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Updated: Aug 14, 2026
Feeding of Ticks on Animals for Transmission and Xenodiagnosis in Lyme Disease Research
Published on: August 31, 2013
Amblyomma maculatum Feeding Augments Rickettsia parkeri Infection in a Rhesus Macaque Model: A Pilot Study
Kaikhushroo H Banajee1, Monica E Embers2, Ingeborg M Langohr3
1Vector-borne Disease Laboratories, Department of Pathobiological Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, Louisiana, 70803, United States of America.
Abstract:
Rickettsia parkeri is an emerging eschar-causing human pathogen in the spotted fever group of Rickettsia and is transmitted by the Gulf coast tick, Amblyomma maculatum. Tick saliva has been shown to alter both the cellular and humoral components of the innate and adaptive immune systems. However, the effect of this immunomodulation on Rickettsia transmission and pathology in an immunocompetent vertebrate host has not been fully examined. We hypothesize that, by modifying the host immune response, tick feeding enhances infection and pathology of pathogenic spotted fever group Rickettsia sp. In order to assess this interaction in vivo, a pilot study was conducted using five rhesus macaques that were divided into three groups. One group was intradermally inoculated with low passage R. parkeri (Portsmouth strain) alone (n = 2) and another group was inoculated during infestation by adult, R. parkeri-free A. maculatum (n = 2). The final macaque was infested with ticks alone (tick feeding control group). Blood, lymph node and skin biopsies were collected at several time points post-inoculation/infestation to assess pathology and quantify rickettsial DNA. As opposed to the tick-only animal, all Rickettsia-inoculated macaques developed inflammatory leukograms, elevated C-reactive protein concentrations, and elevated TH1 (interferon-γ, interleukin-15) and acute phase inflammatory cytokines (interleukin-6) post-inoculation, with greater neutrophilia and interleukin-6 concentrations in the tick plus R. parkeri group. While eschars formed at all R. parkeri inoculation sites, larger and slower healing eschars were observed in the tick feeding plus R. parkeri group. Furthermore, dissemination of R. parkeri to draining lymph nodes early in infection and increased persistence at the inoculation site were observed in the tick plus R. parkeri group. This study indicates that rhesus macaques can be used to model R. parkeri rickettsiosis, and suggests that immunomodulatory factors introduced during tick feeding may enhance the pathogenicity of spotted fever group Rickettsia.
Insights
Tick feeding enhances Rickettsia parkeri infection and pathology in rhesus macaques. Immunomodulatory factors from tick saliva may increase disease severity and pathogen persistence.
Area of Science:
- Infectious Diseases
- Immunology
- Veterinary Medicine
Background:
- Rickettsia parkeri causes eschars and is transmitted by Amblyomma maculatum ticks.
- Tick saliva can modulate host immune responses, but its effect on Rickettsia pathogenesis is unclear.
Purpose of the Study:
- To investigate how tick feeding influences Rickettsia parkeri infection and pathology in a vertebrate host.
- To assess the role of tick immunomodulation in enhancing spotted fever group rickettsiosis.
Main Methods:
- A pilot study used five rhesus macaques divided into three groups: R. parkeri inoculation alone, R. parkeri inoculation during tick infestation, and tick infestation alone.
- Collected blood, lymph node, and skin biopsies to assess pathology and quantify rickettsial DNA.
- Monitored clinical signs, inflammatory markers (C-reactive protein, cytokines), and lesion development.
Main Results:
- All R. parkeri-inoculated macaques showed inflammatory responses; the tick plus R. parkeri group had higher neutrophilia and IL-6.
- Larger, slower-healing eschars formed in the tick plus R. parkeri group.
- R. parkeri disseminated earlier to lymph nodes and persisted longer at the inoculation site in the tick plus R. parkeri group.
Conclusions:
- Rhesus macaques serve as a suitable model for R. parkeri rickettsiosis.
- Tick feeding, through immunomodulatory saliva, appears to enhance the pathogenicity of R. parkeri.
- Understanding tick-host-pathogen interactions is crucial for managing spotted fever group rickettsioses.
