Prevalence of tick-borne pathogens in Rhipicephalus species infesting domestic animals in Africa: A systematic review and meta-analysis.

Rhipicephalus ticks transmit important tick-borne pathogens (TBPs) such as Anaplasma, Babesia, and Theileria spp. which cause major economic losses in livestock production and contribute to emerging zoonotic diseases. A vast amount of data is available based on the demonstration of these pathogens in various host tissues, with limited information on the prevalence of these TBPs and their vectors. Quantifying TBPs infection rates among Rhipicephalus spp. is essential for the effective control and management of TBDs in domestic animals and surveillance of emerging diseases in humans, as they have close social associations. This review summarizes the prevalence of TBPs in Rhipicephalus spp. from domestic animals of Africa. A thorough search was done in SCOPUS, Web of Knowledge, PubMed, Google Scholar, and library sources from 2000 to 2022. All research in Africa reporting TBPs infection rates in Rhipicephalus spp. were included in the selection criteria. The meta-analysis evaluated publication bias using funnel plots to analyze the observed heterogeneity and applied a quality effects model. Prevalence estimates were based on data from 46 studies reporting TBPs infection rates in Rhipicephalus spp. from northern and sub-Saharan Africa. Sub-group analysis was done by geographic region and tick genus. A total of 12,368 Rhipicephalus spp. collected from domestic animals in Africa were used in the meta-analysis. The quality effects model revealed a high degree of heterogeneity among studies on the various TBPs. The overall prevalence of detected TBPs such as Theileria spp. was 8% (95% CI: 3-15%), Rickettsia spp. 3% (95% CI: 0-9%), Ehrlichia spp. 7% (95% CI: 2-14%), Anaplasma spp. 8% (95% CI: 2-16%), Coxiella spp. 10% (95% CI: 1-26%) and Babesia spp. 6% (95% CI: 2-12%). Northern Africa had the highest prevalence of Anaplasma spp. 12% (95% CI: 3-25%) and Theileria spp. 16% (95% CI: 0-42%). Whilst West Africa had the highest prevalence for Ehrlichia spp. 12% (95% CI: 3-24%) and eastern Africa for Rickettsia spp. 8% (95% CI: 4-12%). This is a systematic and quantitative investigation of the various TBPs detected in Rhipicephalus tick vectors from domestic animal hosts in Africa. The findings demonstrate considerable species variation across the African continent and offer preliminary estimates of infection rates for the continent.

Low genetic diversity and population structuring of Amblyomma hebraeum and Rickettsia africae from coastal and inland regions in the Eastern Cape Province of South Africa.

Amblyomma hebraeum is the main vector of Rickettsia africae, the causative agent of African tick bite fever in southern Africa. Because pathogen dispersal is known to be influenced by tick adaptations to climate or host species, this study aimed to analyse the genetic diversity of A. hebraeum and R. africae infection of ticks collected from cattle in the Eastern Cape province of South Africa. DNA was extracted, amplified, and sequenced for the COI and ITS2 markers from A. hebraeum samples and the 17 kDa and ompA genes for rickettsial detection. Between six and ten haplotypes were identified from 40 COI and 31 ITS2 sequences; however, no population structuring was observed among sites (ΦST = 0.22, p < 0.05). All A. hebraeum isolates clustered with southern Africa GenBank isolates. Rickettsia africae was detected in 46.92% (95% CI = 41%-53%, n = 260) of ticks. All R. africae isolates clustered with strain PELE and Chucks, which were reported previously from South Africa. These results confirm that A. hebraeum populations are undergoing a recent population expansion driven by cattle movement, facilitating local and long dispersal events across the Eastern Cape province.

Prevalence of Rickettsia africae in tick vectors collected from mammalian hosts in sub-Saharan Africa: A systematic review and meta-analysis.

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.

Genetic diversity of Rickettsia africae isolates from Amblyomma hebraeum and blood from cattle in the Eastern Cape province of South Africa.

Rickettsia africae is a re-emerging tick-borne pathogen causing African tick bite fever (ATBF) in humans. Amblyomma variegatum is the principal vector in most sub-Sahara African countries, whereas in South Africa it is A. hebraeum. Reports of high genetic heterogeneity among R. africae isolates in southern Africa have prompted the need for molecular investigations of isolates form South Africa. Therefore, this study aimed to determine the prevalence and genetic diversity of R. africae in A. hebraeum collected from cattle, grazing pasture, as well as from blood of cattle in the Eastern Cape Province of South Africa. Amblyomma hebraeum and blood from cattle were screened by PCR and the gltA, ompA, ompB, sca4, and 17kDa genes were sequenced for R. africae from samples collected from Caquba in Port St. Johns along the coastal region in the Eastern Cape province of South Africa. The overall proportion of adult A. hebraeum that were positive for the gltA and ompA genes was 0.63 (108/180). The overall proportion of nymphs positive for the gltA and ompA genes was 0.62 (23/37) and 0.22 (20/90) from cattle blood. A positive R. africae infection was inferred by analysis of 26 sequences of the ompA, gltA, ompB, 17kDa and sca4 genes. Neighbour-joining and Maximum Likelihood analysis revealed that the study isolates were closely related to R. africae isolates from South Africa deposited in GenBank, forming a clade that was separate from north, east and west African strains. This study provides new information on the epidemiology and phylogeny of R. africae isolated from A. hebraeum ticks in the Eastern Cape province of South Africa. The heterogeneity observed between R. africae isolates from South Africa deposited in GenBank and R. africae isolates from Africa retrieved from Genbank highlight the importance of differentiation and tracking of the genetic movement among R. africae isolates in southern Africa for the better characterisation of ATBF cases, especially in rural communities and travellers visiting the region.