Role of Sca2 and RickA in the dissemination of Rickettsia parkeri in Amblyomma maculatum

Emma K. Harris, Krit Jirakanwisal, Victoria I. Verhoeve, Chanida Fongsaran, Chanakan Suwanbongkot, Matthew D. Welch, Kevin R. Macaluso

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


The Gram-negative obligate intracellular bacterium Rickettsia parkeri is an emerging tick-borne human pathogen. Recently, R. parkeri Sca2 and RickA have been implicated in adherence and actin-based motility in vertebrate host cell infection models; however, the rickettsia-derived factors essential to tick infection are unknown. Using R. parkeri mutants lacking functional Sca2 or RickA to compare actin polymerization, replication, and cell-to-cell spread in vitro, similar phenotypes in tick and mammalian cells were observed. Specifically, actin polymerization in cultured tick cells is controlled by the two separate proteins in a time-dependent manner. To assess the role of Sca2 and RickA in dissemination in the tick host, Rickettsia-free Amblyomma maculatum, the natural vector of R. parkeri, was exposed to wild-type, R. parkeri rickA::tn, or R. parkeri sca2::tn bacteria, and individual tick tissues, including salivary glands, midguts, ovaries, and hemolymph, were analyzed at 12 h and after continued bloodmeal acquisition for 3 or 7 days postexposure. Initially, ticks exposed to wild-type R. parkeri had the highest rickettsial load across all organs; however, rickettsial loads decreased and wild-type rickettsiae were cleared from the ovaries at 7 days postexposure. In contrast, ticks exposed to R. parkeri rickA::tn or R. parkeri sca2::tn had comparatively lower rickettsial loads, but bacteria persisted in all organs for 7 days. These data suggest that while RickA and Sca2 function in actin polymerization in tick cells, the absence of these proteins did not change dissemination patterns within the tick vector.

Original languageEnglish (US)
Article numbere00123-18
JournalInfection and immunity
Issue number6
StatePublished - Jun 1 2018
Externally publishedYes


  • Actin-based motility
  • Amblyomma maculatum
  • RickA
  • Rickettsia parkeri
  • Sca2

ASJC Scopus subject areas

  • Parasitology
  • Microbiology
  • Immunology
  • Infectious Diseases


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