Feeding byAmblyomma maculatum(Acari: Ixodidae) EnhancesRickettsia parkeri(Rickettsiales: Rickettsiaceae) Infection in the Skin

Abstract

Rickettsia parkeri Luckman (Rickettsiales: Rickettsiaceae), a member of the spotted fever group of Rickettsia, is the tick-borne causative agent of a newly recognized, eschar-associated rickettsiosis. Because of its relatively recent designation as a pathogen, few studies have examined the pathogenesis of transmission of R. parkeri to the vertebrate host. To further elucidate the role of tick feeding in rickettsial infection of vertebrates, nymphal Amblyomma maculatum Koch (Acari: Ixodidae) were fed on C3H/HeJ mice intradermally inoculated with R. parkeri (Portsmouth strain). The ticks were allowed to feed to repletion, at which time samples were taken for histopathology, immunohistochemistry (IHC), quantitative polymerase chain reaction (qPCR) for rickettsial quantification, and reverse transcriptase polymerase chain reaction(RT-PCR)for expression of Itgax, Mcp1, and Il1β. The group of mice that received intradermal inoculation of R. parkeri with tick feeding displayed significant increases in rickettsial load and IHC staining, but not in cytokine expression, when compared with the group of mice that received intradermal inoculation of R. parkeri without tick feeding. Tick feeding alone was associated with histopathologic changes in the skin, but these changes, and particularly vascular pathology, were more pronounced in the skin of mice inoculated previously with R. parkeri and followed by tick feeding. The marked differences in IHC staining and qPCR for the R. parkeri with tick feeding group strongly suggest an important role for tick feeding in the early establishment of rickettsial infection in the skin.

Effect ofAmblyomma maculatum(Acari: Ixodidae) Saliva on the Acute Cutaneous Immune Response toRickettsia parkeriInfection in a Murine Model

“…This result is in contrast to a previous study which documented that tick feeding plus R. parkeri inoculation resulted in increased rickettsial load in the late stages of infection as compared to R. parkeri inoculation alone (Grasperge et al 2014). There are several potential reasons for this difference of results.…”

“…A colony of Rickettsia -free A. maculatum were acquired from BEI resources and maintained on rodents as previously described (Troughton and Levin 2007, Grasperge et al 2014, Banajee et al 2015). Animal care and use for tick rearing purposes was approved by the LSU Institutional Animal Care and Use Committee (IACUC; Protocol Number: 13-034).…”

“…The rickettsiae were resuspended in sucrose–phosphate–glutamic acid buffer (SPG; Feng et al 2004) to obtain the desired inoculation dose of 5.5 × 10 6 live rickettsiae/25 µl. Since the amount of R. parkeri inoculated by ticks during natural feeding is unknown, this dose was chosen based on the fact that it is within the range reported in wild-caught ticks (Monje et al 2014), and similar to the dose used with other animal models of SFG rickettsiosis (Feng et al 1993, Bechah et al 2007, Grasperge et al 2012, Grasperge et al 2014, Banajee et al 2015). The same volume of uninfected Vero cell culture was prepared in SPG as above with the exception of bacterial inoculation and counting.…”

“…Furthermore, while it has been shown that tick feeding at the rickettsial inoculation site enhances rickettsial disease in murine and primate models and rickettsial proliferation in the mouse model (Grasperge et al 2014, Banajee et al 2015), the effect of the tick saliva on the cutaneous immune response to rickettsial infection has not been quantified. Therefore, the aim of this study was to evaluate the acute murine cutaneous immune response to R. parkeri with and without the influence of A. maculatum saliva as compared to saliva inoculation alone and untouched controls.…”

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

“…R. andeanae” elicits infection or disease in humans or animals. It has been suggested that other putative rickettsial symbionts, including Rickettsia amblyommii and Rickettsia montanensis cause abortive, transient, or subclinical infections in humans, dogs, and other animals (Apperson et al, 2008, Zanetti et al, 2008, McQuiston et al, 2012, Grasperge et al, 2014 and Barrett et al, 2014). …”