Title: Species composition and temporal distribution of adult ixodid ticks and prevalence of <i>Borrelia burgdorferi</i> sensu lato and <i>Rickettsia</i> species in Orange County, California
Abstract: Journal of Vector EcologyVolume 42, Issue 1 p. 189-192 Scientific NoteFree Access Species composition and temporal distribution of adult ixodid ticks and prevalence of Borrelia burgdorferi sensu lato and Rickettsia species in Orange County, California Sarah A. Billeter, Sarah A. Billeter [email protected] California Department of Public Health, Vector-Borne Disease Section, Ontario, CA 91764-5429 U.S.A.Search for more papers by this authorMelissa Hardstone Yoshimizu, Melissa Hardstone Yoshimizu California Department of Public Health, Vector-Borne Disease Section, Richmond, CA 94804-6403 U.S.A.Search for more papers by this authorRenjie Hu, Renjie Hu California Department of Public Health, Vector-Borne Disease Section, Ontario, CA 91764-5429 U.S.A.Search for more papers by this author Sarah A. Billeter, Sarah A. Billeter [email protected] California Department of Public Health, Vector-Borne Disease Section, Ontario, CA 91764-5429 U.S.A.Search for more papers by this authorMelissa Hardstone Yoshimizu, Melissa Hardstone Yoshimizu California Department of Public Health, Vector-Borne Disease Section, Richmond, CA 94804-6403 U.S.A.Search for more papers by this authorRenjie Hu, Renjie Hu California Department of Public Health, Vector-Borne Disease Section, Ontario, CA 91764-5429 U.S.A.Search for more papers by this author First published: 15 May 2017 https://doi.org/10.1111/jvec.12255Citations: 11AboutSectionsPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Ticks (Acari: Ixodidae) can transmit a diverse group of pathogens and are considered one of the most important arthropod vectors of human diseases, second only to mosquitoes. One of the most commonly reported tick-borne illnesses in the United States, Lyme disease, is caused by Borrelia burgdorferi sensu stricto (ss), which is transmitted by ticks in the Ixodes ricinus complex (Mead 2015). Ixodes scapularis, the blacklegged tick, is considered the primary vector of B. burgdorferi ss in the northeastern and north-central United States and I. pacificus, the western blacklegged tick, is the primary vector in western states. In the United States alone, more than 30,000 cases of Lyme disease are reported each year but it is believed that the actual number of cases may reach as high as 300,000 (Mead 2015). In California, members of the B. burgdorferi sensu lato (sl) complex, including B. burgdorferi ss, B. americana, B. bissettiae (formerly B. bissettii), B. californiensis, B. carolinensis, and several uncharacterized genospecies have been detected in I. pacificus and mammals throughout the state (Lane et al. 2013, Foley et al. 2014, Padgett et al. 2014, Swei et al. 2015). Two pathogenic tick-borne Rickettsia species are also known to occur in California: R. rickettsii, the causative agent of Rocky Mountain spotted fever (RMSF), documented in Dermacentor species and R. philipii (formerly Rickettsia sp. 364D), likely transmitted by the Pacific Coast tick, Dermacentor occidentalis (Shapiro et al. 2010, Johnston et al. 2013, Padgett et al. 2016). Between 2006 and 2007, Wikswo et al. (2008) screened D. occidentalis collected from five southern California counties and demonstrated R. philipii DNA in 28 (7.7%) of 365 adult ticks tested. To understand the regional risk of tick exposure and tick-borne diseases, biologists from the California Department of Public Health, Vector-Borne Disease Section (CDPH-VBDS) focused on a well-used park in southern California. Situated between Corona del Mar and Laguna Beach in Orange County, Crystal Cove State Park provides access to 3.2 miles of beaches and hiking trails through 2,400 acres of native wilderness. Hikers, campers, mountain bikers, and equestrians frequently use the more than 18 miles of trails located within the park. Additionally, our records indicate the park harbors a high density of ticks, including those that potentially vector human disease. For this study, we determined species composition and temporal distribution of adult ticks and evaluated the transmission risk of Borrelia and Rickettsia species (spp.), the causative agents of the most frequently reported tick-borne diseases in California. The study was conducted over a three-year period, from July, 2013 through June, 2016, and tick collections were performed every two to four weeks (average: three weeks; 51 visits total) as weather permitted. Ticks were collected along Moro Canyon Trail (start site latitude: 33.56455, longitude: −117.817779; elevation: 13 m) between the junctions of Moro Ridge and East Cut Across trailheads. Moro Canyon Trail flora is a mix of coastal sage scrub and riparian woodlands consisting of oak, sycamore, and willow trees. Each collection period lasted approximately one person-hour and efforts were made to begin collecting at approximately the same time each visit (between 10:00 and 11:00). Ticks were collected from vegetation, leaf litter, or other substrates along the trail using a 1 m2 white, flannel flag on both the uphill and downhill slope. Ixodes pacificus were either kept alive or placed directly in a vial containing 70% ethanol. All other tick species were placed directly in ethanol. A subset of I. pacificus and D. occidentalis was tested for Borrelia and Rickettsia species, respectively, either by the CDPH-VBDS Laboratory or the CDPH-Viral and Rickettsial Disease Laboratory (VRDL). Ixodes pacificus were initially screened for Borrelia spp. using a direct fluorescent antibody assay (DFA) protocol (Padgett and Bonilla 2011) and if a presumptive positive was obtained, ticks were then tested using a real-time polymerase chain reaction (PCR) targeting a region of the 16S rDNA gene (Barbour et al. 2009). The PCR technique utilized allowed for differentiation between the B. burgdorferi sl complex and B. miyamotoi, a relapsing fever spirochete. Dermacentor occidentalis were tested for Rickettsia spp. infection using PCR protocols previously described (Padgett et al. 2016). Sequencing was performed for all Rickettsia-positive samples to specifically distinguish R. philipii from other spotted fever group rickettsiae (SFGR). A total of 1,900 adult ticks consisting of five species was collected over the course of the study (Table 1). Tick species recovered in order of abundance were I. pacificus, followed by D. occidentalis and D. variabilis. In addition, two Haemaphysalis leporispalustris and a single specimen of I. spinipalpis were collected. Ixodes pacificus adults were flagged from November through May (a single female was collected June 12, 2015), with the highest number collected in December (Figure 1). Adult D. occidentalis were present in the park from September (a single female was collected August 14, 2015) through July. Dermacentor occidentalis adult activity peaked in March. Few D. variabilis (54) were collected during the study period and were found March through August (data not shown). The female and male H. leporispalustris were collected in August, 2013 and May, 2014, respectively, and the lone female I. spinipalpis was recovered in March, 2014. Table 1. Species composition of adult ixodid ticks collected at Crystal Cove State Park, Orange County, CA, July, 2013 – June, 2016. Tick species Total collected Total females Total males Dermacentor occidentalis 918 485 433 Dermacentor variabilis 54 30 24 Ixodes pacificus 925 432 493 Ixodes spinipalpis 1 1 – Haemaphysalis leporispalustris 2 1 1 Total 1,900 949 951 Figure 1Open in figure viewerPowerPoint Temporal distribution of Dermacentor occidentalis and Ixodes pacificus at Crystal Cove State Park, Orange County, California, July, 2013 – June, 2016. Of the 233 I. pacificus tested for Borrelia spp., only two (0.9%) harbored detectable B. burgdorferi sl DNA (Table 2). Rickettsia philipii and R. rhipicephali DNA were found in nine (5.3%) and 50 (29.6%) of the 169 D. occidentalis tested, respectively. Sequencing was unable to confirm the identity of the SFGR in nine samples. Table 2. Prevalence of Borrelia and Rickettsia species in adult ixodid ticks from Crystal Cove State Park, Orange County, CA, July, 2013 – June, 2016. Tick species Number of ticks tested Borrelia positives (%) Rickettsia positives (%) Organism(s) detected Dermacentor occidentalis 169 NDa 68 (40.2%) R. philipii - 9 R. rhipicephali - 50 Undifferentiated SFGRb - 9 Ixodes pacificus 233 2 (0.9%) NDa B. burgdorferi sensu lato aND = testing not performed. bSFGR = spotted fever group Rickettsia. Our results demonstrated that questing adult ticks are present in El Moro Canyon, Crystal Cove State Park during most of the year. These findings are consistent with previous reports regarding the seasonality of I. pacificus and D. occidentalis in other southern California counties. In Santa Barbara County, I. pacificus were collected between November and May from the Santa Ynez Mountains, and in Los Angeles County, adults were active December through late April in the Santa Monica Mountains, with density peaking in February and March (MacDonald and Briggs 2016). In an earlier study, Lang (1999) reported the presence of I. pacificus in San Diego County from November through April with numbers peaking in February and March, and D. occidentalis were active from November through June with numbers peaking March and April. As seen with similar studies, tick abundance fluctuated from year to year at Crystal Cove State Park. Between July, 2013 and June, 2014, 558 D. occidentalis were collected, whereas during the following cycle of tick activity (July, 2014 – June, 2015), only 142 adults were collected. Variations related to host availability and activity and changes in the micro- and macroenvironment due to the extreme drought conditions occurring throughout the state of California are likely factors that contributed to the fluctuation in the D. occidentalis population. Previous findings have also shown that repeated sampling removal at a single location can reduce the abundance of questing adult ticks (Kramer et al. 1993). The numbers of I. pacificus remained relatively stable, however, suggesting the habitat at Moro Canyon trail is more conducive for this tick species. Most ticks (1,761/1,900; 92.7%) were recovered in short grasses and brush along the shaded, uphill slope of the trail; habitat previously shown to be favorable for I. pacificus in north coastal California due to their need for lower temperatures and higher humidity (Li et al. 2000). Additionally, Lane et al. (2013) demonstrated that I. pacificus were more abundant than D. occidentalis in Los Angeles County in woodland-grass, vegetation common for this portion of the study site. Many factors may have contributed to the fluctuation in D. occidentalis abundance and additional long-term follow-up sampling may be warranted to further our understanding of the population dynamics of this tick species. Despite the abundance of I. pacificus at Crystal Cove State Park, B. burgdorferi sl was found in only a small percentage (∼1%) of tested adults (Table 2). Borrelia miyamotoi, a relapsing fever agent that is also transmitted by the western blacklegged tick, was not detected although it has been reported in California I. pacificus previously (Fedorova et al. 2014, Padgett et al. 2014, Eshoo et al. 2015, Salkeld et al. 2015). A similar Borrelia infection prevalence was found in I. pacificus from nearby Los Angeles County: seven (0.29%) of 2,392 ticks were infected with B. burgdorferi sl but none harbored detectable B. miyamotoi (Lane et al. 2013). Additional analyses identified B. burgdorferi ss, B. americana, and a genospecies related to B. americana circulating in these I. pacificus. The statewide prevalence of B. burgdorferi sl and B. miyamotoi in adult I. pacificus is 0.6% and 0.8%, respectively (Padgett et al. 2014). It was proposed that individuals were more likely to come into contact with Borrelia-infected ticks in north and central coastal counties and the Sierra Nevada foothill region than in southern California (Padgett et al. 2014). Further characterization of the two infected I. pacificus collected in this study is necessary. Regardless, the B. burgdorferi sl infection prevalence is low suggesting that the risk of acquiring Lyme disease in Crystal Cove State Park is minimal. Spotted fever group rickettsiae were present in almost half (40.2%) of examined D. occidentalis, including the detection of the human pathogen R. philipii. Rickettsia philipii, the causative agent of Pacific Coast tick fever, has been reported in 14 patients in California (Padgett et al. 2016). While the majority of these cases (13/14; 93%) have occurred in northern California (Shapiro et al. 2010, Johnston et al. 2013, Padgett et al. 2016), there was a reported human case in Orange County in 2013 (CDPH – VBDS 2013 Annual Report: http://www.cdph.ca.gov/programs/vbds/Documents/VBDSAnnualReport13.pdf). Rocky Mountain spotted fever, caused by R. rickettsii, and Pacific Coast tick fever are the only two human rickettsioses transmitted by Ixodidae known to occur in California. Rickettsia rhipicephali, detected in almost 30% of D. occidentalis in this study, has not been associated with human disease (Padgett et al. 2016) and the SFGR in nine samples could not be identified due to poor sequencing reads or insufficient DNA yield. We demonstrated that Crystal Cove State Park located in Orange County harbors diverse tick species and I. pacificus and D. occidentalis, two important vectors of human diseases, are abundant throughout most of year. Although the prevalence of disease-causing pathogens in tested ticks was low, the general public should be aware that ticks may be encountered at the park and take steps to prevent tick bites. Acknowledgments This study was supported by the Epidemiology and Laboratory Capacity for Infectious Diseases cooperative agreement number 5U50CK0004100CI000915 from the U.S. Centers for Disease Control and Prevention (Co PI's Jill Hacker and Kerry Padgett). 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