Rickettsia species identified in adult, host-seeking Dermacentor occidentalis (Acari: Ixodidae) from Baja California, Mexico, and Oregon and Washington, United States

The Pacific Coast tick (Dermacentor occidentalis Marx, 1892) is a frequently encountered and commonly reported human-biting tick species that has been recorded from most of California and parts of southwestern Oregon, southcentral Washington, and northwestern Mexico. Although previous investigators have surveyed populations of D. occidentalis for the presence of Rickettsia species across several regions of California, populations of this tick have not been surveyed heretofore for rickettsiae from Baja California, Oregon, or Washington. We evaluated 1,367 host-seeking, D. occidentalis adults collected from 2015 to 2022 by flagging vegetation at multiple sites in Baja California, Mexico, and Oregon and Washington, United States, using genus- and species-specific assays for spotted fever group rickettsiae. DNA of Rickettsia 364D, R. bellii, and R. tillamookensis was not detected in specimens from these regions. DNA of R. rhipicephali was detected in D. occidentalis specimens obtained from Ensenada Municipality in Baja California and southwestern Oregon, but not from Washington. All ompA sequences of R. rhipichephali that were amplified from individual ticks in southwestern Oregon were represented by a single genotype. DNA of the Ixodes pacificus rickettsial endosymbiont was amplified from specimens collected in southwestern Oregon and Klickitat County, Washington; to the best of our knowledge, this Rickettsia species has never been identified in D. occidentalis. Collectively, these data are consistent with a relatively recent introduction of Pacific Coast ticks in the northernmost extension of its recognized range.

Rickettsia tillamookensis (Rickettsiales: Rickettsiaceae) in Ixodes scapularis (Acari: Ixodidae) in Oklahoma

Some of the most prevalent arthropod-borne pathogens impacting humans in the United States are transmitted by Ixodes ticks. However, little is known regarding the Rickettsia species that inhabit Ixodes scapularis in the United States. The aim of this study was to screen adult I. scapularis collected in central Oklahoma over an 8-yr period for the presence of tick-borne rickettsial pathogens or potential pathogens. During 2014-2021, 112 adult specimens of I. scapularis were collected from central Oklahoma. Amplicons for Rickettsia spp. were amplified from 53 (47.3%) of the samples. Of the positive ticks, 42 (79.2%) amplicon-positive Rickettsia samples were 100% identical to Rickettsia buchneri, 10 (18.9%) were 100% identical to R. tillamookensis strain Tillamook 23, and 1 (1.9%) specimen showed high identity for Rickettsia amblyommatis. This study highlights the importance of considering Rickettsia-specific assays when assessing Ixodes species ticks for potential pathogens.

Anaplasma bovis-Like Infections in Humans, United States, 2015-2017

We detected the DNA of an Anaplasma bovis-like bacterium in blood specimens from 4 patients from the United States with suspected tickborne illnesses. Initial molecular characterization of this novel agent reveals identity to A. bovis-like bacteria detected in Dermacentor variabilis ticks collected from multiple US states.

Detection and Isolation of Rickettsia tillamookensis (Rickettsiales: Rickettsiaceae) From Ixodes pacificus (Acari: Ixodidae) From Multiple Regions of California

The western black-legged tick (Ixodes pacificus) is the most frequently identified human-biting tick species in the western United States and the principal vector of at least three recognized bacterial pathogens of humans. A potentially pathogenic Rickettsia species, first described in 1978 and recently characterized as a novel transitional group agent designated as Rickettsia tillamookensis, also exists among populations of I. pacificus, although the distribution and frequency of this agent are poorly known. We evaluated DNA extracts from 348 host-seeking I. pacificus nymphs collected from 9 locations in five California counties, and from 916 I. pacificus adults collected from 24 locations in 13 counties, by using a real-time PCR designed specifically to detect DNA of R. tillamookensis. DNA of R. tillamookensis was detected in 10 (2.9%) nymphs (95% CI: 1.6-5.2%) and 17 (1.9%) adults (95% CI: 1.2-3.0%) from 11 counties of northern California. Although site-specific infection rates varied greatly, frequencies of infection remained consistently low when aggregated by stage, sex, habitat type, or geographical region. Four novel isolates of R. tillamookensis were cultivated in Vero E6 cells from individual adult ticks collected from Alameda, Nevada, and Yolo counties. Four historical isolates, serotyped previously as 'Tillamook-like' strains over 40 yr ago, were revived from long-term storage in liquid nitrogen and confirmed subsequently by molecular methods as isolates of R. tillamookensis. The potential public health impact of R. tillamookensis requires further investigation.

Complete Genome Sequence of Rickettsia parkeri Strain Black Gap

A unique genotype of Rickettsia parkeri, designated R. parkeri strain Black Gap, has thus far been associated exclusively with the North American tick, Dermacentor parumapertus. The compete genome consists of a single circular chromosome with 1,329,522 bp and a G+C content of 32.5%.

Performance of Repeat BinaxNOW Severe Acute Respiratory Syndrome Coronavirus 2 Antigen Testing in a Community Setting, Wisconsin, November 2020-December 2020

Repeating the BinaxNOW antigen test for SARS-CoV-2 by two groups of readers within 30 minutes resulted in high concordance (98.9%) in 2,110 encounters. BinaxNOW test sensitivity was 77.2% (258/334) compared to real-time reverse transcription-polymerase chain reaction. Same day antigen testing did not significantly improve test sensitivity while specificity remained high.

Characterization of a novel transitional group Rickettsia species (Rickettsia tillamookensis sp. nov.) from the western black-legged tick, Ixodes pacificus

A previously unrecognized Rickettsia species was isolated in 1976 from a pool of Ixodes pacificus ticks collected in 1967 from Tillamook County, Oregon, USA. The isolate produced low fever and mild scrotal oedema following intraperitoneal injection into male guinea pigs (Cavia porcellus). Subsequent serotyping characterized this isolate as distinct from recognized typhus and spotted fever group Rickettsia species; nonetheless, the isolate remained unevaluated by molecular techniques and was not identified to species level for the subsequent 30 years. Ixodes pacificus is the most frequently identified human-biting tick in the western United States, and as such, formal identification and characterization of this potentially pathogenic Rickettsia species is warranted. Whole-genome sequencing of the Tillamook isolate revealed a genome 1.43 Mbp in size with 32.4 mol% G+C content. Maximum-likelihood phylogeny of core proteins places it in the transitional group of Rickettsia basal to both Rickettsia felis and Rickettsia asembonensis. It is distinct from existing named species, with maximum average nucleotide identity of 95.1% to R. asembonensis and maximum digital DNA-DNA hybridization score similarity to R. felis at 80.1%. The closest similarity at the 16S rRNA gene (97.9%) and sca4 (97.5%/97.6% respectively) is to Candidatus 'Rickettsia senegalensis' and Rickettsia sp. cf9, both isolated from cat fleas (Ctenocephalides felis). We characterized growth at various temperatures and in multiple cell lines. The Tillamook isolate grows aerobically in Vero E6, RF/6A and DH82 cells, and growth is rapid at 28 °C and 32 °C. Using accepted genomic criteria, we propose the name Rickettsia tillamookensis sp. nov., with the type strain Tillamook 23. Strain Tillamook 23 is available from the Centers for Disease Control and Prevention Rickettsial Isolate Reference Collection (WDCM 1093), Atlanta, GA, USA (CRIRC accession number RTI001^T) and the Collection de Souches de l'Unité des Rickettsies (WDCM 875), Marseille, France (CSUR accession number R5043). Using accepted genomic criteria, we propose the name Rickettsia tillamookensis sp. nov., with the type strain Tillamook 23 (=CRIRC RTI001=R5043).

Multi-Locus Sequence Typing of Ehrlichia chaffeensis Reveals Extensive Genotypic Variation across the United States

Ehrlichia chaffeensis causes human monocytic ehrlichiosis, and its principal vector is the Amblyomma americanum tick. The most frequently identified cases of ehrlichiosis come from the southeastern and south central states of the United States. In this study, a molecular typing system was developed that allows for the genetic differentiation of E. chaffeensis isolates. This multi-locus typing system included sequencing and analyzing intergenic regions ECH0033-ECH0035 and ECH0217-ECH0218, plus, variable genes variable length PCR target, 28-kDa, 120-kDa, and hemE. We examined a total of 31 unique isolates from humans and white-tailed deer, and eight DNA samples extracted from infected A. americanum collected from multiple states. This is the largest evaluation of E. chaffeensis isolates and their genotypes. Our findings show that when sequences of all six loci were concatenated and compared, the 39 samples could be separated into 23 genotypes and further grouped into six phylogenetic clades. The data in this study show no clear pattern between the geographic alignment with the genetic differentiation between the strains. As a result, this poses a challenge to understanding the spread of E. chaffeensis in the United States. Interestingly, our findings indicate that multiple strains from distant geographic origins share the same mutations, which suggests that the strains are being moved from one site to another by their hosts or vectors. In addition, we are seeing a northward shift in the lone star tick distribution in the United States. Last, some data also suggest minimal genetic mutations have occurred over time among strains that are within geographical proximity.

Reproductive incompatibility between Amblyomma maculatum (Acari: Ixodidae) group ticks from two disjunct geographical regions within the USA

The Amblyomma maculatum Koch group of ixodid ticks consists of three species: A. maculatum, A. triste, and A. tigrinum. However, since Koch described this group in 1844, the systematics of its members has been the subject of ongoing debate. This is especially true of A. maculatum and A. triste; recent molecular analyses reveal insufficient genetic divergence to separate these as distinct species. Further confounding this issue is the discovery in 2014 of A. maculatum group ticks in southern Arizona (AZ), USA, that share morphological characteristics with both A. triste and A. maculatum. To biologically evaluate the identity of A. maculatum group ticks from southern Arizona, we analyzed the reproductive compatibility between specimens of A. maculatum group ticks collected from Georgia (GA), USA, and southern Arizona. Female ticks from both Arizona and Georgia were mated with males from both the Georgia and Arizona Amblyomma populations, creating two homologous and two heterologous F1 cohorts of ticks: GA ♀/GA ♂, AZ ♀/AZ ♂, GA ♀/AZ ♂, and AZ ♀/GA ♂. Each cohort was maintained separately into the F2 generation with F1 females mating only with F1 males from their same cohort. Survival and fecundity parameters were measured for all developmental stages. The observed survival parameters for heterologous cohorts were comparable to those of the homologous cohorts through the F1 generation. However, the F1 heterologous females produced F2 egg clutches that did not hatch, thus indicating that the Arizona and Georgia populations of A. maculatum group ticks tested here represent different biological species.

Distribution and Occurrence of Amblyomma maculatum sensu lato (Acari: Ixodidae) and Rickettsia parkeri (Rickettsiales: Rickettsiaceae), Arizona and New Mexico, 2017-2019

Amblyomma maculatum Koch sensu lato (s.l.) ticks are the vector of Rickettsia parkeri in Arizona, where nine cases of R. parkeri rickettsiosis have been identified since the initial case in 2014. The current study sought to better define the geographic ranges of the vector and pathogen and to assess the potential public health risk posed by R. parkeri in this region of the southwestern United States. A total of 275 A. maculatum s.l. ticks were collected from 34 locations in four counties in Arizona and one county in New Mexico and screened for DNA of Rickettsia species. Rickettsia parkeri was detected in 20.4% of the ticks, including one specimen collected from New Mexico, the first report of R. parkeri in A. maculatum s.l. from this state. This work demonstrates a broader distribution of A. maculatum s.l. ticks and R. parkeri in the southwestern United States than appreciated previously to suggest that R. parkeri rickettsiosis is underrecognized in this region.

Rickettsia parkeri (Rickettsiales: Rickettsiaceae) in the Sky Islands of West Texas

Rickettsia parkeri, a tick-borne pathogen distributed throughout several countries of the Americas, causes a mild to moderately severe, eschar-associated spotted fever rickettsiosis. Although most U.S. cases of R. parkeri rickettsiosis are reported from southeastern states, some have been reported recently from remote regions of southern Arizona. These cases are linked to R. parkeri-infected ticks of the Amblyomma maculatum (Acari: Ixodidae) group found in several isolated mountain ranges of southern Arizona and New Mexico, referred to as 'sky islands'. Archival records also document ticks of the A. maculatum group collected from domestic and wild animals in West Texas. We surveyed sites in two sky island chains of Jeff Davis and Brewster counties to document the off-host occurrence of these ticks and identify the presence of R. parkeri in the Trans-Pecos region of Texas. During August 2019, 43 adult A. maculatum group ticks were flagged from vegetation or removed from a road-killed, female mule deer. Of 39 samples evaluated by PCR, eight contained a partial sca0 sequence with complete identity to R. parkeri and two with complete identity to 'Candidatus Rickettsia andeanae', a species of undetermined pathogenicity. Four isolates of R. parkeri were obtained using cell culture. Persons at risk for R. parkeri rickettsiosis include those who work or recreate in these mountains, such as hikers, backpackers, research scientists, foresters, and border enforcement personnel. Additional investigations are needed to define the distribution of these medically important arthropods in other parts of the southwestern United States and northern Mexico.

Integrating population genetic structure, microbiome, and pathogens presence data in Dermacentor variabilis

Tick-borne diseases (TBDs) continue to emerge and re-emerge in several regions of the world, highlighting the need for novel and effective control strategies. The development of effective strategies requires a better understanding of TBDs ecology, and given the complexity of these systems, interdisciplinary approaches are required. In recent years, the microbiome of vectors has received much attention, mainly because associations between native microbes and pathogens may provide a new promising path towards the disruption of pathogen transmission. However, we still do not fully understand how host genetics and environmental factors interact to shape the microbiome of organisms, or how pathogenic microorganisms affect the microbiome and vice versa. The integration of different lines of evidence may be the key to improve our understanding of TBDs ecology. In that context, we generated microbiome and pathogen presence data for Dermacentor variabilis, and integrated those data sets with population genetic data, and metadata for the same individual tick specimens. Clustering and multivariate statistical methods were used to combine, analyze, and visualize data sets. Interpretation of the results is challenging, likely due to the low levels of genetic diversity and the high abundance of a few taxa in the microbiome. Francisella was dominant in almost all ticks, regardless of geography or sex. Nevertheless, our results showed that, overall, ticks from different geographic regions differ in their microbiome composition. Additionally, DNA of Rickettsia rhipicephali, R. montanensis, R. bellii, and Anaplasma spp., was detected in D. variabilis specimens. This is the first study that successfully generated microbiome, population genetics, and pathogen presence data from the same individual ticks, and that attempted to combine the different lines of evidence. The approaches and pre-processing steps used can be applied to a variety of taxa, and help better understand ecological processes in biological systems.

COVID-19 Among Workers in Meat and Poultry Processing Facilities - 19 States, April 2020

Congregate work and residential locations are at increased risk for infectious disease transmission including respiratory illness outbreaks. SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), is primarily spread person to person through respiratory droplets. Nationwide, the meat and poultry processing industry, an essential component of the U.S. food infrastructure, employs approximately 500,000 persons, many of whom work in proximity to other workers (1). Because of reports of initial cases of COVID-19, in some meat processing facilities, states were asked to provide aggregated data concerning the number of meat and poultry processing facilities affected by COVID-19 and the number of workers with COVID-19 in these facilities, including COVID-19-related deaths. Qualitative data gathered by CDC during on-site and remote assessments were analyzed and summarized. During April 9-27, aggregate data on COVID-19 cases among 115 meat or poultry processing facilities in 19 states were reported to CDC. Among these facilities, COVID-19 was diagnosed in 4,913 (approximately 3%) workers, and 20 COVID-19-related deaths were reported. Facility barriers to effective prevention and control of COVID-19 included difficulty distancing workers at least 6 feet (2 meters) from one another (2) and in implementing COVID-19-specific disinfection guidelines.* Among workers, socioeconomic challenges might contribute to working while feeling ill, particularly if there are management practices such as bonuses that incentivize attendance. Methods to decrease transmission within the facility include worker symptom screening programs, policies to discourage working while experiencing symptoms compatible with COVID-19, and social distancing by workers. Source control measures (e.g., the use of cloth face covers) as well as increased disinfection of high-touch surfaces are also important means of preventing SARS-CoV-2 exposure. Mitigation efforts to reduce transmission in the community should also be considered. Many of these measures might also reduce asymptomatic and presymptomatic transmission (3). Implementation of these public health strategies will help protect workers from COVID-19 in this industry and assist in preserving the critical meat and poultry production infrastructure (4).

Molecular Confirmation of Rickettsia parkeri in Amblyomma ovale Ticks, Veracruz, Mexico

We found Rickettsia parkeri in Amblyomma ovale ticks collected in Veracruz, Mexico, in 2018. We sequenced gene segments of gltA, htrA, sca0, and sca5; phylogenetic reconstruction revealed near-complete identity with R. parkeri strain Atlantic Rainforest. Enhanced surveillance is needed in Mexico to determine the public health relevance of this bacterium.

Rickettsia and Anaplasma species in Dermacentor andersoni ticks from Washington

Dermacentor andersoni, the Rocky Mountain wood tick, occurs predominantly in the northwestern United States and southwestern Canada. There are relatively few contemporary data to evaluate the occurrence of Rickettsia and Anaplasma species in D. andersoni in western North America, and even less information about these associations in the state of Washington, where this tick species is widely distributed and often bites humans. We used PCR assays to detect DNA of Rickettsia and Anaplasmataceae bacteria in 203 adult D. andersoni ticks collected from 17 sites in 9 counties of Washington between May 2012 and May 2015. Of these, 56 (27.6 %) were infected with a Rickettsia species and 3 (5.4 %) with a member of the Anaplasmataceae family. Rickettsia peacockii, R. bellii and R. rhipicephali were found in 17.7 %, 4.9 %, and 4.4 % of the Rickettsia positive ticks, respectively. Coinfections of R. bellii with R. peacockii or R. rhipicephali were identified in 6 ticks. Of the Anaplasmataceae-positive ticks, one was identified as being infected with Anaplasma phagocytophilum AP-Variant 1. No ticks were infected with a recognized human or animal pathogen, including R. rickettsii, A. phagocytophilum-ha, A. bovis, or A. marginale.

Rickettsia parkeri and Candidatus Rickettsia andeanae in Tick of the Amblyomma maculatum Group, Mexico

We report Rickettsia parkeri and Candidatus Rickettsia andeanae in ticks of the Amblyomma maculatum group collected from dogs in Sonora, Mexico. Molecular characterization of these bacteria was accomplished by DNA amplification and sequence analysis of portions of the rickettsial genes gltA, htrA, ompA, and ompB.

First Report of the Introduction of an Exotic Tick, Amblyomma coelebs (Acari: Ixodidae), Feeding on a Human Traveler Returning to the United States from Central America

Introduction of ticks into the United States that can carry disease-causing pathogens to humans, companion animals, and wildlife has accelerated in recent years, mostly due to globalization, frequency of travel, and a rise in legal and illegal animal trades. We hereby report for the first time introduction of a live fully engorged Amblyomma coelebs feeding on a human into the United States from Central America. Amblyomma coelebs is geographically distributed in the Neotropical region and reaches the southern states of Mexico. This species is capable of transmitting a number of pathogens of public health and veterinary importance including spotted fever group rickettsiae, raising concern that A. coelebs, if it became established in the United States, might also be able to carry these pathogens. Considering the risks of exotic ticks as vectors of numerous pathogens and their potential to establish new populations under conducive climatic and habitat conditions, rigorous inspection practices of imported livestock and pet animals at ports of entry are vital. It is also important for travelers and practitioners to develop a heightened awareness of the public health risks associated with the unintended importation of exotic ticks and the potential such parasites have for breaching United States biosecurity defenses.

Multistate Survey of American Dog Ticks (Dermacentor variabilis) for Rickettsia Species

Dermacentor variabilis, a common human-biting tick found throughout the eastern half and along the west coast of the United States, is a vector of multiple bacterial pathogens. Historically, D. variabilis has been considered a primary vector of Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever. A total of 883 adult D. variabilis, collected between 2012 and 2017 from various locations in 12 states across the United States, were screened for rickettsial DNA. Tick extracts were evaluated using three real-time PCR assays; an R. rickettsii-specific assay, a Rickettsia bellii-specific assay, and a Rickettsia genus-specific assay. Sequencing of ompA gene amplicons generated using a seminested PCR assay was used to determine the rickettsial species present in positive samples not already identified by species-specific real-time assays. A total of 87 (9.9%) tick extracts contained R. bellii DNA and 203 (23%) contained DNA of other rickettsial species, including 47 (5.3%) with Rickettsia montanensis, 11 (1.2%) with Rickettsia amblyommatis, 2 (0.2%) with Rickettsia rhipicephali, and 3 (0.3%) with Rickettsia parkeri. Only 1 (0.1%) tick extract contained DNA of R. rickettsii. These data support multiple other contemporary studies that indicate infrequent detection of R. rickettsii in D. variabilis in North America.

Rickettsia parkeri in Dermacentor parumapertus Ticks, Mexico

During a study to identify zoonotic pathogens in northwestern Mexico, we detected the presence of a rickettsial agent in Dermacentor parumapertus ticks from black-tailed jackrabbits (Lepus californicus). Comparison of 4 gene sequences (gltA, htrA, ompA, and ompB) of this agent showed 99%–100% identity with sequences of Rickettsia parkeri.

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

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.

Distribution and Establishment of the Lone Star Tick in Connecticut and Implications for Range Expansion and Public Health

In the United States, the lone star tick, Amblyomma americanum (L.) (Acari: Ixodidae), is an aggressive southeastern species whose range has reportedly been steadily expanding northward. The number of A. americanum specimens submitted to the Tick Testing Laboratory (TTL) at the Connecticut Agricultural Experiment Station (CAES) increased by 58% from the period of 1996-2006 (n = 488) to 2007-2017 (n = 773), mainly from Fairfield County in the southwestern corner of the state. The greatest numbers of A. americanum submissions to the CAES-TTL were from the City of Norwalk and a few adjacent municipalities. We also report the discovery of a large infestation of adult and nymphal lone star ticks detected on a dead male white-tailed deer, Odocoileus virginianus (Zimmerman) (Artiodactyla: Cervidae), on Manresa Island, Norwalk, in June 2017, indicating a long established, undetected population along the southwestern coast. A sample of nymphal and adult host-seeking A. americanum collected July 2017 from Manresa Island were tested and a proportion were positive for Ehrlichia chaffeensis, Ehrlichia ewingii, and Anaplasma phagocytophilum. The A. americanum tick and its associated disease pathogens are expected to become an increasing public health concern in southern New England.

Prevalence and distribution of seven human pathogens in host-seeking Ixodes scapularis (Acari: Ixodidae) nymphs in Minnesota, USA

In the north-central United States, the blacklegged tick (Ixodes scapularis) is currently known to vector seven human pathogens. These include five bacteria (Borrelia burgdorferi sensu stricto, Borrelia mayonii, Borrelia miyamotoi, Anaplasma phagocytophilum, Ehrlichia muris eauclairensis), one protozoan (Babesia microti) and one virus (Powassan). We sought to assess the prevalence and distribution of these pathogens in host-seeking nymphs collected throughout Minnesota, a state on the northwestern edge of the tick's expanding range, where reported cases of I. scapularis-borne diseases have increased in incidence and geographic range over the past decade. Among the 1240 host-seeking I. scapularis nymphs that we screened from 64 sites, we detected all seven pathogens at varying frequencies. Borrelia burgdorferi s.s. was the most prevalent and geographically widespread, found in 25.24% of all nymphs tested. Anaplasma phagocytophilum and Babesia microti were also geographically widespread, but they were less prevalent than Bo. burgdorferi s.s. (detected in 6.29% and 4.68% of ticks, respectively). Spatial clusters of sites with high prevalence for these three pathogens were identified in the north-central region of the state. Prevalence was less than 1.29% for each of the remaining pathogens. Two or more pathogens were detected in 90 nymphs (7.26%); coinfections with Bo. burgdorferi s.s. and either A. phagocytophilum (51 nymphs, 4.11%) or Ba. microti (43 nymphs, 3.47%) were the most common combinations. The distribution and density of infected ticks mirrors the distribution of notifiable tick-borne diseases in Minnesota and provides information on the distribution and prevalence of recently described human pathogens.

Proposal to reclassify Ehrlichia muris as Ehrlichia muris subsp. muris subsp. nov. and description of Ehrlichia muris subsp. eauclairensis subsp. nov., a newly recognized tick-borne pathogen of humans

We have previously described a novel taxon of the genus Ehrlichia (type strain WisconsinT), closely related to Ehrlichia muris, that causes human ehrlichiosis among patients with exposures to ticks in the upper midwestern USA. DNA from this bacterium was also detected in Ixodes scapularis and Peromyscus leucopus collected in Minnesota and Wisconsin. To determine the relationship between the E. muris-like agent (EMLA) and other species of the genus Ehrlichia phenotypic, genotypic and epidemiologic comparisons were undertaken, including sequence analysis of eight gene loci (3906 nucleotides) for 39 EMLA DNA samples and the type strain of E. muris AS145T. Three loci were also sequenced from DNA of nine strains of E. muris from mouse spleens from Japan. All sequences from E. muris were distinct from homologous EMLA sequences, but differences between them were less than those observed among other species of the genus Ehrlichia. Phenotypic comparison of EMLA and E. muris revealed similar culture and electron microscopic characteristics, but important differences were noted in their geographic distribution, ecological associations and behavior in mouse models of infection. Based on these comparisons, we propose that type strain WisconsinT represents a novel subspecies, Ehrlichia murissubsp. eauclairensis,subsp. nov. This strain is available through the Centers for Disease Control and Prevention Rickettsial Isolate Reference Collection (CRIRC EMU002T) and through the Collection de Souches de l'Unité des Rickettsies (CSURP2883 T). The subspecies Ehrlichia murissubsp. muris subsp. nov. is automatically created and the type strain AS145T is also available through the same collections (CRIRC EMU001T, CSUR E2T). Included is an emended description of E. muris.

Unique Strain of Rickettsia parkeri Associated with the Hard Tick Dermacentor parumapertus Neumann in the Western United States

In 1953, investigators at the Rocky Mountain Laboratories in Hamilton, MT, described the isolation of a spotted fever group Rickettsia (SFGR) species from Dermacentor parumapertus ticks collected from black-tailed jackrabbits (Lepus californicus) in northern Nevada. Several decades later, investigators characterized this SFGR (designated the parumapertus agent) by using mouse serotyping methods and determined that it represented a distinct rickettsial serotype closely related to Rickettsia parkeri; nonetheless, the parumapertus agent was not further characterized or studied. To our knowledge, no isolates of the parumapertus agent remain in any rickettsial culture collection, which precludes contemporary phylogenetic placement of this enigmatic SFGR. To rediscover the parumapertus agent, adult-stage D. parumapertus ticks were collected from black-tailed jackrabbits shot or encountered as roadkills in Arizona, Utah, or Texas from 2011 to 2016. A total of 339 ticks were collected and evaluated for infection with Rickettsia species. Of 112 D. parumapertus ticks collected in south Texas, 16 (14.3%) contained partial ompA sequences with the closest identity (99.6%) to Rickettsia sp. strain Atlantic rainforest Aa46, an SFGR that is closely related or identical to an SFGR species that causes a mild rickettsiosis in several states of Brazil. A pure isolate, designated strain Black Gap, was cultivated in Vero E6 cells, and sequence analysis of the rrs, gltA, sca0, sca5, and sca4 genes also revealed the closest genetic identity to Rickettsia sp. Atlantic rainforest Aa46. Phylogenetic analysis of the five concatenated rickettsial genes place Rickettsia sp. strain Black Gap and Rickettsia sp. Atlantic rainforest Aa46 with R. parkeri in a distinct and well-supported clade.IMPORTANCE We suggest that Rickettsia sp. Black Gap and Rickettsia sp. Atlantic rainforest Aa46 represent nearly identical strains of R. parkeri and that Rickettsia sp. Black Gap or a very similar strain of R. parkeri represents the parumapertus agent. The close genetic relatedness among these taxa, as well as the response of guinea pigs infected with the Black Gap strain, suggests that R. parkeri Black Gap could cause disease in humans. The identification of this organism could also account, at least in part, for the remarkable differences in severity ascribed to Rocky Mountain spotted fever (RMSF) among various regions of the American West during the early 20th century. We suggest that the wide variation in case fatality rates attributed to RMSF could have occurred by the inadvertent inclusion of cases of milder disease caused by R. parkeri Black Gap.

Evaluation of Gulf Coast Ticks (Acari: Ixodidae) for Ehrlichia and Anaplasma Species

Amblyomma maculatum Koch (the Gulf Coast tick) is an aggressive, human-biting ixodid tick distributed throughout much of the southeastern United States and is the primary vector for Rickettsia parkeri, an emerging human pathogen. Amblyomma maculatum has diverse host preferences that include white-tailed deer, a known reservoir for Ehrlichia and Anaplasma species, including the human pathogens E. ewingii and E. chaffeensis. To examine more closely the potential role of A. maculatum in the maintenance of various pathogenic Ehrlichia and Anaplasma species, we screened DNA samples from 493 questing adult A. maculatum collected from six U.S. states using broad-range Anaplasmataceae and Ehrlichia genus-specific PCR assays. Of the samples tested, four (0.8%) were positive for DNA of Ehrlichia ewingii, one (0.2%) was positive for Anaplasma platys, and one (0.2%) was positive for a previously unreported Ehrlichia species closely related to Ehrlichia muris and an uncultivated Ehrlichia species from Haemaphysalis longicornis ticks in Japan. No ticks contained DNA of Ehrlichia chaffeensis, Ehrlichia canis, the Panola Mountain Ehrlichia, or Anaplasma phagocytophilum. This is the first identification of E. ewingii, A. platys, and the novel Ehrlichia in questing Gulf Coast ticks; nonetheless the low prevalence of these agents suggests that A. maculatum is not likely an important vector of these zoonotic pathogens.

Development of a Rickettsia bellii-Specific TaqMan Assay Targeting the Citrate Synthase Gene

Rickettsia bellii is a rickettsial species of unknown pathogenicity that infects argasid and ixodid ticks throughout the Americas. Many molecular assays used to detect spotted fever group (SFG) Rickettsia species do not detect R. bellii, so that infection with this bacterium may be concealed in tick populations when assays are used that screen specifically for SFG rickettsiae. We describe the development and validation of a R. bellii-specific, quantitative, real-time PCR TaqMan assay that targets a segment of the citrate synthase (gltA) gene. The specificity of this assay was validated against a panel of DNA samples that included 26 species of Rickettsia, Orientia, Ehrlichia, Anaplasma, and Bartonella, five samples of tick and human DNA, and DNA from 20 isolates of R. bellii, including 11 from North America and nine from South America. A R. bellii control plasmid was constructed, and serial dilutions of the plasmid were used to determine the limit of detection of the assay to be one copy per 4 µl of template DNA. This assay can be used to better determine the role of R. bellii in the epidemiology of tick-borne rickettsioses in the Western Hemisphere.

Rickettsia amblyommatis sp. nov., a spotted fever group Rickettsia associated with multiple species of Amblyomma ticks in North, Central and South America

In 1973, investigators isolated a rickettsial organism, designated strain WB-8-2T, from an adult Amblyomma americanum tick collected at Land Between the Lakes National Recreation Area, TN, USA. This organism is now recognized as highly prevalent in A. americanum, as well as several other Amblyomma species found throughout the Western hemisphere. It has been suggested that cross-reactivity to WB-8-2T and similar strains contributes to the increasing number of spotted fever cases reported in the USA. In 1995, investigators provided preliminary evidence that this strain, as well as another strain from Missouri, represented a distinct taxonomic unit within the genus Rickettsia by evaluating sequences of the 16S rRNA and 17 kDa protein genes. However, the bacterium was never formally named, despite the use of the designation 'Rickettsia amblyommii' and later 'Candidatus Rickettsia amblyommii', for more than 20 years in the scientific literature. Herein, we provide additional molecular evidence to identify strain WB-8-2T as a representative strain of a unique rickettsial species and present a formal description for the species, with the proposed name modified to Rickettsia amblyommatis sp. nov. to conform to the International Code of Nomenclature of Prokaryotes. We also establish a pure culture of strain WB-8-2T and designate it as the type strain for the species. The type strain is WB-8-2T (=CRIRC RAM004T=CSURP2882T).

Co-Feeding Transmission of the Ehrlichia muris-Like Agent to Mice (Mus musculus)

The Ehrlichia muris-like agent (EMLA) is a newly recognized human pathogen found in Wisconsin and Minnesota. Ecological investigations have implicated both the blacklegged tick, Ixodes scapularis, and the white-footed mouse, Peromyscus leucopus, as playing roles in the maintenance of EMLA in nature. The work presented here shows that I. scapularis is an efficient vector of EMLA in a laboratory mouse model, but that Dermacentor variabilis, another frequent human biting tick found in EMLA endemic areas, is not. Additionally, I. scapularis larvae are able to acquire EMLA through co-feeding with infected nymphs. As EMLA only persists in mouse blood for a relatively short period of time, co-feeding transmission may play an important role in the maintenance of EMLA in ticks, and subsequently may play a role in limiting the geographic distribution of this pathogen in areas where co-feeding of larvae and nymphs is less common.

A real-time PCR assay for detection of the Ehrlichia muris-like agent, a newly recognized pathogen of humans in the upper Midwestern United States

The Ehrlichia muris-like agent (EMLA) is an emerging, tick-transmitted human pathogen that occurs in the upper Midwestern United States. Here, we describe the development and validation of a p13-based quantitative real-time PCR TaqMan assay to detect EMLA in blood or tissues of ticks, humans, and rodents. The primer and probe specificities of the assay were ascertained using a large panel of various Ehrlichia species and other members of Rickettsiales. In addition to control DNA, both non-infected and EMLA-infected human blood, Mus musculus blood, and M. musculus tissue extracts were evaluated, as were non-infected and EMLA-infected Ixodes scapularis and uninfected Dermacentor variabilis DNA lysates. The specificity of the probe was determined via real-time PCR. An EMLA p13 control plasmid was constructed, and serial dilutions were used to determine the analytical sensitivity, which was found to be 1 copy per 4μl of template DNA. The sensitivity and specificity of this assay provides a powerful tool for ecological studies involving arthropod vectors and their mammalian hosts.

Phylogeography of Rickettsia rickettsii genotypes associated with fatal Rocky Mountain spotted fever

Rocky Mountain spotted fever (RMSF), a tick-borne zoonosis caused by Rickettsia rickettsii, is among the deadliest of all infectious diseases. To identify the distribution of various genotypes of R. rickettsii associated with fatal RMSF, we applied molecular typing methods to samples of DNA extracted from formalin-fixed, paraffin-embedded tissue specimens obtained at autopsy from 103 case-patients from seven countries who died of RMSF. Complete sequences of one or more intergenic regions were amplified from tissues of 30 (29%) case-patients and revealed a distribution of genotypes consisting of four distinct clades, including the Hlp clade, regarded previously as a non-pathogenic strain of R. rickettsii. Distinct phylogeographic patterns were identified when composite case-patient and reference strain data were mapped to the state and country of origin. The phylogeography of R. rickettsii is likely determined by ecological and environmental factors that exist independently of the distribution of a particular tick vector.

Rickettsia felis in cat fleas, Ctenocephalides felis parasitizing opossums, San Bernardino County, California

Los Angeles and Orange Counties are known endemic areas for murine typhus in California; however, no recent reports of flea-borne rickettsioses are known from adjacent San Bernardino County. Sixty-five opossums (Didelphis virginiana) were trapped in the suburban residential and industrial zones of the southwestern part of San Bernardino County in 2007. Sixty out of 65 opossums were infested with fleas, primarily cat fleas, Ctenocephalides felis (Bouché, 1835). The flea minimum infection rate with Rickettsia felis was 13.3% in pooled samples and the prevalence was 23.7% in single fleas, with two gltA genotypes detected. In spite of historic records of murine typhus in this area, no evidence for circulation of R. typhi in fleas was found during the present study. Factors contributing to the absence of R. typhi in these cat fleas in contrast to its presence in cat fleas from Orange and Los Angeles Counties are unknown and need to be investigated further in San Bernardino County.

Rickettsia rickettsii in Rhipicephalus ticks, Mexicali, Mexico

Circulation of a unique genetic type of Rickettsia rickettsii in ticks of the Rhipicephalus sanguineus complex was detected in Mexicali, Baja California, Mexico. The Mexican R. rickettsii differed from all isolates previously characterized from the endemic regions of Rocky Mountain spotted fever in northern, central, and southern Americas. Rhipicephalus ticks in Mexicali are genetically different from Rh. sanguineus found in the United States.

Detection and identification of rickettsial agents in ticks from domestic mammals in eastern Panama

Several outbreaks of Rocky Mountain spotted fever have occurred in recent years in Colombian communities close to the border with Panama. However, little is known about rickettsiae and rickettsial diseases in eastern Panamanian provinces, the Darien Province and the Kuna Yala, located north of the endemic area in Colombia. In 2007, 289 ticks were collected in several towns from dogs, horses, mules, cows, and pigs. DNA was extracted from 124 Dermacentor nitens, 64 Rhipicephalus sanguineus, 43 Amblyomma ovale, 35 A. cajennense, 10 Boophilus microplus, 4 A. oblongoguttatum, and 9 A. cajennense nymphs. SYBR-Green polymerase chain reaction assays targeting a fragment of the OmpA and 16S rRNA genes were used for detection of DNA of the spotted fever group rickettsiae (SFGR) and Anaplasmataceae (Anaplasma and Ehrlichia), respectively. In total, 37.4% ticks were positive for SFGR, including 20.3% R. sanguineus, 27.9% A. ovale, 25.8% D. nitens, 50% B. microplus, 50% A. oblongoguttatum, and 100% A. cajennense. The presence of Rickettsia amblyommii DNA was confirmed by sequencing in A. cajennense, A. oblongoguttatum, A. ovale, B. microplus, and R. sanguineus. DNA of R. rickettsii was only detected in one D. nitens collected from a horse in Santa Fe, Darien Province. Prevalence of Anaplasmataceae varied from 6.3% in R. sanguineus to 26.5% in A. cajennense. DNA of Ehrlichia chaffensis was found in three D. nitens and three A. cajennense from horses. This is the first study providing molecular characterization and prevalence information on SFGR in ticks from these areas and thus will be helpful for future evaluations of the risk of rickettsial diseases for individuals living in this region.

Rickettsia typhi and R. felis in rat fleas (Xenopsylla cheopis), Oahu, Hawaii

Rickettsia typhi (prevalence 1.9%) and R. felis (prevalence 24.8%) DNA were detected in rat fleas (Xenopsylla cheopis) collected from mice on Oahu Island, Hawaii. The low prevalence of R. typhi on Oahu suggests that R. felis may be a more common cause of rickettsiosis than R. typhi in Hawaii.

Genome sequence of Fusobacterium nucleatum subspecies polymorphum - a genetically tractable fusobacterium

Fusobacterium nucleatum is a prominent member of the oral microbiota and is a common cause of human infection. F. nucleatum includes five subspecies: polymorphum, nucleatum, vincentii, fusiforme, and animalis. F. nucleatum subsp. polymorphum ATCC 10953 has been well characterized phenotypically and, in contrast to previously sequenced strains, is amenable to gene transfer. We sequenced and annotated the 2,429,698 bp genome of F. nucleatum subsp. polymorphum ATCC 10953. Plasmid pFN3 from the strain was also sequenced and analyzed. When compared to the other two available fusobacterial genomes (F. nucleatum subsp. nucleatum, and F. nucleatum subsp. vincentii) 627 open reading frames unique to F. nucleatum subsp. polymorphum ATCC 10953 were identified. A large percentage of these mapped within one of 28 regions or islands containing five or more genes. Seventeen percent of the clustered proteins that demonstrated similarity were most similar to proteins from the clostridia, with others being most similar to proteins from other gram-positive organisms such as Bacillus and Streptococcus. A ten kilobase region homologous to the Salmonella typhimurium propanediol utilization locus was identified, as was a prophage and integrated conjugal plasmid. The genome contains five composite ribozyme/transposons, similar to the CdISt IStrons described in Clostridium difficile. IStrons are not present in the other fusobacterial genomes. These findings indicate that F. nucleatum subsp. polymorphum is proficient at horizontal gene transfer and that exchange with the Firmicutes, particularly the Clostridia, is common.

Molecular typing of isolates of Rickettsia rickettsii by use of DNA sequencing of variable intergenic regions

Rickettsia rickettsii, the causative agent of Rocky Mountain spotted fever, is found throughout the Americas, where it is associated with different animal reservoirs and tick vectors. No molecular typing system currently exists to allow for the robust differentiation of isolates of R. rickettsii. Analysis of eight completed genome sequences of rickettsial species revealed a high degree of sequence conservation within the coding regions of chromosomes in the genus. Intergenic regions between coding sequences should be under less selective pressure to maintain this conservation and thus should exhibit greater nucleotide polymorphisms. Utilizing these polymorphisms, we developed a molecular typing system that allows for the genetic differentiation of isolates of R. rickettsii. This typing system was applied to a collection of 38 different isolates collected from humans, animals, and tick vectors from different geographic locations. Serotypes 364D, from Dermacentor occidentalis ticks, and Hlp, from Haemaphysalis leporispalustris ticks, appear to be distinct genotypes that may not belong to the species R. rickettsii. We were also able to differentiate 36 historical isolates of R. rickettsii into three different phylogenetic clades containing seven different genotypes. This differentiation correlated well, but not perfectly, with the geographic origin and likely tick vectors associated with the isolates. The few apparent typing discrepancies found suggest that the molecular ecology of R. rickettsii needs more investigation.

Chromosome rearrangement and diversification of Francisella tularensis revealed by the type B (OSU18) genome sequence

The gamma-proteobacterium Francisella tularensis is one of the most infectious human pathogens, and the highly virulent organism F. tularensis subsp. tularensis (type A) and less virulent organism F. tularensis subsp. holarctica (type B) are most commonly associated with significant disease in humans and animals. Here we report the complete genome sequence and annotation for a low-passage type B strain (OSU18) isolated from a dead beaver found near Red Rock, Okla., in 1978. A comparison of the F. tularensis subsp. holarctica sequence with that of F. tularensis subsp. tularensis strain Schu4 (P. Larsson et al., Nat. Genet. 37:153-159, 2005) highlighted genetic differences that may underlie different pathogenicity phenotypes and the evolutionary relationship between type A and type B strains. Despite extensive DNA sequence identity, the most significant difference between type A and type B isolates is the striking amount of genomic rearrangement that exists between the strains. All but two rearrangements can be attributed to homologous recombination occurring between two prominent insertion elements, ISFtu1 and ISFtu2. Numerous pseudogenes have been found in the genomes and are likely contributors to the difference in virulence between the strains. In contrast, no rearrangements have been observed between the OSU18 genome and the genome of the type B live vaccine strain (LVS), and only 448 polymorphisms have been found within non-transposase-coding sequences whose homologs are intact in OSU18. Nonconservative differences between the two strains likely include the LVS attenuating mutation(s).

Complete genome sequence of Rickettsia typhi and comparison with sequences of other rickettsiae

Rickettsia typhi, the causative agent of murine typhus, is an obligate intracellular bacterium with a life cycle involving both vertebrate and invertebrate hosts. Here we present the complete genome sequence of R. typhi (1,111,496 bp) and compare it to the two published rickettsial genome sequences: R. prowazekii and R. conorii. We identified 877 genes in R. typhi encoding 3 rRNAs, 33 tRNAs, 3 noncoding RNAs, and 838 proteins, 3 of which are frameshifts. In addition, we discovered more than 40 pseudogenes, including the entire cytochrome c oxidase system. The three rickettsial genomes share 775 genes: 23 are found only in R. prowazekii and R. typhi, 15 are found only in R. conorii and R. typhi, and 24 are unique to R. typhi. Although most of the genes are colinear, there is a 35-kb inversion in gene order, which is close to the replication terminus, in R. typhi, compared to R. prowazekii and R. conorii. In addition, we found a 124-kb R. typhi-specific inversion, starting 19 kb from the origin of replication, compared to R. prowazekii and R. conorii. Inversions in this region are also seen in the unpublished genome sequences of R. sibirica and R. rickettsii, indicating that this region is a hot spot for rearrangements. Genome comparisons also revealed a 12-kb insertion in the R. prowazekii genome, relative to R. typhi and R. conorii, which appears to have occurred after the typhus (R. prowazekii and R. typhi) and spotted fever (R. conorii) groups diverged. The three-way comparison allowed further in silico analysis of the SpoT split genes, leading us to propose that the stringent response system is still functional in these rickettsiae.

Colicins produced by the Escherichia fergusonii strains closely resemble colicins encoded by Escherichia coli

Plasmid DNA of six Escherichia fergusonii colicinogenic strains (three producers of colicin E1, two of Ib and one of Ia) was isolated and the colicin-encoding regions of the corresponding Col plasmids were sequenced. Two new variants of colicin E1, one of colicin Ib, and one of colicin Ia were identified as well as new variants of the colicin E1 and colicin Ib immunity proteins and the colicin E1 lysis polypeptide. The recombinant Escherichia coli producer harboring pColE1 from E. fergusonii strain EF36 (pColE1-EF36) was found to be only partially immune to E1 colicins produced by two other E. fergusonii strains suggesting that pColE1-EF36 may represent an ancestor ColE1 plasmid.