Elisha Chatanga, Wessam Mohamed Ahmed Mohamed, Samuel Kelava, Naoki Hayashi, Yuma Ohari, Mohamed Abdallah Mohamed Moustafa, J.W. Magona, Kyoko Hayashida, Yongjin Qiu, Nariaki Nonaka, Ryo Nakao
BACKGROUND: The tropical bont tick Amblyomma variegatum, which is widespread in Africa and the Caribbean islands, is of both medical and veterinary importance as the principal vector of intracellular bacterial pathogens Ehrlichia ruminantium, causing heartwater in animals, and Rickettsia africae, causing African tick bite fever (ATBF) in humans. This tick species is highly invasive and has been reported to expand its geographical distribution as well as host range. Rickettsia africae is also recognized as a common endosymbiont in A. variegatum, but its transmission dynamics within this tick population remain poorly understood. METHODOLOGY: To investigate the co-phylogenetic patterns between A. variegatum and R. africae, we sequenced the complete mitogenomes of A. variegatum and performed multi-locus sequence typing (MLST) of six housekeeping genes of R. africae. The resulting sequence data were used to examine the hypothesis that R. africae is predominantly transmitted vertically within A. variegatum populations, which would lead to congruent phylogenies between vector and pathogen. RESULTS: There was geographical population sub-structuring in the mitogenomes of A. variegatum. The prevalence of R. africae in the examined ticks was 100%. The tanglegram showed non-strict co-cladogenesis between A. variegatum and R. africae. Furthermore, the Procrustes Application to Cophylogenetic (PACo) analysis and residuals of vector-pathogen associations showed no statistically significant association between A. variegatum and R. africae genotypes. CONCLUSIONS: This study was the first to examine the spread of pathogenic/endosymbiotic bacterium R. africae in the A. variegatum populations using a mitogenomic approach. The results support both vertical and horizontal transmission of R. africae within A. variegatum. These findings also highlight the potential of R. africae to adapt to multiple animal species, which may complicate efforts to control it as a human pathogen.