High prevalence of "Candidatus Rickettsia andeanae" and apparent exclusion of Rickettsia parkeri in adult Amblyomma maculatum (Acari: Ixodidae) from Kansas and Oklahoma

Abstract

Amblyomma maculatum (the Gulf Coast tick), an aggressive, human-biting, Nearctic and Neotropical tick, is the principal vector of Rickettsia parkeri in the United States. This pathogenic spotted fever group Rickettsia species has been identified in 8-52% of questing adult Gulf Coast ticks in the southeastern United States. To our knowledge, R. parkeri has not been reported previously from adult specimens of A. maculatum collected in Kansas or Oklahoma. A total of 216 adult A. maculatum ticks were collected from 18 counties in Kansas and Oklahoma during 2011-2014 and evaluated by molecular methods for evidence of infection with R. parkeri. No infections with this agent were identified; however, 47% of 94 ticks collected from Kansas and 73% of 122 ticks from Oklahoma were infected with "Candidatus Rickettsia andeanae" a spotted fever group Rickettsia species of undetermined pathogenicity. These preliminary data suggest that "Ca. R. andeanae" is well-adapted to survival in populations of A. maculatum in Kansas and Oklahoma, and that its ubiquity in Gulf Coast ticks in these states may effectively exclude R. parkeri from their shared arthropod host, which could diminish markedly or preclude entirely the occurrence of R. parkeri rickettsiosis in this region of the United States.

Keywords: Amblyomma maculatum; Rickettsia parkeri; Rickettsial interference; “Candidatus Rickettsia andeanae”.

Fig. 1

Frequency of infection with “Candidatus Rickettsia andeanae” among 216 questing adult Amblyomma maculatum ticks collected from Kansas (Anderson, Butler, Crawford, Geary, Morris, Neosho, Osage, Riley, and Shawnee counties) and Oklahoma (Cleveland, Cotton, Kiowa, Lincoln, Osage, Payne, Tillman, Tulsa, and Washington counties) during 2011–2014. Fractions represent the numbers of ticks infected with “Ca. R. andeanae” over the number of ticks that were evaluated by the real-time PCR assay. No molecular evidence of infection with Rickettsia parkeri was identified in any specimen of A. maculatum in either state.