Detection of a Spotted Fever Group Rickettsia in Amblyomma cajennense (Acari: Ixodidae) in South Texas

Adrian N. Billings, Xue Jie Yu, Pete D. Teel, David H. Walker

Research output: Contribution to journalArticle

39 Scopus citations


Thai tick typhus rickettsia (strain TT-118), a spotted fever group rickettsia of indeterminant pathogenicity, was isolated from a mixed pool of larval Ixodes and Rhipicephalus ticks collected from Thailand in 1962. Here we report the surprising finding of a spotted fever group rickettsia with closest sequence homology to the Thai tick typhus rickettsia in Amblyomma cajennense (F.) ticks from south Texas. Sequence analysis was performed on segments of 3 genes that differentiate rickettsial species; all 3 genes sequenced, the 17-kDa, glta, and rompA, when compared with those of other rickettsiae, showed the highest degree of similarity to the Thai tick typhus rickettsia with 99.5, 99.5, and 100% homology, respectively. This is the 1st finding of a rickettsial species in A. cajennense ticks in Texas and the United States. If this rickettsia is pathogenic, exposure to infected A. cajennense ticks may pose a previously unrecognized health risk to people who have been fed upon by these ticks.

Original languageEnglish (US)
Pages (from-to)474-478
Number of pages5
JournalJournal of medical entomology
Issue number4
StatePublished - Jul 1998



  • Amblyomma cajennense
  • Rickettsial 17-kDa protein gene
  • Rickettsial citrate synthase gene
  • Rickettsial outer membrane protein A gene
  • Spotted fever group rickettsia
  • Tick

ASJC Scopus subject areas

  • Parasitology
  • veterinary(all)
  • Insect Science
  • Infectious Diseases

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