Novel Rickettsia and host records for argasid ticks, including Alveonasus cooleyi, on wild mammals in Baja California, Mexico.

We conducted surveillance of mammals to investigate their associations with argasid ticks and tick-borne pathogens. During 2021, a total of 20 wild carnivores and 57 lagomorphs were sampled, and 39 argasid ticks belonging to two species were collected. All mammals and ticks were tested by molecular assays to detect Borrelia and Rickettsia infections. Nine ticks identified as Otobius megnini were collected from two coyotes (Canis latrans) and 30 Alveonasus cooleyi (McIvor 1941) were collected from six bobcats (Lynx rufus) and one rabbit (Sylvilagus auduboni). We detected Rickettsia spp. DNA in 21 of the 27 (77.8%) tested Av. cooleyi and none of the O. megnini. No ticks were PCR-positive for borreliae and all mammals were PCR-negative for both pathogen genera. Phylogenetic analysis based on gltA, htrA, and 16 S rRNA targets revealed that all rickettsiae from Av. cooleyi clustered with ancestral group rickettsiae, likely representing a novel species of possibly endosymbiotic Rickettsia. The significance of Av. cooleyi and the newly identified Rickettsia sp. to the health of wildlife is unknown, and further work is indicated to determine whether they may be relevant to public health or carnivore conservation.

Spatial distribution patterns of tick community structure in sympatric jaguars (Panthera onca) and pumas (Puma concolor) from three ecoregions in Mexico.

We examined tick communities on wild felid hosts in three ecoregions of Mexico. We collected 186 ticks of 7 species from 10 pumas (Puma concolor) and 9 jaguars (Panthera onca). Tick community composition varied across the ecoregions, and across host species within each region. Overall, Ixodes affinis, Amblyomma ovale, and Amblyomma tenellum were the most abundant species; however, only the latter two ticks were distributed across all three ecoregions, while I. affinis, along with Ixodes spinipalpis, Amblyomma inornatum, and Amblyomma parvum were restricted to more limited geographical regions. Ixodes affinis occurred strictly in southern tropical rainforest ecoregions and was significantly more abundant in Selva Lacandona compared with the Yucatán Peninsula. Amblyomma ovale was significantly more common in the tropical dry forest in the Pacific coastal ecoregion. Amblyomma tenellum abundance tended to be higher on jaguars, while I. affinis abundance was higher on pumas. Regional distribution patterns of some tick species (e.g., I. affinis and I. spinipalpis) may be determined by off-host environmental conditions rather than host factors. In contrast, at the local scale, occurrence and abundance of some tick species (e.g., A. tenellum, A. ovale and Rhipicephalus microplus) might be driven by ecological-host factors, such as habitat use or predator-prey relationships.

A compartment and metapopulation model of Rocky Mountain spotted fever in southwestern United States and northern Mexico.

Rocky Mountain spotted fever (RMSF) is a fatal tick-borne zoonotic disease that has emerged as an epidemic in western North America since the turn of the 21st century. Along the US south-western border and across northern Mexico, the brown dog tick, Rhipicephalus sanguineus, is responsible for spreading the disease between dogs and humans. The widespread nature of the disease and the ongoing epidemics contrast with historically sporadic patterns of the disease. Because dogs are amplifying hosts for the Rickettsia rickettsii bacteria, transmission dynamics between dogs and ticks are critical for understanding the epidemic. In this paper, we developed a compartment metapopulation model and used it to explore the dynamics and drivers of RMSF in dogs and brown dog ticks in a theoretical region in western North America. We discovered that there is an extended lag-as much as two years-between introduction of the pathogen to a naïve population and epidemic-level transmission, suggesting that infected ticks could disseminate extensively before disease is detected. A single large city-size population of dogs was sufficient to maintain the disease over a decade and serve as a source for disease in surrounding smaller towns. This model is a novel tool that can be used to identify high risk areas and key intervention points for epidemic RMSF spread by brown dog ticks.

The emergence of Rocky Mountain spotted fever in the southwestern United States and northern Mexico requires a binational One Health approach.

Rocky Mountain spotted fever (RMSF) is an international and quintessential One Health problem. This paper synthesizes recent knowledge in One Health, binational RMSF concerns, and veterinary and human medical perspectives to this fatal, reemerging problem. RMSF, a life-threatening tick-borne disease caused by the bacterium Rickettsia rickettsii, emerged during the first decade of the 21st century in impoverished communities in the southwestern US and northern Mexico. Lack of an index of suspicion, delay in diagnosis, and delayed initiation of antibiotic treatment contribute to fatality. Campaigns targeting dog neutering, restraint to residents' properties, and on-dog and on-premises treatment with acaricides temporarily reduce prevalence but are often untenable economically. Contemporary Mexican RMSF is hyperendemic in small communities and cities, whereas epidemics occur in the western US primarily in small tribal communities. In in both locations, the epidemics are fueled by free-roaming dogs and massive brown dog tick populations. In the US, RMSF has a case fatality rate of 5% to 7%; among thousands of annual cases in Mexico, case fatality often exceeds 30%.1,2 Numerous case patients in US border states have recent travel histories to northern Mexico. Veterinarians and physicians should alert the public to RMSF risk, methods of prevention, and the importance of urgent treatment with doxycycline if symptomatic. One Health professionals contribute ideas to manage ticks and rickettsial disease and provide broad education for the public and medical professionals. Novel management approaches include vaccine development and deployment, acaricide resistance monitoring, and modeling to guide targeted dog population management and other interventions.

Roaming Dogs, Intense Brown Dog Tick Infestation, and Emerging Rocky Mountain Spotted Fever in Tijuana, México.

A two decades-long epidemic of Rocky Mountain spotted fever in northern México reached the U.S. border city of Tijuana in 2021. Cases were near the city periphery in marginalized areas, some lacking infrastructure such as streets or utilities. We worked in the three census areas where human cases were reported and in 12 additional control Áreas Geoestadisticas Básicas. There were dogs, the primary tick host and Rickettsia rickettsii reservoir, in 76% of homes, with 2.2 owned dogs per home on average, approximately equal numbers of roaming dogs were seen, and 46.2% of owned dogs were allowed to roam in the street. Sixty-eight percent of people had heard of Rocky Mountain spotted fever (RMSF), and 35% self-reported tick infestation, including 19% of homes without dogs. Ticks appeared to move among houses of adjacent neighbors. Of 191 examined dogs, 61.8% were tick-infested, with 6-fold increased odds if they were allowed to roam. Although no dogs were Rickettsia polymerase chain reaction-positive, we found one R. rickettsii- and 11 Rickettsia massiliae-infected ticks. The rickettsial IgG seroprevalence by immunofluorescence antibody assay was 76.4%, associated with unhealthy body condition, adults, dogs with >10 ticks, more dogs being seen in the area, and dogs being permitted in the street. Insufficient medical and canine management resources have contributed to a case fatality rate of RMSF that has exceeded 50% in areas. High canine seroprevalence suggests risks to people and dogs; unfortunately, herd immunity is impeded by high turnover in the canine population owing to the birth of puppies and high death rates. Binational One Health workers should monitor disease spread, enact canine population management and tick eradication, and provide prevention, diagnostic, and treatment support.

A mutation associated with resistance to synthetic pyrethroids is widespread in US populations of the tropical lineage of Rhipicephalus sanguineus s.l.

The brown dog tick, Rhipicephalus sanguineus sensu lato (s.l.), is an important vector for Rickettsia rickettsii, causative agent of Rocky Mountain spotted fever. Current public health prevention and control efforts to protect people involve preventing tick infestations on domestic animals and in and around houses. Primary prevention tools rely on acaricides, often synthetic pyrethroids (SPs); resistance to this chemical class is widespread in ticks and other arthropods. Rhipicephalus sanguineus s.l. is a complex that likely contains multiple unique species and although the distribution of this complex is global, there are differences in morphology, ecology, and perhaps vector competence among these major lineages. Two major lineages within Rh. sanguineus s.l., commonly referred to as temperate and tropical, have been documented from multiple locations in North America, but are thought to occupy different ecological niches. To evaluate potential acaricide resistance and better define the distributions of the tropical and temperate lineages throughout the US and in northern Mexico, we employed a highly multiplexed amplicon sequencing approach to characterize sequence diversity at: 1) three loci within the voltage-gated sodium channel (VGSC) gene, which contains numerous genetic mutations associated with resistance to SPs; 2) a region of the gamma-aminobutyric acid-gated chloride channel gene (GABA-Cl) containing several mutations associated with dieldrin/fipronil resistance in other species; and 3) three mitochondrial genes (COI, 12S, and 16S). We utilized a geographically diverse set of Rh sanguineus s.l. collected from domestic pets in the US in 2013 and a smaller set of ticks collected from canines in Baja California, Mexico in 2021. We determined that a single nucleotide polymorphism (T2134C) in domain III segment 6 of the VGSC, which has previously been associated with SP resistance in Rh. sanguineus s.l., was widespread and abundant in tropical lineage ticks (>50 %) but absent from the temperate lineage, suggesting that resistance to SPs may be common in the tropical lineage. We found evidence of multiple copies of GABA-Cl in ticks from both lineages, with some copies containing mutations associated with fipronil resistance in other species, but the effects of these patterns on fipronil resistance in Rh. sanguineus s.l. are currently unknown. The tropical lineage was abundant and geographically widespread, accounting for 79 % of analyzed ticks and present at 13/14 collection sites. The temperate and tropical lineages co-occurred in four US states, and as far north as New York. None of the ticks we examined were positive for Rickettsia rickettsii or Rickettsia massiliae.

POTENTIAL SHARED DISEASE RISK AMONG DOGS AND COYOTES (CANIS LATRANS) EXEMPLIFIED BY THE ECOLOGY OF RICKETTSIOSIS IN A ROCKY MOUNTAIN SPOTTED FEVER-EPIDEMIC REGION IN NORTHERN MEXICO.

Rocky Mountain spotted fever (RMSF), caused by the bacterium Rickettsia rickettsii, is a re-emerging tick-borne zoonosis in North America, with hundreds of human fatalities in multiple outbreaks in northern Mexico and the southwestern US in the past few decades. Free-roaming dogs are key because they are reservoirs for the pathogen and the main hosts of the brown dog tick (Rhipicephalus sanguineus), which vectors RMSF in this region. Because coyotes (Canis latrans) can be infected with R. rickettsii and infested with Rh. sanguineus, we hypothesized that space sharing among dogs and coyotes could enhance disease risks. In summer 2021, we captured and sampled 11 coyotes at two sites in Baja California, Mexico, near population centers with human cases of RMSF, and fitted seven individuals with GPS logging collars. We also tested tissue samples, sera, and ectoparasites for DNA of R. rickettsii with PCR and used serology to detect antibodies to R. rickettsii. Finally, we deployed an array of cameras to document dog-coyote interactions. Mean home range size was 40.37 km2. Both GPS and camera data showed considerable home range overlap both between individual coyotes and between coyotes and dogs. Coyotes were active in areas where dogs occur including the domestic interface surrounding human settlements. Although none of our samples were positive for R. rickettsii on PCR, 72.7% (8/11) of the samples were seropositive with titers ≥64. Our data confirm shared space use and risk of shared parasites and disease between coyotes and dogs.

Rickettsial antibodies and Rickettsia bellii detection in lagomorphs and their ectoparasites in Northern Baja California, Mexico.

Lagomorphs-principally rabbits and hares-have been implicated as hosts for vectors and reservoirs for pathogens associated with multiple rickettsial diseases. Western North America is home to diverse rickettsial pathogens which circulate among multiple wild and domestic hosts and tick and flea vectors. The purpose of this study was to assess lagomorphs and their ectoparasites in 2 locations in northern Baja California, Mexico, for exposure to and infection with rickettsial organisms. In total, 55 desert cottontail rabbits (Sylvilagus audubonii) (Baird) and 2 black-tailed jackrabbits (Lepus californicus) (Gray) were captured. In Mexicali, ticks were collected from 44% (14/32) of individuals, and were exclusively Haemaphysalis leporispalustrisNeumann (Acari: Ixodidae); in Ensenada, ticks were collected from 70% (16/23) individuals, and 95% were Dermacentor parumapertus. Euhoplopsyllus glacialis affinisBaker (Siphonaptera: Pulicidae) fleas were collected from 72% of rabbits and 1 jackrabbit from Mexicali, while the few fleas found on hosts in Ensenada were Echidnophaga gallinaceaWestwood (Siphonaptera: Pulicidae) and Cediopsylla inaequalis(Siphonaptera: Pulicidae). Rickettsia bellii was the only rickettsial organism detected and was identified in 88% of D. parumapertus and 67% of H. leporispalustris ticks from Ensenada. A single tissue sample from a jackrabbit was positive for R. belli (Rickettsiales: Rickettsiaceae). Hosts in Ensenada had a significantly higher prevalence of rickettsial antibodies than hosts in Mexicali (52.3% vs. 21.4%). Although R. bellii is not regarded as pathogenic in humans or other mammals, it may contribute to immunity to other rickettsiae. The marked difference in distribution of ticks, fleas, and rickettsial exposure between the 2 locations suggests that disease transmission risk may vary markedly between communities within the same region.

Will new ticks invade North America? How to identify future invaders.

Invasive tick species and the pathogens they transmit pose increasing threats to human and animal health around the world. Little attention has been paid to the characteristics enabling tick species to invade. Here we analyze examples of tick invasion events in North America to identify factors that facilitated the invasion. Commonalities among invasive ticks are that they thrive in anthropogenically modified habitats, feed on either domestic animals or wildlife occurring in high density, and can survive across a broad range of climatic conditions. Invasive tick species varied widely in life history and reproductive habits, suggesting that invasion occurs when multiple characteristics converge. The combination of potential characteristics leading to invasion, however, improves our ability to predict future invaders and inform surveillance.

Tick-borne pathogens detected in sheltered dogs during an epidemic of Rocky Mountain spotted fever, a One Health challenge.

OBJECTIVE: To assess exposure to and infection with 3 pathogens (Rickettsia rickettsii, Anaplasma platys, and Ehrlichia canis) vectored by brown dog ticks (Rhipicephalus sanguineus) in sheltered dogs at the western US-Mexico border. ANIMALS: 239 dogs in shelters in San Diego and Imperial counties, US, and Mexicali and Tijuana, Mexico. PROCEDURES: Each dog had blood drawn and basic demographic data collected. PCR was performed to determine active infection with Rickettsia spp, E canis, and A platys. Serology was performed to determine exposure to Rickettsia, Anaplasma, and Ehrlichia species. RESULTS: 2 of 78 (2.6%) dogs sampled in Tijuana were actively infected with R rickettsii. A single brown dog tick collected from a dog in Tijuana was PCR-positive for R rickettsii. Infection with E canis and A platys ranged across shelters from 0% to 27% and 0% to 33%, respectively. Dogs in all 4 locations demonstrated exposure to all 3 pathogens, though Rickettsia and Ehrlichia seropositivity was highest in Mexicali (81% and 49%, respectively) and Anaplasma seropositivity was highest in Tijuana (45%). CLINICAL RELEVANCE: While infection and exposure were highest in sheltered dogs in the southern locations, dogs in all locations demonstrated exposure to all pathogens, demonstrating the potential for emergence and spread of zoonotic pathogens with significant public health consequences in southern California and northern Baja California. In addition, veterinarians and shelter staff should be aware that Ehrlichia or Anaplasma infection may co-occur with Rocky Mountain spotted fever, which is a human health risk.

A new species of tick, Ixodes (Ixodes) mojavensis (Acari: Ixodidae), from the Amargosa Valley of California.

Ixodes (Ixodes) mojavensis, n. sp. (Acari: Ixodidae), is described from all parasitic stages collected from the endangered vole Microtus californicus scirpensis Bailey, 1900 (Rodentia: Cricetidae), Mus musculus L. 1758 (Rodentia: Muridae), and Reithrodontomys megalotis (Baird; 1857) (Rodentia: Cricetidae) in the Amargosa Valley of California. When first collected in 2014, this tick was tentatively identified as Ixodes minor Neumann, 1902 because the nucleotide similarity between its 16S rDNA sequence and a homologous GenBank sequence from an I. minor from the eastern U.S. was 99.51%. Nevertheless, adults of I. mojavensis differ morphologically from I. minor by hypostomal dentition, absence of a spur on palpal segment I, and punctation patterns; nymphs by the shapes of basis capituli, auriculae, cervical grooves and external files of hypostomal denticles; and larvae by the length of idiosomal setae and hypostomal dentition. DNA sequencing of fragments of 4 different genes, 12S rDNA, 16S rDNA, cytochrome c oxidase subunit I (COI), and intergenic transcribed spacer 2 (ITS2) of I. mojavensis and of closely related species of Ixodes shows that the mitochondrial gene sequences of the new tick species are almost identical to the I. minor homologous genes. Phylogenetically, the two species do not cluster in mutually exclusive monophyletic clades. However, ITS2 sequences of I. mojavensis and I. minor diverge deeply (≥ 5.74% maximum likelihood divergence) and are as different as homologous genes from other recognized species. The discrepancy between the two sets of genes is suggestive of past mitochondrial introgression or incomplete mitochondrial lineage sorting.

Host species and environment drivers of ectoparasite community of rodents in a Mojave Desert wetlands.

Drivers of patterns of ectoparasitism in rodents in patchy Mojave Desert wetlands were investigated. A total of 1,571 ectoparasites in Mesostigmata, Trombidiformes, Siphonaptera and Ixodida were collected from 341 rodents (Microtus californicus scirpensis, Mus musculus, Reithrodontomys megalotis, Peromyscus eremicus, and Neotoma lepida) at eleven marshes. Trombiculids accounted for 82.5% of mites, followed by the mesostigmatid Ornithonyssus bacoti (17.5%), with chiggers predominating on voles and harvest mice. There were at least three genera of chiggers (Eutrombicula alfreddugesi, Euschoengastia sp. novel, and Blankaartia sp. novel). Fleas included Orchopeas leucopus (90.3% of all fleas) and O. sexdentatus (9.7%), and ticks were the novel endemic Ixodes mojavensis (82.1% of ticks) and Dermacentor similis (17.9%). On all hosts and at all marshes, coverage-based rarefaction sampling was over 96%, indicating coverage sufficient for analysis. Dissimilarities in ectoparasite community structure were driven mainly by chiggers, I. mojavensis and O. leucopus. Northern marshes were dominated by chiggers; central marshes by I. mojavensis; and southern marshes by O. leucopus. Primary determinants of ectoparasite community structure were host species, patch size, and parasite interspecific interactions. Host species richness and environmental factors such as patch distance and water and plant availability were not significantly associated with patterns of ectoparasitism. There were nine (60%) significant negative pairwise associations between ectoparasite taxa and no significant positive relationships. Ixodes mojavensis had the highest number of negative associations (with five other species), followed by chiggers and O. bacoti with two negative associations each. The study area is among the most arid in North America and supports numerous rare and endemic species in increasingly isolated wetland habitat patches; knowledge of ectoparasite ecology in this region identifies potential ectoparasite vectors, and provides information needed to design and implement programs to manage vector-borne diseases for purposes of wildlife conservation.

Effect of Temperature on Host Preference in Two Lineages of the Brown Dog Tick, Rhipicephalus sanguineus.

Rhipicephalus sanguineus is a species complex of ticks that vector disease worldwide. Feeding primarily on dogs, members of the complex also feed incidentally on humans, potentially transmitting disease agents such as Rickettsia rickettsii, Rickettsia conorii, and Ehrlichia species. There are two genetic Rh. sanguineus lineages in North America, designated as the temperate and tropical lineages, which had occurred in discrete locations, although there is now range overlap in parts of California and Arizona. Rh. sanguineus in Europe are reportedly more aggressive toward humans during hot weather, increasing the risk of pathogen transmission to humans. The aim of this study was to assess the impact of hot weather on choice between humans and dog hosts among tropical and temperate lineage Rh. sanguineus individuals. Ticks in a two-choice olfactometer migrated toward a dog or human in trials at room (23.5°C) or high temperature (38°C). At 38°C, 2.5 times more tropical lineage adults chose humans compared with room temperature, whereas temperate lineage adults demonstrated a 66% reduction in preference for dogs and a slight increase in preference for humans. Fewer nymphs chose either host at 38°C than at room temperature in both lineages. These results demonstrate that risk of disease transmission to humans may be increased during periods of hot weather, where either lineage is present, and that hot weather events associated with climatic change may result in more frequent rickettsial disease outbreaks.

West Nile Virus in Hummingbirds in California, USA, 2005-17.

Although West Nile virus (WNV) infects many avian species, the prevalence and impact of WNV in hummingbirds (Family Trochilidae) have not been described. We focused on hummingbird mortality and WNV infection using data from the state of California's Dead Bird Surveillance Program for the years 2005-17. The overall prevalence of WNV in tested carcasses was 10.1% (49/486), with annual prevalence ranging from 0-28%. Prevalence by county ranged from 0-40% while prevalence by species ranged from 0-12%. We demonstrated that hummingbirds were naturally infected with WNV and displayed temporal and spatial patterns of infection consistent with trends observed in other avian species.