Rickettsia Species Isolated from Dermacentor occidentalis (Acari: Ixodidae) from California

Abstract

The Pacific Coast tick (Dermacentor occidentalis Marx, 1892) is one of the most widely distributed and frequently encountered tick species in California. This tick is the primary vector of an unclassified spotted fever group rickettsial pathogen, designated currently as Rickettsia 364D, the etiologic agent of a recently recognized tick-borne rickettsiosis known as Pacific Coast tick fever. Despite intensified interest in this pathogen, important questions remain regarding its taxonomic status and possible variations in genotype among different strains that could influence its pathogenicity. Only the extensively passaged prototypical isolate (strain 364-D) is widely available to rickettsiologists and public health scientists worldwide. To achieve a larger, more geographically diverse, and contemporary collection of strains, 1,060 questing adult D. occidentalis ticks were collected from 18 sites across six counties in northern and southern California in 2016 and 2017. Fourteen ticks (1.3%) yielded DNA of Rickettsia 364D and from these, 10 unique isolates from Lake and Orange counties were obtained. Additionally, Rickettsia rhipicephali was detected in 108 (10.2%) ticks, from which eight isolates were obtained, and Rickettsia bellii in six (0.6%), from which three isolates were obtained. The panel of recently acquired, low-passage strains of Rickettsia 364D derived from this study could enhance opportunities for investigators to accurately determine the taxonomic standing of this agent and to develop specific diagnostic assays for detecting infections with Rickettsia 364D in ticks and humans.

Bio-efficacy of permethrin/tetramethrin and lambda-cyhalothrin treatments in habitats of hard ticks (Acari, Ixodidae) populations with confirmed Borrelia spp. infection

“…Increased number of reported cases of tick-borne diseases is closely realed with altered behavior patterns and zoogeographical prevalence of some tick species during the past few years (Paddock et al 2018). In this study, three tick species were identi ed with I. ricinus being predominant at all localities.…”

Identification ofRickettsiaspp. andBabesia conradaeinDermacentorspp. Collected from Dogs and Cats Across the United States

“…Besides R. rickettsii , other SFGR can cause significant disease in humans and therefore may be contributing to the rise in reported cases of rickettsiosis since many SFGR cross-react on commonly used serologic assays (Moncayo et al 2010 ). Two such examples include R. philipii ( Rickettsia 364D), the causative agent of Pacific Coast tick fever, transmitted by D. occidentalis along its range in California, and R. parkeri transmitted by A. maculatum in the southeastern United States (Paddock et al 2010 , 2018 , Stromdahl et al 2011 , Yoshimizu and Billeter 2018 ).…”

“…Reports and concern for spotted fever group Rickettsia (SFGR) other than R. rickettsii as a significant cause of human disease have grown over the last two decades (Delisle et al 2016 , CDC 2018). For instance, R. philipii ( Rickettsia 364D) transmitted by Dermacentor occidentalis in California may cause fever, headache, or a maculopapular rash, while Rickettsia parkeri , transmitted by Amblyomma maculatum across its southeastern range, can cause similar signs in humans (Parola et al 2013 , Paddock et al 2018 , Yoshimizu and Billeter 2018 ). In addition, a human case report describes rickettsiosis following a D. variabilis bite caused by R. montanensis , and recently, a novel Rickettsia sp.…”

A Novel TaqMan Assay for Detection ofRickettsia364D, the Etiologic Agent of Pacific Coast Tick Fever

“…Much about the ecology of Rickettsia 364D remains unknown. To date, D. occidentalis is the only tick species in which Rickettsia 364D has been detected (5). Other human-biting tick species coexist with D. occidentalis in areas where Rickettsia 364D has been identified, and some of these species have been shown to be competent vectors of other, closely related rickettsial species.…”