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Surveillance for Metastriate Ticks and Spotted Fever Group Rickettsioses in Southern Illinois

Victoria Phillips1, J Matthew Flenniken2, Levi Mick1

  • 1Illinois Natural History Survey, Prairie Research Institute, University of Illinois Urbana-Champaign, Champaign, Illinois, USA.

The American Journal of Tropical Medicine and Hygiene
|June 18, 2026
PubMed

Insights

Spotted fever group rickettsioses (SFGR) are increasing in Illinois. This study found new Rickettsia species in ticks, including Amblyomma maculatum, and linked A. americanum to higher SFGR rates.

Area of Science:

  • Veterinary Entomology
  • Infectious Diseases
  • Molecular Biology

Background:

  • Spotted fever group rickettsioses (SFGR) represent a growing public health concern in the U.S.
  • Geographical expansion of tick vectors like Amblyomma americanum and Amblyomma maculatum necessitates understanding Rickettsia species prevalence in new areas.
  • Amblyomma maculatum is a significant vector for Rickettsia parkeri.

Purpose of the Study:

  • To investigate the prevalence of Rickettsia species in ticks from southern Illinois, a region with rising SFGR cases.
  • To assess the role of expanding tick populations, particularly Amblyomma maculatum, in SFGR transmission dynamics.
  • To identify Rickettsia species in Amblyomma maculatum, Amblyomma americanum, and Dermacentor variabilis ticks.

Main Methods:

  • Tick collection across 16 counties in southern Illinois.
  • Real-time polymerase chain reaction (PCR) for R. amblyommatis, R. parkeri, and R. rickettsii detection.
  • Sequencing of the gltA gene for comprehensive Rickettsia species identification.

Main Results:

  • Amblyomma maculatum was detected in more counties than previously reported, with significant prevalence of R. parkeri (16.4%) and Candidatus R. andeanae (28.7%).
  • Rickettsia montanensis and R. bellii were identified in Dermacentor variabilis.
  • Amblyomma americanum showed high R. amblyommatis prevalence (48.5% adults, 48.4% nymphs), correlating positively with SFGR incidence.

Conclusions:

  • The expansion of Amblyomma maculatum introduces R. parkeri and Candidatus R. andeanae to southern Illinois, diversifying SFGR agents.
  • Amblyomma americanum appears to be a primary driver of current SFGR incidence in the region.
  • Continued surveillance is vital to monitor the impact of A. maculatum expansion and evolving Rickettsia spp. transmission patterns.

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