Deciphering the Constituents of Vector Competence

Ticks act as vectors for an array of rickettsial species; however, field and laboratory studies suggest transmission of bacteria occurs with specificity between tick and rickettsial species. To better understand the infection potential between several tick and rickettsial species, two sympatric species of ticks, D. variabilis and A. maculatum, were exposed to the rickettsial pathogens Rickettsia rickettsii and Rickettsia parkeri; non-pathogenic Rickettsia montanensis and Rickettsia amblyommii; or, flea-borne Rickettsia felis Adult, female D. variabilis and A. maculatum were capillary fed with either Rickettsia or delivery control. Fitness-related metrics such as engorgement weight, egg production index, and hatch percentage were then assessed. Subsamples of egg clutches for each treatment group were assessed for transovarial transmission (TOT) of rickettsiae by qPCR. Subsequently, transstadial transmission (TST) was assessed in the F₁ progeny. Results show that D. variabilis were more susceptible to infection, and Amblyomma-associated Rickettsia were most commonly maintained via TST. Towards understanding the molecular mechanisms governing tick infection, studies have focused on identifying the tick immune factors that may influence the infection process.  Examining the biological and molecular characteristics of rickettsial infection in ticks will lead to a better understanding of the eco-epidemiology of Rickettsia and rickettsial diseases.