Using metagenomic sequencing, we identified a patient infected with Rickettsia lanei who was initially diagnosed with Rocky Mountain spotted fever (RMSF), a clinically similar disease caused by infection with R. rickettsii. Our investigation highlights the importance of clinical, epidemiologic, and laboratory partnerships to leverage the discovery of novel pathogens.

Dermacentor parumapertus Neumann is an ixodid tick distributed broadly across arid and semi-arid regions of the western United States and northern Mexico. D. parumapertus has garnered little attention by most medical entomologists due predominantly to historical assumptions that it fed almost exclusively on lagomorphs. We summarized data from multiple sources to provide a comprehensive and current description of the distribution, host records, and Rickettsia species associated with this understudied species of potential medical importance. By using historical and recent scientific literature, natural history museum records, and archival collection records from the US National Tick Collection and the US Department of Agriculture (USDA)-National Veterinary Services Laboratories, we compiled county- and municipality-level locality records for D. parumapertus from 119 counties in 14 US states, and 12 municipalities in 10 states in Mexico. We further identified host records for nymphs and adults of D. parumapertus from 52 vertebrate species. From 199 field-collected adult D. parumapertus, we detected DNA of Rickettsia bellii, Rickettsia rhipicephali, and the potentially pathogenic Rickettsia parkeri Black Gap genotype in 61.3%, 4.5%, and 4.0% of the total specimens, respectively. From these data and information acquired from historical and recent scientific literature, we identified the occurrence of R. parkeri-infected D. parumapertus from 10 counties in 6 US states, and 2 municipalities in 2 states in Mexico. Collectively, these findings indicate broad distribution of D. parumapertus in western North America, a broader range of hosts than summarized previously, and association of this tick with a potential pathogen in several US states and municipalities of Mexico.

Rocky Mountain spotted fever (RMSF) is a deadly tick-borne disease caused by the bacterium Rickettsia rickettsii. An ongoing epidemic of RMSF is affecting tribal communities in Arizona, with nearly 500 cases and 28 deaths since 2003. The San Carlos Apache Tribe has been consistently working to prevent RMSF using tick collars on dogs, pesticide treatments around homes, and increasing education for nearly a decade. Besides monitoring human disease levels and tick burden on dogs, we have little understanding of the long-term impact of prevention practices on tick abundance and infection rates in the peridomestic environment. We evaluated risk factors associated for tick infestation at home sites across the San Carlos Indian Reservation as well as R. rickettsii and Rickettsia massiliae prevalence in off-host ticks. Although the presence of fencing appears protective, the number of nearby structures is the most important risk factor associated with increased adult and nymphal tick abundance, highlighting the impact of a free-roaming dog population.

RMSF, a tickborne infection caused by Rickettsia rickettsii, produces severe and fatal disease in humans and dogs. Since the beginning of the 21st century, cases have risen dramatically, most notably in Mexico and Brazil, where outbreaks occur in urban centers including cities with populations of > 1,000,000 persons. Reported case fatality rates can exceed 50%. Factors consistent with high case fatality include lack of awareness of disease ecology, limited capacity for diagnosis, and delay in appropriate antimicrobial treatment. The emergence of urban hyperendemic foci has been leveraged by 2 distinct but similar anthropogenic events that create disproportionately high numbers of vertebrate amplifiers of R rickettsii, as well as the tick species that transmit this pathogen in proximity with dense human populations. This often occurs in neighborhoods with a highly marginalized at-risk population that includes persons in poverty and particularly children, and health management systems that are under-resourced. We discuss strategies to reduce host dog populations, particularly in Mexico, and capybaras in Brazil. We review challenges to the control of tick populations in these settings. Robust systems are required to enhance awareness of RMSF among medical practitioners and people at risk of RMSF. Public health campaigns should incorporate innovative behavioral science (eg, diverse learning models, motivational interviews, and gamification) to increase prevention and understanding within communities. While anti-Rickettsia or anti-tick vaccines will be necessary to resolve this One Health crisis, impactful implementation will require data-driven and multiple-target innovations to address challenges with hosts, ticks, medical systems, and public welfare. The companion Currents in One Health by Foley, Backus, and L & oacute;pez-P & eacute;rez, JAVMA, March 2025, addresses helpful information for the practicing veterinarian.

Haemaphysalis leporispalustris (the rabbit tick) is one of the most broadly distributed hard tick species in the Americas. In 2018, investigators amplified DNA from a spotted fever group Rickettsia (SFGR) species found in host-seeking larvae and nymphs of H. leporispalustris collected in northern California and proposed the name Candidatus "Rickettsia lanei" using results obtained via multilocus sequence typing. Several years later, other investigators reported the amplification of DNA from the blood of two severely ill patients in northern California that demonstrated near-identical sequences with several gene sequences of Ca. "R. lanei," suggesting that this SFGR is pathogenic to humans. Recently, nearly complete genetic identity was identified between segments of the outer membrane protein A gene of Ca. "R. lanei" and an otherwise unidentified SFGR isolate designated as HLP 7421, which was established in 1961 from H. leporispalustris collected in the Bitterroot Valley of western Montana. Herein, the results of whole-genome sequencing of HLP 7421 are reported, revealing a 1,270,740 base pair chromosome most similar to that of Rickettsia rickettsii subsp. californica, the etiologic agent of Pacific Coast tick fever. Digital DNA-DNA hybridization and orthologous average nucleotide identity percentages between HLP 7421 and several closely related SFGR species meet the criteria for species identification using one genome-based algorithm for defining taxa in the Rickettsia genus. The name Rickettsia lanei is proposed for this pathogen, and its potential contribution to the evolving mosaic of tick-borne spotted fevers in the Americas is discussed.

Pacific Coast tick fever is a recently described zoonotic disease in California caused by a spotted fever group rickettsia, Rickettsia rickettsii subsp. californica (formerly Rickettsia 364D) and transmitted by the Pacific Coast tick, Dermacentor occidentalis. Like many emerging vector-borne diseases, knowledge regarding the transmission cycle, contribution from potential amplifying hosts, and geographic distribution of R. rickettsii californica is limited. We paired molecular analysis with comparative spatial niche modeling to identify vertebrate hosts potentially involved in the transmission cycle of this pathogen. We identified R. rickettsii californica DNA in three mammal species (Otospermophilus beecheyi, Lepus californicus, and Sylvilagus audubonii). This is the first record of R. rickettsii californica detected in mammals and may indicate potential amplifying hosts for this human pathogen. Species niche modeling of uninfected and infected D. occidentalis identified areas of high suitability along the coast and Sierra Nevada foothills of California. These findings support the hypothesis that amplifying host(s) may support higher infection prevalence in the infected tick regions compared to other parts of the tick's range. Potential host species distribution models (SDMs) were constructed from museum records and niche overlap statistics were used to compare habitat suitability with R. rickettsii californica-infected tick SDMs. We found higher than null overlap of infected ticks with California ground squirrels (O. beecheyii) and trending, but nonsignificant, overlap with two lagomorph species. Pairing molecular and niche modeling may be a useful approach to identify species that are involved in the maintenance of emerging tick-borne zoonoses.

ABSTRACT Mycoplasma (Class: Mollicutes) contamination in cell cultures is a universal concern for research laboratories. Some estimates report contamination in up to 35% of continuous cell lines. Various commercial antibiotic treatments can successfully decontaminate clean cell lines in vitro ; however, in vitro decontamination of bacterial cultures remains challenging. Intracellular bacteria like those in the genera Rickettsia and Ehrlichia require cell culture for primary isolation and propagation and are thus vulnerable to contamination with mycoplasmas. Some analyses have reported successful antibiotic clearance of contaminating mycoplasmas in Rickettsia cultures; however, many of these studies do not identify the contaminating mycoplasma species and often include only a few isolates. To our knowledge, there are no published studies reporting decontamination of mycoplasmas from Ehrlichia cultures. In this study, we developed a specific multiplex assay to identify two of the most common mycoplasma culture contaminants, Mycoplasma arginini and Mycoplasma orale , in cell cultures infected with Rickettsia or Ehrlichia species. We further describe the successful in vitro decontamination of M. arginini , M. orale, and co-contaminations with both mycoplasmas from multiple Rickettsia and Ehrlichia cultures using daptomycin and clindamycin. IMPORTANCE Mycoplasma contamination is a frequent problem in bacterial cell culture. These prolific organisms thrive in the extracellular environment in vitro and can persist in cell lines indefinitely without treatment. Historically, mycoplasma-contaminated Rickettsia cultures were cleared of contaminants by inoculating laboratory mice and re-isolating mycoplasma-free Rickettsia from brain endothelial cells. However, this method requires the sacrifice of live animals and is not always effective. Mycoplasma clearance via mouse inoculation requires a patent infection of murine central nervous system endothelial cells, which may not occur with some mildly pathogenic or nonpathogenic rickettsial species. In vitro antibiotic treatment represents an alternate method to eliminate contaminating mycoplasmas from rickettsial cultures. This method requires minimal adjustment of laboratories that already maintain rickettsial cultures and is not dependent on the use of laboratory animals. As such, the comprehensive strategy for Mycoplasma arginini and Mycoplasma orale elimination presented here can improve laboratory efficiency for in vitro research with intracellular bacteria.

Tickborne infections are challenging to diagnose, particularly among solid organ transplant recipients. We report a US case of donor-derived ehrlichiosis from a living kidney donation that highlights how screening for living donors may miss tickborne infections. Clinicians should consider the epidemiology of the donor when screening donations and evaluating recipients for donor-derived infection.

In the United States, the Amblyomma maculatum sensu lato (s.l.) group is represented by two, distinct allopatric clusters of hard ticks identified as morphotype II in the eastern US and morphotype III in the southwestern states. Previous studies have shown that the two entities have evolved very recently from a common ancestor, are morphologically distinguishable in the adult stage, and are reproductively incompatible. Because of the recent divergence of the two morphotypes, gene sequences usually analyzed for a phylogenetic species definition are insufficiently informative to assign them to separate species. Microsatellite loci are predominantly non-coding sequences, selectively neutral, and usually have higher mutation rates than mitochondrial and coding nuclear gene sequences. An estimate of their divergence time based on the analysis of 8 previously developed microsatellite loci confirmed the recent speciation hypothesis, dating the radiation to approx. 230-460 years ago. A strong bottleneck signature suggests the establishment of these populations after a 1000-fold reduction in the population size of origin.

Murine typhus, a fleaborne disease caused by the bacterium Rickettsia typhi, is found throughout temperate and tropical regions of the world. Transmission of R. typhi to humans involves several species of fleas, and most infections result from direct inoculation of R. typhi-infected flea feces into abrasions in the skin. We describe the transmission of R. typhi from an organ donor in Texas, USA, to 2 kidney transplant recipients. The donor and 1 recipient died from the infection. The occurrence of R. typhi transmission via transplantation is a harbinger for the reemergence of murine typhus in some of the most densely populated metropolitan areas of the United States. Our findings reinforce the need to improve healthcare provider and public awareness of this life-threatening but treatable infection.

Whipple's disease is rarely diagnosed in Latin America. We describe 2 patients with Tropheryma whipplei infection diagnosed in Mexico during 2019-2021. Diagnoses were confirmed by histopathology, electron microscopy, immunohistochemistry, and DNA amplification and sequencing analysis of the 16S rRNA gene. Clinicians should be aware of T. whipplei infection and associated syndromes.

A Rocky Mountain spotted fever (RMSF) epidemic has spread through the state of Baja California, Mexico over the last decade and a half, beginning in Mexicali, and subsequently to Tijuana and to Ensenada by 2018. In October of 2022, we surveyed dogs and homes in randomly selected Áreas Geoestadisticas Básicas (AGEBs) with and without reported human cases. Brown dog ticks ( Rhipicephalus sanguineus sensu lato) were found on 33.9% of dogs and in the yards of 23.6% of homes. Homes from AGEBs with cases had over a 6-fold increased odds of ticks being present in the yard than AGEBs without reported cases. Both dogs that were permitted to roam and the presence of roaming dogs in the neighborhood were strongly associated with tick infestation of dogs and homes. No ticks or blood samples were polymerase chain reaction-positive for Rickettsia (R.) rickettsii , the causative agent of RMSF, although 54.6% of dogs were seropositive for spotted fever group rickettsiae, and 17.4% were seropositive for typhus group rickettsiae. R. massiliae and R. felis were detected in eight (1.3%) and 29 (4.8%) ticks, respectively; and R. felis was also detected in eight (4.6%) dog blood samples. Although the pathogenic potential of these other rickettsial species and their role in RMSF transmission remains unclear, our data on tick burdens in dogs and homes as risk factors for RMSF exposure provide further support to the pivotal need to reduce tick burdens and the numbers of roaming dogs to successfully manage the RMSF epidemic in northern Mexico.

Leishmaniasis is an important travel-related parasitic infection in the United States. Treatment regimens vary by Leishmania species and require an accurate diagnosis. The sensitivity and specificity of diagnostic methods depend on the type and condition of specimen analyzed. To identify the best algorithm for detection of parasites in fresh and fixed tissue samples, we evaluated parasite cultures, two PCR methods, and Leishmania immunohistochemistry (IHC) in samples received by the CDC from 2012 through 2019. The sensitivity and specificity of IHC assays were evaluated in fresh specimens tested. Diagnostic accuracy for formalin-fixed tissue was evaluated by using PCR-based methods and IHC. Of 100 suspected cases with fresh tissue available, Leishmania spp. infection was identified by PCR in 56% (56/100) of specimens; from these, 80% (45/56) were positive by parasite culture and 59% (33/56) by IHC. Of 420 possible cases where only fixed specimens were available, 58% (244/420) were positive by IHC and/or PCR. Of these, 96% (235/420) were positive by IHC and 84% (204/420) by PCR-based methods. Overall parasite detection using all methodologies was similar for fresh and formalin-fixed tissue specimens (56% versus 58%, respectively). Although PCR-based methods were superior for diagnosis of leishmaniasis and species identification in fresh samples, IHC in combination with PCR increased the accuracy for Leishmania spp. detection in fixed samples. In conclusion, PCR is the most effective method for detecting Leishmania infection in fresh tissue samples, whereas for formalin-fixed samples, IHC and PCR-based methods should be used in combination.

Rocky Mountain spotted fever (RMSF) is a tickborne disease endemic in areas of the Americas. Persistent high incidence of the disease exists in northern Mexico, perpetuated by local populations of brown dog ticks (Rhipicephalus sanguineus sensu lato) and free-roaming dogs. Six cases of RMSF caused by Rickettsia rickettsii, including three deaths, were reported to the California Department of Public Health during July 2023-January 2024. All six patients were eventually determined to have had exposure to R. rickettsii in Tecate, Mexico, a municipality on the U.S. border that had not been previously described as a high-risk RMSF area. Identification and reporting of the cases were complicated by challenges in diagnosis. The serious nature of the disease and delays in initiating appropriate treatment can result in life-threatening consequences. Epidemiologic collaborations among local, state, federal, and international public health agencies were essential to identifying Tecate as the location of exposure. Further collaborations will be important for directing future prevention measures. Increased health care provider awareness of RMSF is critical on both sides of the border to facilitate earlier diagnosis and initiation of appropriate treatment.

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.

We document a case of Rickettsia parkeri rickettsiosis in a patient in Connecticut, USA, who became ill after a bite from a Gulf Coast tick (Amblyomma maculatum). We used PCR to amplify R. parkeri DNA from the detached tick. The patient showed a 4-fold rise in IgG reactive with R. parkeri antigens.

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.

Rocky Mountain spotted fever (RMSF) is an ongoing public health crisis in Mexico, particularly in states bordering the United States. The national highest incidence and mortality of RMSF occur in this region, resulting in a case-fatality rate that ranges annually between 10% and 50%, primarily affecting vulnerable groups such as children, elderly adults, and persons living in poverty. Multiple biological, environmental, and social determinants can explain its growing presence throughout the country and how it challenges the health system and society. It is necessary to integrate resources and capacities from health authorities, research centers, and society to succeed in dealing with this problem. Through a scientific symposium, a group of academicians, U.S. health officials, and Mexican health authorities met on November 8-10, 2023, in Hermosillo, Mexico, to discuss the current situation of RMSF across the country and the challenges associated with its occurrence. An urgent call for action to improve national capacity against RMSF in the aspects of epidemiological and acarological surveillance, diagnosis, medical care, case and outbreak prevention, health promotion, and research was urged by the experts. The One Health approach is a proven multidisciplinary strategy to integrate policies and interventions to mitigate and prevent the burden of cases, deaths, and suffering caused by RMSF in Mexico.