Amblyomma maculatum-associated rickettsiae in vector tissues and vertebrate hosts during tick feeding.

Rickettsia parkeri, a causative agent of spotted fever rickettsiosis, is transmitted by Amblyomma maculatum (Gulf Coast tick), a tick that may also carry a non-pathogenic spotted fever group Rickettsia, "Candidatus Rickettsia andeanae". Here, we evaluated R. parkeri and "Candidatus R. andeanae" in tissues from A. maculatum prior to, during, and after blood feeding on rabbits. Using colony-reared A. maculatum that were capillary-fed uninfected cells, R. parkeri, "Candidatus R. andeanae", or both rickettsiae, we detected higher levels of Rickettsia spp. in the respective treatment groups. Rickettsial levels increased during blood feeding for both R. parkeri and "Candidatus R. andeanae", with a greater increase in R. parkeri in co-infected ticks compared to singly-infected ticks. We detected transovarial transmission of "Candidatus R. andeanae" in egg and larval cohorts and confirmed vertical transmission of R. parkeri in one group of larvae. Rabbits from all Rickettsia-exposed groups seroconverted on immunofluorescent antibody testing using R. parkeri antigen. Visualization of "Candidatus R. andeanae" in tick salivary glands suggested potential transmission via tick feeding. Here, rickettsial levels in artificially infected ticks demonstrate changes during feeding and transovarial transmission that may be relevant for interpreting rickettsial levels detected in wild A. maculatum.