Detection and Identification of Spotted Fever Group Rickettsiae in Dermacentor Species from Southern California

National Center for Zoonotic, Vector-borne and Enteric Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA 30333, USA.
Journal of Medical Entomology (Impact Factor: 1.95). 06/2008; 45(3):509-16. DOI: 10.1603/0022-2585(2008)45[509:DAIOSF]2.0.CO;2
Source: PubMed


Dermacentor occidentalis Marx and Dermacentor variabilis (Say) commonly bite humans in California. These Dermacentor species may play a role in transmitting spotted fever group (SFG) rickettsiae to humans in many parts of the state where Dermacentor andersoni Stiles, a known vector for the etiologic agent of Rocky Mountain spotted fever, Rickettsia rickettsii, is absent. However, the specific rickettsial agents present in these ticks and their current prevalence are poorly understood. In total, 365 D. occidentalis and 10 D. variabilis were collected by flagging vegetation at 16 sites in five counties of southern California. The presence of SFG rickettsial DNA in these ticks was detected with rOmpA and GltA gene polymerase chain reaction (PCR) assays. The rickettsial species were identified by sequencing PCR amplicons. Of 365 D. occidentalis, 90 (24.7%) contained R. rhipicephali DNA, 28 (7.7%) contained DNA of unclassified genotype 364D, two (0.55%) contained R. bellii DNA, and one (0.3%) contained R. rickettsii DNA. Of 10 D. variabilis, four (40%) contained only R. rhipicephali. Four new genotypes of R. rhipicephali were discovered. For the first time, we detected R. rickettsii in D. occidentalis. Our study provides the first molecular data on the prevalence and species identification of SFG rickettsiae circulating in populations of these California ticks. Because neither D. variabilis nor R. rickettsii were abundant, 364D should be evaluated further as a potential cause of human SFG rickettsioses in southern California.

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Available from: Barry D Hess, Dec 19, 2013
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    • "Herein, all A. dubitatum ticks were originally infected by R. bellii, and even under these circumstances, some of them acquired and maintained the R. rickettsii infection through transstadial perpetuation. Natural infection by two or even three Rickettsia species in a single tick specimen has been reported in the literature, including R. bellii and a R. parkeri-like agent infecting an Amblyomma ovale specimen (Szabó et al., 2013), R. rickettsii and Rickettsia amblyommii infecting an A. americanum specimen (Berrada et al., 2011), R. bellii and Rickettsia rhipicephali infecting a D. variabilis specimen (Wikswo et al., 2008), and a triple infection by R. bellii, Rickettsia montanensis and R. rickettsii in a D. variabilis specimen (Carmichael and Fuerst, 2010). While 100% of the A. dubitatum ticks of the present study were infected by R. bellii, no guinea pig from the CG group became seropositive to R. bellii, while no R. bellii DNA was detected in lung samples from the GL, GN, and GA guinea pigs that died during the febrile period. "
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    ABSTRACT: Amblyomma dubitatum engorged females, naturally infected by Rickettsia bellii, were used to establish a laboratory colony. Larvae, nymphs, and adults were exposed to two strains of Rickettsia rickettsii by feeding on needle-inoculated guinea pigs, and thereafter reared on uninfected guinea pigs. After acquisition feeding, engorged larvae and nymphs molted to nymphs and adults, respectively, which were shown to be infected (confirming transstadial perpetuation), and were able to transmit both strains of R. rickettsii to uninfected animals, as demonstrated by clinical, serological, and molecular analyses. However, the larval, nymphal, and adult stages of A. dubitatum showed to be only partially susceptible to R. rickettsii infection, since in all cases, only part of the ticks became infected by this agent, after being exposed to rickettsemic animals. While transovarial transmission of R. rickettsii was inefficient in the A. dubitatum engorged females of the present study, 100% of these females passed R. bellii transovarially. Because it has been reported that a primary infection by a Rickettsia species would preclude transovarial transmission of a second Rickettsia species, it is likely that the ineffectiveness of A. dubitatum to perpetuate R. rickettsii by transovarial transmission was related to its primary infection by R. bellii; however, it could also be related to unknown factors inherent to A. dubitatum. The relevance of A. dubitatum as a natural vector of R. rickettsii to humans or animals is discussed.
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    • "Both the adult and immature stages of this tick will feed on humans and both are capable of transmitting rickettsial pathogens. Rickettsia rickettsii-infected R. sanguineus have been associated with RMSF cases from Arizona (Demma et al., 2005), California (Wikswo et al., 2008) and Georgia (Garrison et al., 2007). Rickettsia rickettsii prevalences in the brown dog ticks in these studies were higher than those reported for D. variabilis, the vector species traditionally implicated in RMSF transmission. "
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    ABSTRACT: The risk of contracting several tick-borne diseases, including Lyme disease, varies greatly among eastern US states because of regional variation in the abundance of key vector tick species. Moreover, these patterns of geographic risk are changing because tick distributions are in flux. Improving health provider knowledge of tick species distributions, and of tick-borne diseases other than Lyme disease, would lead to better diagnosis, treatment and reporting of these diseases, particularly in the south-eastern United States.
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    • "Rickettsia rhipicephali has been detected in R. sanguineus , D. occidentalis, D. variabilis and D. andersoni from the United States and Canada. (Burgdorfer et al., 1975; Wikswo et al., 2008; Shapiro et al., 2010). This SFGR has also been detected in Rhipicephalus lunulatus from Central African Republic (Cazorla et al., 2008). "
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    ABSTRACT: Spotted fever group rickettsioses (SFGR) are infections caused by established and emerging human pathogens worldwide. These rickettsial agents are transmitted to humans via arthropods and may result in mild to severe and potentially fatal diseases. Spotted fever group rickettsioses are characterized by similar clinical features, including fever, rash, headache and myalgias, with the development of an inoculation eschar in many, but not all cases. Endemic rickettsial infections do occur but are infrequent in Canada, in contrast to the United States, where these infections are far more prevalent. Travel-associated rickettsioses, however, are being diagnosed with increasing frequency in Canadian travellers returning from international trips abroad, in particular in travellers returning from Africa. The diagnosis of rickettsial infections can be challenging owing to the non-specific nature of the clinical symptoms and the requirement for specialized testing. Serology cannot distinguish between the approximately 20 spotted fever group rickettsial species currently known or suspected to be capable of causing human infection. Molecular testing is required to determine the rickettsial species responsible for infection, but requires greater effort on the part of the clinician to collect appropriate samples, including cutaneous skin swabs from under the eschar or skin punch biopsies of the eschar or rash. Infections with spotted fever group rickettsiae likely occur more commonly than currently recognized and should be considered in patients with appropriate symptoms and exposure histories.
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