Molecular evidence and phylogenetic delineation of spotted fever group Rickettsia species in Amblyomma ticks from cattle in Gauteng and Limpopo Provinces, South Africa

Abstract

Objective: To determine the prevalence of tick-borne pathogens with a particular focus on Rickettsia spp. in ticks collected from cattle in Gauteng and Limpopo Provinces, South Africa. Methods: A total of 200 ticks were collected from cattle within the Madala livestock, Pretoria, Gauteng Province and in Mankweng Township, Polokwane, Limpopo Province in 2019. The ticks were morphologically identified and processed individually for a total genomic DNA extraction. Specific primers targetting ompA, ompB, and the 17KDa genes were used for a molecular screening and delineation of Rickettsia from the extracted genetic materials using polymerase chain reaction (PCR) technique. PCR amplicons of positive samples were sequenced bidirectionally using the Sanger sequencing method. Sequences generated were processed and analysed using appropriate bioinformatics software. Results: The ticks were morphologically identified as Amblyomma spp. PCR profiling of the genomic DNA samples revealed the presence of the Rickettsia pathogen in 42 (21%) of the ticks collected from both Provinces. Out of the genes profiled, 14 (7%) were positive for 17KDa, 42 (21%) for ompA and 32 (16%) were positive for ompB genes respectively. The nucleotide blast of the sequenced genomes showed high similarity, as high as 100% with other reference Rickettsia (R.) africae in the GenBank. The phylogenetic analysis of the sequences further validated them as R. africae with their characteristic clustering pattern with related reference sequences. Conclusions: There is an abundance of R. africae in Amblyomma ticks collected from cattle in the study areas. This has serious public health implications as individuals who accidentally get infested with the ticks could acquire R. africae. Hence, adequate precautions in terms of sensitization of farmers about the risk and mass mobilization drive to control the vectors in the areas are highly recommended to safeguard public health.