Isolation ofRickettsia parkeriand Identification of a Novel Spotted Fever GroupRickettsiasp. from Gulf Coast Ticks (Amblyomma maculatum) in the United States

Abstract

Until recently, Amblyomma maculatum (the Gulf Coast tick) had garnered little attention compared to other species of human-biting ticks in the United States. A. maculatum is now recognized as the principal vector of Rickettsia parkeri, a pathogenic spotted fever group rickettsia (SFGR) that causes an escharassociated illness in humans that resembles Rocky Mountain spotted fever. A novel SFGR, distinct from other recognized Rickettsia spp., has also been detected recently in A. maculatum specimens collected in several regions of the southeastern United States. In this study, 198 questing adult Gulf Coast ticks were collected at 4 locations in Florida and Mississippi; 28% of these ticks were infected with R. parkeri, and 2% of these were infected with a novel SFGR. Seventeen isolates of R. parkeri from individual specimens of A. maculatum were cultivated in Vero E6 cells; however, all attempts to isolate the novel SFGR were unsuccessful. Partial genetic characterization of the novel SFGR revealed identity with several recently described, incompletely characterized, and noncultivated SFGR, including "Candidatus Rickettsia andeanae" and Rickettsia sp. Argentina detected in several species of Neotropical ticks from Argentina and Peru. These findings suggest that each of these "novel" rickettsiae represent the same species. This study considerably expanded the number of low-passage, A. maculatum-derived isolates of R. parkeri and characterized a second, sympatric Rickettsia sp. found in Gulf Coast ticks.

Detection ofRickettsia parkerifrom within Piura, Peru, and the First Reported Presence ofCandidatusRickettsia andeanae in the TickRhipicephalus sanguineus

“…We now report the presence of R. parkeri in Peru. R. parkeri is commonly found in A. maculatum ticks in the southeastern United States (Paddock et al 2010, Varela-Stokes et al 2011, but an infected A. maculatum had not been documented in Peru until now. Two specimens of A. maculatum were detected with co-infections of Candidatus R. andeanae and R. parkeri, a mixed infection of the same tick with 2 species of Rickettsia that is not frequently reported in the literature.…”

Update on Tick-Borne Rickettsioses around the World: a Geographic Approach

“…"Candidatus Rickettsia andeanae" was first documented in North America in 2010 in A. maculatum ticks collected in Florida and Mississippi (96). Since then, this SFG rickettsia has been identified throughout the U.S. range of A. maculatum ticks, occurring sympatrically with but typically at frequencies considerably lower than those of R. parkeri (98)(99)(100)(101)143).…”

“…The first confirmed human infection with R. parkeri was reported in 2004, and approximately 15 cases of R. parkeri rickettsiosis have been described in the literature since that initial report (66)(67)(68)(69)(70). In the United States, Amblyomma maculatum (the Gulf Coast tick) is the principal vector for these bacteria, and R. parkeri is detected in 8% to 43% of questing adult A. maculatum ticks collected in states along the Gulf Coast and the southern Atlantic region (95)(96)(97)(98)(99)(100)(101). R. parkeri is distributed throughout multiple tissues of infected A. maculatum ticks, including the salivary glands, the midgut, the Malpighian tubules, and the ovaries (102).…”

Susceptibility of Inbred Mice to Rickettsia parkeri

“…The contributing factors responsible for the variation in disease manifestation among SFG species are currently unknown. The recognition of R. parkeri has increased since the first confirmed human case of disease reported in 2004 (15), with more than 20 cases emerging around the southeastern United States (13,14,25). The sympatric distribution of pathogenic SFG Rickettsia in the United States (Western Hemisphere) warrants the differentiation of these infections to better comprehend the epidemiological landscape of TBRDs.…”