%) of respondents from Lucingweni reported that they had never been bitten by ticks, which corresponded with the absence of A. hebraeum from their locality as evidenced from results of a concurrent study on prevalence of ticks on livestock in the area. Both communities confirmed to being “very concerned” of tick bites and we presume this was more related to the localized wounds from the bites than to the diseases transmitted by the ticks. Conclusions We recommend future studies encompassing seroprevalence of ATBF in Caquba and other communities at risk in South Africa including establishing surveillance systems to monitor the seasonal infection rates in ticks, cattle and humans.

Rickettsia africae an Agent of African Tick Bite Fever in Ticks Collected from Domestic Animals in Eastern Cape, South Africa

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.

Amblyomma hebraeum is the predominant tick species on goats in the Mnisi Community Area of Mpumalanga Province South Africa and is co-infected with Ehrlichia ruminantium and Rickettsia africae

Background: In sub-Saharan Africa, ticks of the genus Amblyomma are vectors of heartwater disease in domestic ruminants, caused by the rickettsial pathogen Ehrlichia ruminantium. Immature stages of these ticks often bite humans, whereby they act as vectors of tick-bite fever caused by Rickettsia africae. Moreover, Amblyomma ticks cause considerable damage to livestock due to their feeding behaviour. In South Africa, we studied the relative abundance of Amblyomma hebraeum ticks on goats of emerging farmers in Mpumalanga Province. A selected number of A. hebraeum nymphs and adult ticks was tested for co-infection with E. ruminantium and R. africae. Methods: A total of 630 indigenous goats, belonging to farmers in the Mnisi Community area, were examined for ticks in 2013 and 2014. All ticks were identified, and a selected number was tested by PCR with reverse line blot hybridisation (RLB).Results: In total, 13,129 ticks were collected from goats distributed over 17 different households. Amblyomma hebraeum was the predominant species collected, followed by Rhipicephalus microplus. Small numbers of Rhipicephalus appendiculatus, Rhipicephalus simus and Rhipicephalus zambeziensis were also identified. A. hebraeum was present throughout the year, with peak activity of adults in summer (November) and nymphs in winter (July). The ratio between adults and nymphs ranged from 1:2.7 in summer to 1:55.1 in winter. The mean prevalence of infection for E. ruminantium by PCR/RLB in adult ticks was 17.4% (31/178), whereas 15.7% (28/178) were infected with R. africae. In nymphs, 28.4% were infected with E. ruminantium and 38.8% carried R. africae infection. Co-infections of E. ruminantium and R. africae in adult and nymphal ticks were 3.9% (7/178) and 10% (14.9), respectively. Lameness of goats due to predilection of ticks for the interdigital space of their feet was observed in 89% of the households.Conclusions: Goats act as important alternative hosts for cattle ticks, which underscored the necessity to include goats in tick control programs. It is suggested to use acaricide-impregnated leg-bands as a sustainable method to kill ticks and prevent lameness in goats. The continuous challenge of goats by considerable numbers of E. ruminantium- infected ticks is a major obstacle for upgrading the indigenous goat breeds. Humans appear to be at risk to contract tick-bite fever in this area.