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Open Access Research

Experimental infection of cotton rats and bobwhite quail with Rickettsia parkeri

Gail Miriam Moraru1, Jerome Goddard2, Christopher D Paddock3 and Andrea Varela-Stokes1*

Author Affiliations

1 Department of Basic Sciences, College of Veterinary Medicine, Mississippi State University, Wise Center, Spring Street, Mississippi State, MS, 39762, USA

2 Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University, Mississippi State, MS, USA

3 Infectious Diseases Pathology Branch, Centers for Disease Control and Prevention, Atlanta, GA, USA

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Parasites & Vectors 2013, 6:70  doi:10.1186/1756-3305-6-70

Published: 15 March 2013

Abstract

Background

Amblyomma maculatum is the primary vector for Rickettsia parkeri, a spotted fever group rickettsia (SFGR) and human pathogen. Cotton rats and quail are known hosts for larval and nymphal A. maculatum; however, the role of these hosts in the ecology of R. parkeri is unknown.

Methods

Cotton rats and quail were inoculated with low or high doses of R. parkeri (strain Portsmouth) grown in Vero cells to evaluate infection by R. parkeri in these two hosts species. Animals were euthanized 2, 4, 7, 10, and 14 days post-injection (dpi) and blood, skin, and spleen samples were collected to analyze by Vero cell culture and polymerase chain reaction (PCR). In a second trial, cotton rats and quail were inoculated with R. parkeri and nymphal A. maculatum ticks were allowed to feed on animals. Animals were euthanized on 14, 20, 28, 31, and 38 dpi and blood and tissues were collected for serology and PCR assays. Fed ticks were tested for R. parkeri by PCR and Vero cell culture.

Results

Rickettsia parkeri was isolated in cell culture and detected by PCR in skin, blood, and spleen tissues of cotton rats in the initial trial 2, 4, and 7 dpi, but not in quail tissues. In the second trial, no ticks tested positive for R. parkeri by PCR or cell culture.

Conclusions

These studies demonstrate that viable R. parkeri rickettsiae can persist in the tissues of cotton rats for at least 7 days following subcutaneous inoculation of these bacteria; however, quail are apparently resistant to infection. Rickettsia parkeri was not detected in nymphal ticks that fed on R. parkeri-inoculated cotton rats or quail, suggesting an alternate route of transmission to naïve ticks.

Keywords:
Rickettsia parkeri; Experimental infection; Cotton rat; Quail