Opossums and Cat Fleas: New Insights in the Ecology of Murine Typhus in Galveston, Texas

Pathogenic rickettsiae utilize the phosphatidylserine binding receptor CD300f on macrophages for host invasion and pathogenesis

Some arthropod-borne obligate intracellular rickettsiae are among the most virulent human pathogens. Upon entry, Rickettsia species modulate immune (e.g., macrophages; MΦ) and non-immune cell (e.g., endothelial cells) responses to create a habitable environment for host colonization. In particular, MΦ play a crucial role in either terminating an infection at an early stage or succumbing to bacterial replication and colonization. However, our understanding on how Rickettsia species modulate crucial cellular processes within MΦ, including phagocytosis, and host cell defenses, to establish an intracytosolic replication niche, remain poorly defined. In this study, we describe a previously unappreciated mechanism, in which pathogenic rickettsiae infection is mediated by the phosphatidylserine (PS)-binding receptor, CD300f. We found that CD300f -/- mice but not wild-type (WT) C57BL/6J mice were protected against R. typhi - or R. rickettsii [ Shelia Smith ]-induced fatal rickettsiosis. Adoptative transfer studies further revealed that CD300f-expressing bone marrow-derived macrophages (BMDMΦ) are important mediators to control rickettsiosis in WT mice. Mechanistical analysis, using WT or CD300f -/- BMDMΦ, showed that CD300f facilitates the engulfment of both pathogenic R. typhi and R. rickettsii species, likely via a PS-mediated mechanism. Furthermore, CD300f was involved in the intracytosolic replication of both pathogenic rickettsiae by differentially modulating the anti-inflammatory Interleukin (IL)-10 and anti-rickettsial IL-1α and IL-1β cytokine responses. Collectively, our findings describe a previously unappreciated role for the efferocytic receptor, CD300f, to facilitate engulfment and the intracellular survival of pathogenic rickettsiae within the host.

Significance Statement

Vector-borne diseases, which are transmitted by hematophagous arthropods, like ticks and fleas, present a perilous threat to public health. In fact, tick- and flea-borne rickettsial diseases are on the rise globally and our current inadequate understanding on how Rickettsia interacts with their mammalian host has significantly impaired the development of effective interventions against pathogenic rickettsial infections. Here, we identified the phosphatidylserine (PS)-receptor, CD300f, as an important mediator of pathogenic rickettsiae infection in vivo and in vitro . Specifically, we showed that CD300f-expressing macrophages facilitate rickettsial infection by differentially modulating anti-inflammatory Interleukin (IL)-10 and anti-rickettsial IL-1α and IL-1β cytokine responses. In sum, our data described CD300f as an important regulator of rickettsial infection and may present a target for therapeutic intervention.

Cat Flea Coinfection with Rickettsia felis and Rickettsia typhi

Purpose: Flea-borne rickettsioses, collectively referred to as a term for etiological agents Rickettsia felis, Rickettsia typhi, and RFLOs (R. felis-like organisms), has become a public health concern around the world, specifically in the United States. Due to a shared arthropod vector (the cat flea) and clinical signs, discriminating between Rickettsia species has proven difficult. While the effects of microbial coinfections in the vector can result in antagonistic or synergistic interrelationships, subsequently altering potential human exposure and disease, the impact of bacterial interactions within flea populations remains poorly defined. Methods: In this study, in vitro and in vivo systems were utilized to assess rickettsial interactions in arthropods. Results: Coinfection of both R. felis and R. typhi within a tick-derived cell line indicated that the two species could infect the same cell, but distinct growth kinetics led to reduced R. felis growth over time, regardless of infection order. Sequential flea coinfections revealed the vector could acquire both Rickettsia spp. and sustain coinfection for up to 2 weeks, but rickettsial loads in coinfected fleas and feces were altered during coinfection. Conclusion: Altered rickettsial loads during coinfection suggest R. felis and R. typhi interactions may enhance the transmission potential of either agent. Thus, this study provides a functional foundation to disentangle transmission events propelled by complex interspecies relationships during vector coinfections.

Autophagy facilitates intracellular survival of pathogenic rickettsiae in macrophages via evasion of autophagosomal maturation and reduction of microbicidal pro-inflammatory IL-1 cytokine responses

IMPORTANCE

Rickettsia spp. are intracellular bacterial parasites of a wide range of arthropod and vertebrate hosts. Some rickettsiae are responsible for several severe human diseases globally. One interesting feature of these pathogens is their ability to exploit host cytosolic defense responses to their benefits. However, the precise mechanism by which pathogenic Rickettsia spp. elude host defense responses remains unclear. Here, we observed that pathogenic Rickettsia typhi and Rickettsia rickettsii (Sheila Smith [SS]), but not non-pathogenic Rickettsia montanensis, become ubiquitinated and induce autophagy upon entry into macrophages. Moreover, unlike R. montanensis, R. typhi and R. rickettsii (SS) colocalized with LC3B but not with Lamp2 upon host cell entry. Finally, we observed that both R. typhi and R. rickettsii (SS), but not R. montanensis, reduce pro-inflammatory interleukin-1 (IL-1) responses, likely via an autophagy-mediated mechanism. In summary, we identified a previously unappreciated pathway by which both pathogenic R. typhi and R. rickettsii (SS) become ubiquitinated, induce autophagy, avoid autolysosomal destruction, and reduce microbicidal IL-1 cytokine responses to establish an intracytosolic niche in macrophages.

Murine Typhus: A Review of a Reemerging Flea-Borne Rickettsiosis with Potential for Neurologic Manifestations and Sequalae

Murine typhus is an acute febrile illness caused by Rickettsia typhi, an obligately intracellular Gram-negative coccobacillus. Rats (Rattus species) and their fleas (Xenopsylla cheopis) serve as the reservoir and vector of R. typhi, respectively. Humans become infected when R. typhi-infected flea feces are rubbed into flea bite wounds or onto mucous membranes. The disease is endemic throughout much of the world, especially in tropical and subtropical seaboard regions where rats are common. Murine typhus is reemerging as an important cause of febrile illness in Texas and Southern California, where an alternate transmission cycle likely involves opossums (Didelphis virginiana) and cat fleas (Ctenocephalides felis). Although primarily an undifferentiated febrile illness, a range of neurologic manifestations may occur, especially when treatment is delayed. Serology is the mainstay of diagnostic testing, but confirmation usually requires demonstrating seroconversion or a fourfold increase in antibody titer from acute- and convalescent-phase sera (antibodies are seldom detectable in the first week of illness). Thus, early empiric treatment with doxycycline, the drug of choice, is imperative. The purpose of this review is to highlight murine typhus as an important emerging and reemerging infectious disease, review its neurologic manifestations, and discuss areas in need of further study.

Vector-Borne Disease in Wild Mammals Impacted by Urban Expansion and Climate Change

Ecologies of zoonotic vector-borne diseases may shift with climate and land use change. As many urban-adapted mammals can host ectoparasites and pathogens of human and animal health concern, our goal was to compare patterns of arthropod-borne disease among medium-sized mammals across gradients of rural to urban landscapes in multiple regions of California. DNA of Anaplasma phagocytophilum was found in 1-5% of raccoons, coyotes, and San Joaquin kit foxes; Borrelia burgdorferi in one coyote, rickettsiae in two desert kit foxes, and Yersinia pestis in two coyotes. There was serological evidence of rickettsiae in 14-37% of coyotes, Virginia opossums, and foxes; and A. phagocytophilum in 6-40% of coyotes, raccoons, Virginia opossums, and foxes. Of six flea species, one Ctenocephalides felis from a raccoon was positive for Y. pestis, and Ct. felis and Pulex simulans fleas tested positive for Rickettsia felis and R. senegalensis. A Dermacentor similis tick off a San Joaquin kit fox was PCR-positive for A. phagocytophilum. There were three statistically significant risk factors: risk of A. phagocytophilum PCR-positivity was threefold greater in fall vs the other three seasons; hosts adjacent to urban areas had sevenfold increased A. phagocytophilum seropositivity compared with urban and rural areas; and there was a significant spatial cluster of rickettsiae within greater Los Angeles. Animals in areas where urban and rural habitats interconnect can serve as sentinels during times of change in disease risk.

Confirmation of the presence of Rickettsia felis infecting Ornithodoros puertoricensis in Mexico

Soft ticks are neglected competent vectors of a wide range of pathogenic microorganisms, among which bacteria of the genera Rickettsia and Borrelia stand out. In Mexico, previous studies have shown the presence of a member of the Ornithodoros talaje complex in the Virginia opossum (Didelphis virginiana Didelphimorphia: Didelphidae Kerr) from southeastern Mexico. However, its specific identification has not been achieved. Two D. virginiana were treated in a private clinic during the period of April-May 2022. Tick larvae were manually removed, DNA extraction was performed, and some genes from various bacterial and parasitic pathogens were amplified and sequenced. A total of 96 larvae were recovered, which were morphologically identified as Ornithodoros puertoricensis (Ixodida: Argasidae Fox); the 16 S sequences showed a similarity of 96.79%-99.51% with sequences of O. puertoricensis from Panama and Colombia. The presence of Rickettsia felis (Rickettsiales: Rickettsiaceae Bouyer et al.) was detected in 15 specimens from one host. The soft tick O. puertoricensis is recorded for the first time as an ectoparasite of the Virginia opossum in America and represents the second report for this soft tick in Mexico since 1963. This represents the most northern record of this tick species in its geographic distribution and brings a new soft tick-Rickettsia association.

Increased Seroprevalence of Typhus Group Rickettsiosis, Galveston County, Texas, USA

Whether increases in typhus group rickettsiosis in Galveston County, Texas, USA, are caused by increased recognition or true reemergence is unclear. We conducted a serosurvey that demonstrated Rickettsia typhi antibodies increased from 1.2% in 2013 to 7.8% in 2021 (p<0.001). These findings support pathogen reemergence rather than enhanced recognition alone.

Molecular Detection of Rickettsia felis in Fleas of Companion Animals in East Texas

Flea-borne spotted fever is an emerging insect-borne rickettsial infection caused by Rickettsia felis and has been identified worldwide. This study sought to explore the prevalence of rickettsiae associated with fleas on companion dogs and cats from Walker and Montgomery Counties in East Texas. Fleas were collected from animals entering local veterinary clinics for routine checkups. Collected fleas were identified as Ctenocephalides felis or Pulex irritans and analyzed by polymerase chain reaction for the presence of rickettsiae and subsequent sequencing. An estimation of the bcMLE (bias-corrected maximum likelihood estimation) of pooled samples was calculated. Four hundred eighty-eight fleas (comprising C. felis and P. irritans) were collected from 16 cats and 77 dogs. Our results demonstrate R. felis in 21 pools of fleas from dogs (bcMLE 15.28%) and a bcMLE of 7.25% from flea samples collected from cats. Sequence analysis revealed R. felis as the only Rickettsia that could be amplified in our samples using the rickettsial citrate synthase gene and subsequent sequencing. In this study, the presence of R. felis in fleas from companion cats and dogs suggests a potential risk of flea-borne spotted fever in humans who encounter flea-infested animals.

Socio-ecological determinants of rickettsial seroprevalence in a rural community of Yucatán, Mexico

Rickettsial diseases have seen a re-emergence in the Americas in the last few decades, with concerning morbidity, mortality and economic implications that result from loss of productivity, income, curbs in liberal trade agreements, and reduction in agricultural practices. The aim of this study is to determine the socioecological determinants and seroprevalence for Rickettsia typhi and Rickettsia rickettsii among residents of Teabo, a rural community of Yucatán, Mexico. Sociodemographic data and serum samples were obtained from 180 consenting participants. Antibody titers for R. typhi and R. rickettsii were determined by indirect immunofluorescence assay (IFA). Participants also submitted tick samples collected from their residential area. We conducted logistic regression models to evaluate the association between exposure variables and seroprevalence. Rhipicephalus sanguineus s.l. (37%; n = 65), and Amblyomma cajennense Fabricius (17%; n = 29) were the predominant tick species in peri-domestic areas. Out of the 180 participants, there was significantly higher seroprevalence of R. typhi (n = 77; 46%) compared to R. rickettsii [n = 27, 15%, (p < 0.05)]. Pearson's chi-square test of independence revealed significant differences in R. rickettsii seroprevalence by gender (X² [n = 175, df = 4, (p < 0.001)] = 180.26), level of education, (X² [n = 180, df = 4, (p < 0.001)] = 44.0), and by tick species found in residential area, (X² [n = 180, df = 4, (p = 0.050)] = 9.48). After adjusting for other variables in a logistic regression model, for each unit increase in the number of dogs present in the residential area, there was a 27% increase in the odds of human seroprevalence for R. typhi IgG (AOR = 1.27, 95% CI: 1.01-1.63). Compared to study participants living in residential areas with a 'low' height of vegetation, those living in residential areas with a 'medium' height of vegetation had 2.5 times greater odds of human seroprevalence for R. typhi IgG (AOR = 2.51, 95% CI: 1.19-5.40). Potentially modifiable existing factors in the peri-domestic area may constitute a high-risk source of seroprevalence for rickettsial antibodies among residents of the rural community of Teabo, Yucatán, Mexico.

Experimental Rickettsia typhi Infection in Monodelphis domestica: Implications for Opossums as an Amplifying Host in the Suburban Cycle of Murine Typhus

Murine typhus is an acute undifferentiated febrile illness caused by Rickettsia typhi. In the United States, its reemergence appears to be driven by a shift from the classic rat-rat flea cycle of transmission to one involving opossums (Didelphis virginiana) and cat fleas. Little is known of the ability of opossums to act as a reservoir and amplifying host for R. typhi. Here, we use Monodelphis domestica (the laboratory opossum) as a surrogate for D. virginiana. Opossums were inoculated via the intraperitoneal (IP) or intradermal (ID) route with 1 × 106 viable R. typhi. Blood and tissues were collected on days 6, 13, 20, and 27 or if moribund. Although one ID-infected opossum died, the remainder did not appear ill, whereas half of the IP-inoculated animals succumbed to infection. Rickettsemia was demonstrated in all animals through week 2 of infection and sporadically in weeks 3 and 4. Rickettsia typhi DNA was detected in all tissues, with most animals demonstrating the presence of bacteria into weeks 3 and 4. Histopathology and immunohistochemistry demonstrated typical findings of rickettsial infection. Akin to infection in rats, the demonstration of disseminated infection, typical inflammation, and prolonged rickettsemia with relatively few clinical effects (especially in the more natural route of ID inoculation) supports the potential of opossums to act as a competent mammalian reservoir and component of the zoonotic maintenance cycle of R. typhi. Understanding the dynamics of infection within opossums may have implications for the prevention and control of murine typhus.

Genetic typing of isolates of Rickettsia typhi

Murine typhus, which is caused by Rickettsia typhi, has a wide range of clinical manifestations. It has a low mortality rate but may result in meningoencephalitis and interstitial pneumonia in severe cases. Comparisons of complete genome sequences of R. typhi isolates from North Carolina, USA (Wilmington), Myanmar (B9991PP), and Thailand (TH1527) identified only 26 single nucleotide polymorphism (SNP) and 7 insertion-deletion (INDEL) sites in these highly syntenic genomes. Assays were developed to further define the distribution of these variant sites among 15 additional isolates of R. typhi with different histories from Asia, the USA, and Africa. Mismatch amplification mutation assays (MAMA) were validated for 22 SNP sites, while the 7 INDEL sites were analyzed directly on agarose gels. Six SNP types, 9 INDEL types, 11 total types were identified among these 18 isolates. Replicate DNA samples as well as comparisons of isolates with different passage and source histories gave consistent genetic typing profiles. Comparison of the SNP and INDEL markers to R. typhi’s nearest neighbor Rickettsia prowazekii demonstrated that the majority of the SNPs represent intra-species variation that arose post divergence of these two species while several INDEL sites also exhibited intraspecies variability among the R. prowazekii genomes that have been completely sequenced. The assays for the presence of these SNP and INDEL sites, particularly the latter, comprise a low technology gel method for consistently distinguishing R. typhi and R. prowazekii as well as for differentiating genetic types of R. typhi.

Rickettsia typhi is an obligately intracellular bacterium which is most commonly transmitted by rat fleas to humans and can cause the disease murine (endemic) typhus wherever both humans and infected rats are present. However, this agent is also present in a variety of other arthropod species associated with other vertebrate animals. Its closest relative is Rickettsia prowazekii, the etiologic agent of epidemic typhus (human louse-borne) and sylvatic typhus (associated with flying squirrels and its ectoparasites in the Eastern United States). Both classic louse-borne and flea-borne typhus rickettsiae can cause fatal infections and have the potential for use as biothreat agents as they can be grown in large quantities. We investigated the genetic differences that can be found in different stocks of R. typhi. Our work is important for two reasons. We have developed robust and sensitive methods for distinguishing isolates of R. typhi originating from different continents; these new assays require only simple instrumentation which is available in nearly all biology laboratories. Our results also provided new insights confirming the probable origin of R. typhi in Asia and its likely cosmopolitan spread by rats on ships around the world.

All for One Health and One Health for All: Considerations for Successful Citizen Science Projects Conducting Vector Surveillance from Animal Hosts

Simple Summary

Vector-borne diseases are often zoonotic and so a One Health approach must be employed in order to investigate and control them. Therefore, surveillance of arthropod vectors and pathogens among animal populations should complement human disease surveillance. Since traditional surveillance methods to collect arthropod vectors and conduct pathogen testing from animals can be challenging, data collection can be supplemented with citizen science approaches, where the general public is actively involved in collecting animals and/or samples. In this review, we discuss considerations for researchers to create a successful vector surveillance program using citizen science approaches with different stakeholders who own, have interests in, or work with animals.

Abstract

Many vector-borne diseases that affect humans are zoonotic, often involving some animal host amplifying the pathogen and infecting an arthropod vector, followed by pathogen spillover into the human population via the bite of the infected vector. As urbanization, globalization, travel, and trade continue to increase, so does the risk posed by vector-borne diseases and spillover events. With the introduction of new vectors and potential pathogens as well as range expansions of native vectors, it is vital to conduct vector and vector-borne disease surveillance. Traditional surveillance methods can be time-consuming and labor-intensive, especially when surveillance involves sampling from animals. In order to monitor for potential vector-borne disease threats, researchers have turned to the public to help with data collection. To address vector-borne disease and animal conservation needs, we conducted a literature review of studies from the United States and Canada utilizing citizen science efforts to collect arthropods of public health and veterinary interest from animals. We identified common stakeholder groups, the types of surveillance that are common with each group, and the literature gaps on understudied vectors and populations. From this review, we synthesized considerations for future research projects involving citizen scientist collection of arthropods that affect humans and animals.

Rise in Murine Typhus in Galveston County, Texas, USA, 2018

Murine typhus, an undifferentiated febrile illness caused by Rickettsia typhi, is increasing in prevalence and distribution throughout Texas. In 2018, a total of 40 cases of murine typhus were reported in Galveston County. This increase, unprecedented since the 1940s, highlights the importance of awareness by physicians and public health officials.

Rickettsia-host interaction: strategies of intracytosolic host colonization

Bacterial infection is a highly complex biological process involving a dynamic interaction between the invading microorganism and the host. Specifically, intracellular pathogens seize control over the host cellular processes including membrane dynamics, actin cytoskeleton, phosphoinositide metabolism, intracellular trafficking and immune defense mechanisms to promote their host colonization. To accomplish such challenging tasks, virulent bacteria deploy unique species-specific secreted effectors to evade and/or subvert cellular defense surveillance mechanisms to establish a replication niche. However, despite superficially similar infection strategies, diverse Rickettsia species utilize different effector repertoires to promote host colonization. This review will discuss our current understandings on how different Rickettsia species deploy their effector arsenal to manipulate host cellular processes to promote their intracytosolic life within the mammalian host.

Urban ecology of hosts and vectors of Rickettsia in a rickettsiosis-endemic city of the Yucatan peninsula, Mexico

Rickettsioses are vector-borne zoonotic diseases that occur in urban environments. Currently, they are associated with the presence of domestic and synanthropic animals, the ectoparasites that they harbor, and their local habitat. The implementation of prevention actions relies on the understanding of the local ecology of interactions between hosts, vector species, and the etiologic agents. In this context, this study aimed to explore and describe the occurrence of infected mammals and their ectoparasites in human urban dwellings, and those characteristics of urban dwellings associated to the presence of Rickettsia infected animals in groups of households where at least one human case of rickettsiosis has occurred in the previous year of the study. Briefly, blood-samples and ectoparasites from synanthropic and domestic animals, were obtained from groups of households from different areas of an urban settlement. Serologic and molecular diagnostics helped to identify Spotted Fever Group (SFG) and TG (Typhus Group) Rickettsia in animal and ectoparasite samples. A total of 99 mammals were sampled, 29 opossums (Didelphis virginiana), 13 house mice (Mus musculus), seven black rats (Rattus rattus) and 50 dogs. Infection occurrence in opossums was 8.3% of SFG, 50% for TG, and 4.2% of undetermined group. For house mice 46.2% for SFG and 30.8% were undetermined. Black rats 28.6% of SFG and 57.1% undetermined. Finally, dogs were 19.1% of SFG, 57.4% to TG, and 23.4% belonged to undetermined group. A total of 424 ectoparasites were collected from the mammals. In opossums occurred the ticks Ambyomma sp., Ornithodoros (Alecterobius) nr. talaje, and the flea Ctenocephalides felis. In dogs we found the ticks Rhipicephalus sanguineus s. l., Amblyomma sp., O. (A.) nr. talaje, and the flea Ct. felis. No ectoparasites were collected from rodents. The occurrence of infected animals was associated primarily with the material of the backyard floor, the type of sanitary system in the household, the presence of garbage in the backyard, presence of firewood storage, stored polyethylene terephthalate (PET) containers for sale to recyclers, and the store of construction supplies in the backyard. Nonetheless a generalized linear model showed that the household with a backyard with a dirt floor or other non-concrete material has more chances of harboring infected animals (RR= 1.74, 95% CI= 1.07-2.84 and RR= 1.03, 95% CI= 0.39-2.32 respectively). In contrast, when the house has a sanitary system of urban sewer system or a latrine outside de house, the chances of having infected animals decreased significantly (RR= 0.39, 95% CI= 0.12-0.94 and RR= 0.46, 95% CI= 0.03-2.22). We conclude that both SFG and TG rickettsioses occur in animals and their ectoparasites in peridomiciles of urban households were at least one human rickettsiosis case had occurred.

Murine Typhus Infection in Pregnancy: Case Series and Literature Review

Murine typhus is a flea-borne disease of worldwide distribution with a recent reemergence in the United States of America. There are limited data about the presentation, treatment, and outcomes in the pregnant population. We report on two cases of murine typhus during pregnancy and review the literature to compile previously reported cases. A comprehensive search was performed via the PubMed database for published articles between 1990 and 2020. Seven articles met the criteria of symptomatic pregnant murine typhus infection. A total of 37 patients were identified. Patients frequently presented with a prolonged duration of fevers prior to presentation, headache, and elevated hepatic transaminases. The diagnosis was predominantly based on serology. Treatment varied. Overall, the pregnancy outcome was favorable. Murine typhus can mimic other pregnancy-related pathologies. More exclusive and large-scale studies are needed to learn more of murine typhus during pregnancy.

Amplicon-Based Next Generation Sequencing for Rapid Identification of Rickettsia and Ectoparasite Species from Entomological Surveillance in Thailand

BACKGROUND

Next generation sequencing (NGS) technology has been used for a wide range of epidemiological and surveillance studies. Here, we used amplicon-based NGS to species identify Rickettsia and their arthropod hosts from entomological surveillance.

METHODS

During 2015-2016, we screened 1825 samples of rodents and ectoparasites collected from rodents and domestic mammals (dog, cat, and cattle) across Thailand for Rickettsia. The citrate synthase gene was amplified to identify Rickettsia to species, while the Cytochrome Oxidase subunit I (COI) and subunit II (COII) genes were used as target genes for ectoparasite identification. All target gene amplicons were pooled for library preparation and sequenced with Illumina MiSeq platform.

RESULT

The highest percentage of Rickettsia DNA was observed in fleas collected from domestic animals (56%) predominantly dogs. Only a few samples of ticks from domestic animals, rodent fleas, and rodent tissue were positive for Rickettisia DNA. NGS based characterization of Rickettsia by host identified Rickettsia asembonensis as the most common bacteria in positive fleas collected from dogs (83.2%) while "Candidatus Rickettsia senegalensis" was detected in only 16.8% of Rickettsia positive dog fleas. Sequence analysis of COI and COII revealed that almost all fleas collected from dogs were Ctenocephalides felis orientis. Other Rickettsia species were detected by NGS including Rickettsia heilongjiangensis from two Haemaphysalis hystricis ticks, and Rickettsia typhi in two rodent tissue samples.

CONCLUSION

This study demonstrates the utility of NGS for high-throughput sequencing in the species characterization/identification of bacteria and ectoparasite for entomological surveillance of rickettsiae. A high percentage of C. f. orientis are positive for R. asembonensis. In addition, our findings indicate there is a risk of tick-borne Spotted Fever Group rickettsiosis, and flea-borne murine typhus transmission in Tak and Phangnga provinces of Thailand.

Parasites of Native and Invasive Rodents in Chile: Ecological and Human Health Needs

Invasive populations are a threat to biodiversity, resulting in the loss of species, and also a threat to human health, participating in the reservoir of diseases. Rodents are among the most important invasive species worldwide. Chile is a country that features island conditions in terms of geography and has been widely invaded by allochthonous rodents. In this mini-review, we updated the literature on macro-parasites infecting both native and invasive rodents and of vector-borne pathogens in continental Chile in order to assess the relative importance of invasive rodents from both ecological and public health points of view. A total of 174 parasite species were found, with Siphonaptera representing the most diverse group. When examining how parasites are shared between native and introduced rodents, the analysis suggests that parasites circulate freely within recipient populations, and are not significantly transmitted from source populations. Further, generalist parasites are typically more prone to being shared between native and introduced rodents. Most zoonotic parasites were reported in invasive rodents, suggesting that these rodents must represent a public health concern. Although several vector-borne pathogens have been reported in rodents or ectoparasites, most of the recently emerging research has illustrated that there is a lack of evidence on rodent-vector-borne zoonoses in most pathogens.

Manifestations and Management of Flea-Borne Rickettsioses

Murine typhus and flea-borne spotted fever are undifferentiated febrile illnesses caused by Rickettsia typhi and Rickettsia felis, respectively. These organisms are small obligately intracellular bacteria and are transmitted to humans by fleas. Murine typhus is endemic to coastal areas of the tropics and subtropics (especially port cities), where rats are the primary mammalian host and rat fleas (Xenopsylla cheopis) are the vector. In the United States, a cycle of transmission involving opossums and cat fleas (Ctenocephalides felis) are the presumed reservoir and vector, respectively. The incidence and distribution of murine typhus appear to be increasing in endemic areas of the US. Rickettsia felis has also been reported throughout the world and is found within the ubiquitous cat flea. Flea-borne rickettsioses manifest as an undifferentiated febrile illness. Headache, malaise, and myalgia are frequent symptoms that accompany fever. The incidence of rash is variable, so its absence should not dissuade the clinician to consider a rickettsial illness as part of the differential diagnosis. When present, the rash is usually macular or papular. Although not a feature of murine typhus, eschar has been found in 12% of those with flea-borne spotted fever. Confirmatory laboratory diagnosis is usually obtained by serology; the indirect immunofluorescence assay is the serologic test of choice. Antibodies are seldom present during the first few days of illness. Thus, the diagnosis requires acute- and convalescent-phase specimens to document seroconversion or a four-fold increase in antibody titer. Since laboratory diagnosis is usually retrospective, when a flea-borne rickettsiosis is considered, empiric treatment should be initiated. The treatment of choice for both children and adults is doxycycline, which results in a swift and effective response. The following review is aimed to summarize the key clinical, epidemiological, ecological, diagnostic, and treatment aspects of flea-borne rickettsioses.

History, Rats, Fleas, and Opossums. II. The Decline and Resurgence of Flea-Borne Typhus in the United States, 1945-2019

Flea-borne typhus, due to Rickettsia typhi and R. felis, is an infection causing fever, headache, rash, and diverse organ manifestations that can result in critical illness or death. This is the second part of a two-part series describing the rise, decline, and resurgence of flea-borne typhus (FBT) in the United States over the last century. These studies illustrate the influence of historical events, social conditions, technology, and public health interventions on the prevalence of a vector-borne disease. Flea-borne typhus was an emerging disease, primarily in the Southern USA and California, from 1910 to 1945. The primary reservoirs in this period were the rats Rattus norvegicus and Ra. rattus and the main vector was the Oriental rat flea (Xenopsylla cheopis). The period 1930 to 1945 saw a dramatic rise in the number of reported cases. This was due to conditions favorable to the proliferation of rodents and their fleas during the Depression and World War II years, including: dilapidated, overcrowded housing; poor environmental sanitation; and the difficulty of importing insecticides and rodenticides during wartime. About 42,000 cases were reported between 1931-1946, and the actual number of cases may have been three-fold higher. The number of annual cases of FBT peaked in 1944 at 5401 cases. American involvement in World War II, in the short term, further perpetuated the epidemic of FBT by the increased production of food crops in the American South and by promoting crowded and unsanitary conditions in the Southern cities. However, ultimately, World War II proved to be a powerful catalyst in the control of FBT by improving standards of living and providing the tools for typhus control, such as synthetic insecticides and novel rodenticides. A vigorous program for the control of FBT was conducted by the US Public Health Service from 1945 to 1952, using insecticides, rodenticides, and environmental sanitation and remediation. Government programs and relative economic prosperity in the South also resulted in slum clearance and improved housing, which reduced rodent harborage. By 1956, the number of cases of FBT in the United States had dropped dramatically to only 98. Federally funded projects for rat control continued until the mid-1980s. Effective antibiotics for FBT, such as the tetracyclines, came into clinical practice in the late 1940s. The first diagnostic test for FBT, the Weil-Felix test, was found to have inadequate sensitivity and specificity and was replaced by complement fixation in the 1940s and the indirect fluorescent antibody test in the 1980s. A second organism causing FBT, R. felis, was discovered in 1990. Flea-borne typhus persists in the United States, primarily in South and Central Texas, the Los Angeles area, and Hawaii. In the former two areas, the opossum (Didelphis virginiana) and cats have replaced rats as the primary reservoirs, with the cat flea (Ctenocephalides felis) now as the most important vector. In Hawaii, 73% of cases occur in Maui County because it has lower rainfall than other areas. Despite great successes against FBT in the post-World War II era, it has proved difficult to eliminate because it is now associated with our companion animals, stray pets, opossums, and the cat flea, an abundant and non-selective vector. In the new millennium, cases of FBT are increasing in Texas and California. In 2018-2019, Los Angeles County experienced a resurgence of FBT, with rats as the reservoir.

Urban foci of murine typhus involving cat fleas (Ctenocephalides felis felis) collected from opossums in Mexico City

Murine typhus, a neglected rickettsiosis caused by Rickettsia typhi, is a common disease in several Latin-American countries. The sylvatic life cycle of R. typhi encompasses the presence of several wild mammals, particularly opossums of the genus Didelphis and their associated fleas. Due to the colonization of wild environments by human populations, the increase in contact with opossum fleas has generated the presence of urban outbreaks of typhus. For this reason, the aim of our study was to identify the presence and diversity of Rickettsia sp. in fleas collected from opossums of an urban reserve in Mexico City. Opossums were captured from February to September 2017. For the detection of Rickettsia DNA, fragments of 800 bp of the citrate synthase (gltA) and the outer membrane protein B (ompB) were amplified. A total of 141 fleas (111 ♀, 30 ♂) of a single species (Ctenocephalides felis felis) were recovered from 31 Didelphis virginiana. Rickettsia DNA was detected in 17.7% (25/141) of the analysed fleas, recovered from seven infested opossums. The Maximum likelihood of sequences exhibited an identity of 99%-100% with sequences of R. typhi from southern United States. This work represents the first record of R. typhi in fleas from opossums in Mexico.

Detection of Rickettsia asembonensis in Fleas (Siphonaptera: Pulicidae, Ceratophyllidae) Collected in Five Counties in Georgia, United States

We conducted a molecular survey of Rickettsia in fleas collected from opossums, road-killed and live-trapped in peridomestic and rural settings, state parks, and from pet cats and dogs in Georgia, United States during 1992-2014. The cat flea, Ctenocephalides felis (Bouché) was the predominant species collected from cats and among the archival specimens from opossums found in peridomestic settings. Polygenis gwyni (Fox) was more prevalent on opossums and a single cotton rat trapped in sylvatic settings. Trapped animals were infested infrequently with the squirrel flea, Orchopeas howardi (Baker) and C. felis. TaqMan assays targeting the BioB gene of Rickettsia felis and the OmpB gene of Rickettsia typhi were used to test 291 flea DNAs for Rickettsia. A subset of 53 C. felis collected from a cat in 2011 was tested in 18 pools which were all bioB TaqMan positive (34% minimum infection prevalence). Of 238 fleas tested individually, 140 (58.8%, 95% confidence interval [CI]: 52.5-64.9%) DNAs were bioB positive. Detection of bioB was more prevalent in individual C. felis (91%) compared to P. gwyni (13.4%). Twenty-one (7.2%) were ompB TaqMan positive, including 18 C. felis (9.5%) and 3 P. gwyni (3.2%). Most of these fleas were also positive with bioB TaqMan; however, sequencing of gltA amplicons detected only DNA of Rickettsia asembonensis. Furthermore, only the R. asembonensis genotype was identified based on NlaIV restriction analysis of a larger ompB fragment. These findings contribute to understanding the diversity of Rickettsia associated with fleas in Georgia and emphasize the need for development of more specific molecular tools for detection and field research on rickettsial pathogens.

Low occurrence of Bartonella in synanthropic mammals and associated ectoparasites in peri-urban areas from Central-Western and Southern Brazil

Worldwide, Bartonella species are known to infect a wide range of mammalian and arthropod hosts, including humans. The current study aimed to investigate the prevalence of Bartonella spp. in synanthropic mammals captured in peri-urban areas from Central-Western and Southern Brazil and their ectoparasites. For this aim, 160 mammals belonging to four species, and 218 associated arthropods were sampled. DNA was extracted and subjected to different Bartonella screening assays. Additionally, blood samples from 48 small rodents were submitted to liquid BAPGM culture followed by qPCR assay and solid culture. Two out of 55 Rattus captured in Santa Catarina state were PCR-positive for Bartonella when targeting the nuoG, 16S, and ITS loci. Sequences showed high homology with Bartonella coopersplainsensis. Conversely, all 48 small rodents, 14 capybaras and 43 opossum DNA samples from animals trapped in Mato Grosso do Sul were Bartonella negative in the HRM real time PCR assays targeting the ITS locus and gltA gene. Additionally, all mammal-associated ectoparasites showed negativity results based on HRM real time PCR assays. The present study showed, for the first time, the occurrence of B. coopersplainsensis in Brazil, shedding some light on the distribution of rats-related Bartonella in South America. In addition, the majority of rodents and marsupials were negative for Bartonella spp. Since B. coopersplainsensis reservoirs - Rattus spp. - are widely dispersed around the globe, their zoonotic potential should be further investigated.

A chromosome-level assembly of the cat flea genome uncovers rampant gene duplication and genome size plasticity

BACKGROUND

Fleas (Insecta: Siphonaptera) are small flightless parasites of birds and mammals; their blood-feeding can transmit many serious pathogens (i.e., the etiological agents of bubonic plague, endemic and murine typhus). The lack of flea genome assemblies has hindered research, especially comparisons to other disease vectors. Accordingly, we sequenced the genome of the cat flea, Ctenocephalides felis, an insect with substantial human health and veterinary importance across the globe.

RESULTS

By combining Illumina and PacBio sequencing of DNA derived from multiple inbred female fleas with Hi-C scaffolding techniques, we generated a chromosome-level genome assembly for C. felis. Unexpectedly, our assembly revealed extensive gene duplication across the entire genome, exemplified by ~ 38% of protein-coding genes with two or more copies and over 4000 tRNA genes. A broad range of genome size determinations (433-551 Mb) for individual fleas sampled across different populations supports the widespread presence of fluctuating copy number variation (CNV) in C. felis. Similarly, broad genome sizes were also calculated for individuals of Xenopsylla cheopis (Oriental rat flea), indicating that this remarkable "genome-in-flux" phenomenon could be a siphonapteran-wide trait. Finally, from the C. felis sequence reads, we also generated closed genomes for two novel strains of Wolbachia, one parasitic and one symbiotic, found to co-infect individual fleas.

CONCLUSION

Rampant CNV in C. felis has dire implications for gene-targeting pest control measures and stands to complicate standard normalization procedures utilized in comparative transcriptomics analysis. Coupled with co-infection by novel Wolbachia endosymbionts-potential tools for blocking pathogen transmission-these oddities highlight a unique and underappreciated disease vector.

Risk1, a Phosphatidylinositol 3-Kinase Effector, Promotes Rickettsia typhi Intracellular Survival

Rickettsia species are Gram-negative obligate intracellular bacteria that infect a wide range of eukaryotes and vertebrates. In particular, human body louse-borne Rickettsia prowazekii and flea-borne Rickettsia typhi have historically plagued humankind and continue to reemerge globally. The unavailability of vaccines and limited effectiveness of antibiotics late in infection place lethality rates up to 30%, highlighting the need to elucidate the mechanisms of Rickettsia pathogenicity in greater detail. Here, we characterize a new effector, Risk1, as a secreted phosphatidylinositol 3-kinase (PI3K) with unique dual class I and class III activities. Risk1 is required for host colonization, and its vacuolar phosphatidylinositol 3-phosphate generation modulates endosomal trafficking to arrest autophagosomal maturation. Collectively, Risk1 facilitates R. typhi growth by altering phosphoinositide metabolism and subverting intracellular trafficking.

To establish a habitable intracellular niche, various pathogenic bacteria secrete effectors that target intracellular trafficking and modulate phosphoinositide (PI) metabolism. Murine typhus, caused by the obligate intracellular bacterium Rickettsia typhi, remains a severe disease in humans. However, the mechanisms by which R. typhi effector molecules contribute to internalization by induced phagocytosis and subsequent phagosomal escape into the cytosol to facilitate the intracellular growth of the bacteria remain ill-defined. Here, we characterize a new molecule, Risk1, as a phosphatidylinositol 3-kinase (PI3K) secreted effector and the first bacterial secretory kinase with both class I and III PI3K activities. Inactivation of Risk1 PI3K activities reduced the phosphorylation of phosphatidylinositol 4,5-bisphosphate to phosphatidylinositol 3,4,5-trisphosphate within the host, which consequently diminished host colonization by R. typhi. During infection, Risk1 targets the Rab5-EEA1-phosphatidylinositol 3-phosphate [PI(3)P] signaling axis to promote bacterial phagosomal escape. Subsequently, R. typhi undergoes ubiquitination and induces host autophagy; however, maturation to autolysosomes is subverted to support intracellular growth. Intriguingly, only enzymatically active Risk1 binds the Beclin-1 core complex and contributes to R. typhi-induced autophagosome formation. In sum, our data suggest that Risk1, with dual class I and class III PI3K activities, alters host PI metabolism and consequently subverts intracellular trafficking to facilitate intracellular growth of R. typhi.

Trypanosoma cruzi infections and associated pathology in urban-dwelling Virginia opossums (Didelphis virginiana)

Trypanosoma cruzi, a zoonotic protozoan parasite, infects a wide range of mammals. The southern United States has endemic sylvatic transmission cycles maintained by several species of wildlife and domestic dogs. We hypothesized that urban-dwelling opossums (Didelphis virginiana) in South Texas are infected with T. cruzi, and that tissue pathology would be associated with infection. In 2017, we collected blood, heart tissue and anal gland secretions from 100 wild opossums across three seasons that were trapped by animal control in South Texas. In addition, anal gland tissue and intercostal muscle were collected from 43 of the 100 opossums for which time allowed the extra tissue collection. All blood, tissue, and secretion samples were screened for T. cruzi DNA using qPCR with confirmation of positive status achieved through one or more additional PCR assays, including a qPCR to determine the parasite discrete typing unit (DTU). T. cruzi DNA was detected in at least one tissue of 15% of the opossums sampled: blood clot (9%), heart tissue (10%), anal gland secretions (12%), intercostal muscle (16.3%), and anal gland tissue (11.6%). Infection was detected in two or more different tissue types in nine of the opossums. The 35 tissues for which parasite DTU was determined were exclusively 'Tcl'- a DTU previously associated with locally-acquired human disease in the United States. T. cruzi-positive opossums were nearly 14 times more likely to exhibit significant heart lesions on histopathology (lympoplasmacytic inflammation±fibrosis) when compared to negative opossums (OR = 13.56, CI = 1.23-751.28, p-value = 0.03). Three triatomines were opportunistically collected from the study site, of which two were infected (66.7%), and bloodmeal analysis revealed canine, opossum, and human bloodmeals. Given the presence of parasite in opossum blood, unique potential for shedding of parasite in anal glad secretions, and evidence of vectors feeding on opossums, it is likely that opossums serve as wild reservoirs around urban dwellings in South Texas.

Candidatus Rickettsia senegalensis in Cat Fleas (Siphonaptera: Pulicidae) Collected from Dogs and Cats in Cauca, Colombia

Rickettsia typhi and Rickettsia felis (Rickettsiales: Rickettsiaceae) are flea-transmitted pathogens. They are important causes of acute febrile illness throughout the world. We, therefore, sought to identify the rickettsial species present in the fleas of dogs and cats in the department of Cauca, Colombia. In this study, we collected 1,242 fleas from 132 dogs and 43 fleas from 11 cats. All fleas were morphologically identified as Ctenocephalides felis (Bouché) adults and organized in pools for DNA extraction (234 pools from dogs and 11 from cats). The gltA gene from rickettsiae was targeted for screening amplification using conventional PCR. In total, 144 of the 245 pools (58.7%) were positive. The positive samples were then processed for the amplification of the 17kDa antigen gene (144/144; 100% positive) and sca5 gene (140/144; 97.2% positive). In addition, restriction enzyme length polymorphism analysis using NlaIV on the amplified product of the sca5 gene demonstrated several organisms: 21/140 (15%) were R. felis, 118/140 (84.3%) were Rickettsia asemboensis, and 1/140 (0.7%) were Candidatus Rickettsia senegalensis. Subsequent sequencing confirmed Candidatus Rickettsia senegalensis in C. felis collected from dogs the first reported from Colombia.

Fleas of Shrews and Rodents in Rural Lowland Taiwan

Fleas transmit a variety of pathogens to humans but are relatively understudied in comparison to mosquitoes and ticks, including in Taiwan, where fleas in rural lowlands have never been systematically surveyed. In total, 700 fleas of four species were collected from 1,260 shrews and rodents at nine counties across lowland Taiwan. Nosopsyllus nicanus Jordan (Siphonaptera: Ceratophyllidae) and Xenopsylla cheopis Rothschild (Siphonaptera: Pulicidae) were the most abundant flea species (79.0 and 14.6% of total fleas, respectively); the former was largely limited to the islets, while the latter was restricted to the Taiwan main island. Rattus losea Swinhoe (Rodentia: Muridae) was the most common small mammal species (49.3% of total) and hosted the majority of fleas (88.3% of total). Five Rickettsia spp., including Rickettsia conorii Brumpt (Rickettsiales: Rickettsiaceae), Rickettsia felis Bouyer et al. Rickettsia japonica Uchida, Rickettsia raoultii Mediannikov, and Rickettsia rickettsii Brumpt or closely related species, were identified from 67 individually assayed fleas based on ompB and gltA genes. Rickettsia felis, mainly transmitted by fleas, was detected in one X. cheopis in southern Taiwan where a confirmed human case of infection with R. felis has been reported. The presence of R. felis, along with the other four tick-borne Rickettsia spp., demonstrates that a variety of rickettsiae circulate in rural lowland Taiwan and could pose risks to human health.

High Morbidity Due to Murine Typhus Upsurge in Urban Neighborhoods in Central Israel

The incidence of murine typhus in Israel has decreased substantially since 1950 to a low of 0.04/100,000 population in 2010. We present the experience of a single university medical center in central Israel. Hospitalized patients serologically positive for Rickettsia typhi by indirect immunofluorescence antibody assay during 2006-2016 were retrospectively identified. Clinical and laboratory data from patients' charts were used to analyze disease trends and distribution. Seventy-eight patients were studied (mean age: 27.9 years), mostly of Arab ethnicity (68, 87.2%). Seventy-one (91%) patients resided in two large mixed Jewish-Arab cities-Lod and Ramla. The incidence of murine typhus among the Arab population in Lod increased 8.4-fold from 6.4/100,000 in 2006 to a peak of 53.4/100,000 in 2013. The average annual incidence among Arabs in Ramla was 10.1/100,000. Among Jews, incidences were 0.8/100,000 in Lod and 0.4/100,000 in Ramla. The classical triad of fever, headache, and rash was noted in 20.8% patients. Substantial morbidity included prolonged fever before hospitalization and hospital stay (mean of 8.4 and 5.1 days, respectively), and severe complications in six patients, including pneumonitis in three patients, and splenic infarctions, pericardial effusion, and retinitis, each in one. One previously healthy patient died of multiorgan failure. The study describes a high incidence of murine typhus with a recent upsurge in an urban setting in central Israel. High morbidity and a single fatal outcome challenge the concept of murine typhus being a mild disease. The study calls for better rodent control and sanitation measures in the affected neighborhoods.

Climate factors driven typhus group rickettsiosis incidence dynamics in Xishuangbanna Dai autonomous prefecture of Yunnan province in China, 2005-2017

BACKGROUND

Typhus group rickettsiosis (TGR), which is a neglected vector-borne infectious disease, including epidemic typhus and endemic typhus. We explored the lag effects and nonlinear association between meteorological factors and TGR incidence in Xishuangbanna Dai autonomous prefecture from 2005 to 2017, China.

METHODS

A Poisson regression with a distributed lag nonlinear model (DLNM) was utilized to analyze TGR cases data and the contemporaneous meteorological data.

RESULTS

A J-shaped nonlinear association between weekly mean temperature and TGR incidence was found. The cumulative exposure to weekly mean temperature indicated that the RR increased with the increment of temperature. Taking the median value as the reference, lower temperatures could decrease the risk of TGR incidence, while higher temperatures could increase the risk of TGR incidence and last for 21 weeks. We also found a reversed U-shaped nonlinear association between weekly mean precipitation and TGR incidence. Precipitation between 5 mm and 13 mm could increase the risk of TGR incidence. Taking the median value as the reference, no precipitation and lower precipitation could decrease the risk of TGR incidence, while higher precipitation could increase the risk of TGR incidence and last for 18 weeks.

CONCLUSIONS

The prevention and control measures of TGR should be implemented according to climatic conditions by the local government and health departments in order to improve the efficiency.

Epidemiological characteristics and spatiotemporal patterns of typhus group rickettsiosis at the county level in China, 2005-2017

OBJECTIVE

To explore the epidemiological characteristics and spatiotemporal patterns of typhus group rickettsiosis (TGR) in mainland China.

METHODS

A chi-squared test was used to compare the differences in the age and occupation distributions across the different years. Time-series analyses, spatial clustering analyses, and spatiotemporal scan statistics were used to detect the spatiotemporal patterns of the TGR incidence.

RESULTS

A total of 29,211 TGR cases were collected. Of these cases, 63.1% occurred from May to October, and 88.4% occurred in individuals between 0 and 59 years old. There was a significant spatial TGR heterogeneity from 2005 to 2017. The hotspots were located mainly in the southwestern, southern, and circum-Bohai Sea regions of northern China. Eighteen spatiotemporal clusters were observed using Kulldorff's space-time scan statistic, and the primary cluster included three counties, Jinghong city, Menghai county, and Mengla county.

CONCLUSIONS

TGR is widely distributed in China, and it is a serious threat to public health. The hotspots were located mainly in the southwestern, southern, and circum-Bohai Sea regions of northern China, and the primary spatiotemporal cluster showed a trend shifting from circum-Bohai Sea regions to the southwestern regions. Targeted interventions should be executed in high-risk regions for precise prevention and control.

The Rickettsioses: A Practical Update

Rickettsia are small, obligately intracellular, gram-negative bacilli. They are distributed among a variety of hematophagous arthropod vectors and cause illness throughout the world. Rickettsioses present as an acute undifferentiated febrile illness and are often accompanied by headache, myalgias, and malaise. Cutaneous manifestations include rash and eschar, which both occur at varying incidence depending on the infecting species. Serology is the mainstay of diagnosis, and the indirect immunofluorescence assay is the test of choice. Reactive antibodies are seldom present during early illness, so testing should be performed on both acute-phase and convalescent-phase sera. Doxycycline is the treatment of choice.

Differentiation of Rickettsia felis and Rickettsia felis-Like Organisms via Restriction Fragment Length Polymorphism Analysis

Rickettsia typhi and Rickettsia felis are flea-borne pathogens, which cause murine typhus and flea-borne spotted fever, respectively. Recently, two other flea-borne rickettsiae (phylogenetically similar to R. felis) have been discovered-Rickettsia asembonensis and Candidatus Rickettsia senegalensis. Currently, species-specific identification of detected organisms requires sequencing- or probe-based PCR assays. Our aim was to develop an efficient and inexpensive method to differentiate R. felis and R. felis-like organisms through restriction fragment length polymorphism (RFLP) analysis. Outer membrane protein B sequences of the aforementioned flea-borne rickettsiae were analyzed using DNASTAR Lasergene Core software to focus on the region amplified by the primers 120.2788 and 120.3599. Restriction enzyme digestion sites were identified, and in silico digestions of each species were compared through simulated agarose gels. The enzyme NlaIV was determined to be the most effective at creating a unique banding pattern within the area of interest. To confirm the predicted performance of NlaIV digestion, we tested the DNA of known PCR positive Ctenocephalides felis fleas collected from cats and opossums within Galveston, Texas. DNA from these fleas was amplified using the sca5 primer set 120.2788 and 120.3599. The PCR products were then digested with NlaIV, subjected to polyacrylamide gel electrophoresis, and visualized through ethidium bromide staining. The banding patterns were then compared with the computer-generated digestion patterns. All samples demonstrated a banding pattern consistent with the predicted pattern for the known species, as confirmed by previous sequencing. This RFLP assay was developed to be an efficient and cost-effective method to screen samples for R. felis, R. asembonensis, and Candidatus R. senegalensis. We believe this assay can aid in the epidemiological and ecological studies of flea-borne rickettsiae.

Rickettsiae Within the Fleas of Feral Cats in Galveston, Texas

Murine typhus is a flea-borne typhus group rickettsiosis caused by Rickettsia typhi. Once a prevalent disease in the United States, the use of dichlorodiphenyltrichloroethane in the 1940s broke the classic rat-rat flea cycle of transmission, and the remaining endemic foci are now believed to be associated with opossums and the cat flea (Ctenocephalides felis). In Galveston, Texas murine typhus has re-emerged as a cause of febrile illness, and 7% of fleas collected from opossums are infected with R. typhi. In this study, we sought to explore the prevalence of rickettsiae associated with fleas on cats, as these animals have been speculated to play a role in the epidemiology of murine typhus. Fleas were collected from feral cats entering a local veterinary clinic as part of a trap, spay, neuter, and release program. Fleas were identified and subjected to analysis by PCR and sequencing. An estimation of the minimum infection rate (MIR) of pooled samples was performed. Three hundred fourteen fleas (all C. felis) were collected from 24 cats. Sequences for the outer membrane protein B gene revealed R. typhi in one pool (MIR 0.3%), Rickettsia felis in four pools (MIR 1.3%), Rickettsia asembonensis in one pool (MIR 0.3%), and "Candidatus R. senegalensis" in six pools (MIR 2.0%). Results were confirmed by sequencing portions of the rickettsial citrate synthase and 17-kD protein gene. In this study, the presence of R. typhi in fleas from cats suggests that in Galveston, there exists a small but measurable risk to humans who come into contact with flea-infested cats. Despite this, we believe that the low prevalence from cat-collected fleas, compared with that previously detected from opossums, makes cats less likely to play a role in the maintenance of R. typhi in this region. The significance of other identified flea-borne rickettsiae is yet to be elucidated.

Identification of Rickettsial Infections (Rickettsia sp. TH2014) in Ctenocephalides orientis Fleas (Siphonaptera: Pulicidae)

Rickettsia felis (Rickettsiales: Rickettsiaceae) is an emergent human pathogen that causes febrile illnesses in various parts of the world. This study describes the identification and growth characteristics of a R. felis-like organism (designated as Rickettsia sp. TH2014) cultured from Ctenocephalides orientis fleas in rural Malaysia. In this study, culturing of rickettsiae from filtered triturated flea lysates was performed in Aedes albopictus C6/36 cells. Cytopathic effects were observed from one of the samples 4 d post-inoculation. Electron microscopy revealed actively replicating intracytosolic coccobacillary organisms in the rickettsia-infected cells. Sequence analysis of amplified citrate synthase (gltA) gene fragment shows complete match of the rickettsia with Rickettsia sp. Rf31 in Southeast Asia, and 'Candidatus Rickettsia senegalensis' strain PU01-02 in Africa. The whole-genome sequence of Rickettsia sp. TH2014 was determined and assembled. The estimated genome size and guanine + cytosine content of the rickettsia are 1.37 Mb and 32.9%, respectively. The high values of average nucleotide identity and tetra-nucleotide signature correlation index obtained from pairwise genome comparison study suggest the identification of the rickettsia as R. felis. The whole-genome single-nucleotide polymorphism analysis demonstrates close genetic relatedness of the rickettsia with R. felis and Rickettsia asemboensis. However, based on sequence analyses of rickettsial genes (16S rDNA, gltA, ompB, and sca4), Rickettsia sp. TH2014 is found to be distinct from R. felis and R. asemboensis. The sequence analyses reveal that Rickettsia sp. TH2014 is highly similar to 'Ca. Rickettsia senegalensis' detected in fleas from Africa, Asia, and North America. Further investigation to provide insights on pathogenic potential and transmission dynamics of the rickettsia is warranted.

Molecular Detection of Vector-Borne Pathogens in Rural Dogs and Associated Ctenocephalides felis Fleas (Siphonaptera: Pulicidae) in Easter Island (Chile)

The presence of vector-borne pathogens of veterinary and public health interest have received little attention in Chile. In Easter Island, in particular, a Chilean territory in the southeastern Pacific Ocean, no information is available. To fill this gap, 153 rural dogs were inspected for ectoparasites during a sterilization campaign carried out in 2016. Fleas were observed in 46% of the dogs, and Ctenocephalides felis (Bouché, 1835) was the only species present. Morphological identification of fleas was genetically confirmed using conventional polymerase chain reaction targeting the cox2 gene. No tick was observed in any dog. The presence of DNA of Rickettsia sp. (gltA and ompA fragment genes), Anaplasmataceae (16S rRNA), and Bartonella sp. (16S-23S ribosomal RNA intergenic spacer) was investigated in blood samples of 70 of the dogs and in 126 fleas analyzed in 68 pools that included 1-5 fleas. Rickettsial DNA was detected in 97% (n = 66) of the flea pools. Of these, 57 showed between 99 and 100% identity for both genes with published sequences of Candidatus Rickettsia asemboensis (CRa), six with Rickettsia felis, and one with Candidatus Rickettsia senegalensis. For two pools, gltA amplicons were identical to CRa but ompB amplicions showed 99-100% identity with R. felis. Anaplasmataceae DNA was detected in 16% (n = 11) pools. Sequenced amplicons showed highest identity with the endosymbiont Wolbachia pipientis. Bartonella DNA, showing 99% identity to Bartonella clarridgeiae, was detected in one pool (1.4%). No positive reaction was observed for any dog. This is the first detection of members of the 'R. felis-like' group other than R. felis in Chile.

Acute Febrile Illness and Complications Due to Murine Typhus, Texas, USA1,2

Murine typhus occurs relatively commonly in southern Texas, as well as in California. We reviewed records of 90 adults and children in whom murine typhus was diagnosed during a 3-year period in 2 hospitals in southern Texas, USA. Most patients lacked notable comorbidities; all were immunocompetent. Initial signs and symptoms included fever (99%), malaise (82%), headache (77%), fatigue (70%), myalgias (68%), and rash (39%). Complications, often severe, in 28% of patients included bronchiolitis, pneumonia, meningitis, septic shock, cholecystitis, pancreatitis, myositis, and rhabdomyolysis; the last 3 are previously unreported in murine typhus. Low serum albumin and elevated procalcitonin, consistent with bacterial sepsis, were observed in >70% of cases. Rash was more common in children; thrombocytopenia, hyponatremia, elevated hepatic transaminases, and complications were more frequent in adults. Murine typhus should be considered as a diagnostic possibility in cases of acute febrile illness in southern and even in more northern US states.

Analysis of Health-Care Charges in Murine Typhus: Need for Improved Clinical Recognition and Diagnostics for Acute Disease

Murine typhus, caused by Rickettsia typhi, is an undifferentiated febrile illness with no available rapid and sensitive diagnostic assay for use during early disease. We aimed to compare the health-care charges in those diagnosed with murine typhus to those with influenza, a febrile illness with an available rapid diagnostic test. A comparison of health-care-associated charges at the University of Texas Medical Branch at Galveston demonstrated a median of $817 for influenza versus $16,760 for murine typhus (P < 0.0001). Median laboratory ($184 versus $3,254 [P < 0.0001]) and imaging charges ($0 versus $514 [P < 0.0001]) were also higher in those with murine typhus. Those receiving at least one imaging study during their illness were greater in the murine typhus group (91.3% versus 20.3%) (P < 0.0001). The median time needed to establish a confirmed or presumptive diagnosis was 2 days for influenza compared with 9 days for murine typhus (P < 0.0001). The median number of health-care encounters was greater for those with murine typhus (2 versus 1) (P < 0.0001). Eleven patients (15.9%) with influenza were hospitalized as a result of their illness compared with 16 (69.6%) with murine typhus (P < 0.0001). The estimated mortality based on disease severity at presentation by Acute Physiology and Chronic Health Evaluation II scoring was similar in the two groups-both had a median 4% mortality risk (P = 0.0893). These results highlight the need for improved clinical recognition and diagnostics for acute rickettsioses such as murine typhus.

The rise of neglected tropical diseases in the "new Texas"

Within the last five years, the State of Texas has experienced either transmission or outbreaks of Ebola, chikungunya, West Nile, and Zika virus infections. Autochthonous transmission of neglected parasitic and bacterial diseases has also become increasingly reported. The rise of such emerging and neglected tropical diseases (NTDs) has not occurred by accident but instead reflects rapidly evolving changes and shifts in a “new” Texas beset by modern and globalizing forces that include rapid expansions in population together with urbanization and human migrations, altered transportation patterns, climate change, steeply declining vaccination rates, and a new paradigm of poverty known as “blue marble health.” Summarized here are the major NTDs now affecting Texas. In addition to the vector-borne viral diseases highlighted above, there also is a high level of parasitic infections, including Chagas disease, trichomoniasis, and possibly leishmaniasis and toxocariasis, as well as typhus-group rickettsiosis, a vector-borne bacterial infection. I also highlight some of the key shifts in emerging and neglected disease patterns, partly due to an altered and evolving economic and ecological landscape in the new Texas, and provide some preliminary disease burden estimates for the major prevalent and incident NTDs.

Suspected and Confirmed Vector-Borne Rickettsioses of North America Associated with Human Diseases

The identification of pathogenic rickettsial agents has expanded over the last two decades. In North America, the majority of human cases are caused by tick-borne rickettsioses but rickettsiae transmitted by lice, fleas, mites and other arthropods are also responsible for clinical disease. Symptoms are generally nonspecific or mimic other infectious diseases; therefore, diagnosis and treatment may be delayed. While infection with most rickettsioses is relatively mild, delayed diagnosis and treatment may lead to increased morbidity and mortality. This review will discuss the ecology, epidemiology and public health importance of suspected and confirmed vector-transmitted Rickettsia species of North America associated with human diseases.

First Detection of Rickettsia typhi and Rickettsia felis in Fleas Collected From Client-Owned Companion Animals in the Southern Great Plains

Flea-borne rickettsiosis occurs worldwide and includes a number of pathogens, namely, Rickettsia typhi and Rickettsia felis. Most studies in the United States have occurred in southern Texas and California where flea-borne rickettsiosis is endemic, resulting in a lack of information from other regions of the country. Between March and August 2016, 222 fleas were collected from 52 client-owned dogs and cats in two urban areas in Oklahoma. Fleas were identified using morphological characteristics then pooled and tested by polymerase chain reaction (PCR) using published primers for gltA, ompB, and 17-kDa. The majority (98.6%) of fleas collected were Ctenocephalides felis (Bouché) followed by Pulex irritans (L) (1.4%). Overall, fleas collected from 30.0% (6/20) cats and 43.8% (14/32) dogs were infected with R. felis. Three C. felis-pools collected from three dogs, two in the Enid area (central Oklahoma) and one in the Elk City area (western Oklahoma), were infected with R. typhi as well as R. felis. 'Candidatus R. senegalensis' was detected in one pool of fleas taken from a cat in Oklahoma City. This is the first evidence that flea-borne Rickettsia species occur in fleas obtained from client-owned dogs and cats in the Great Plains region. The impact of these Rickettsia species on public health in the region needs further investigation.

Bacterial arthropod-borne diseases in West Africa

Arthropods such as ticks, lice, fleas and mites are excellent vectors for many pathogenic agents including bacteria, protozoa and viruses to animals. Moreover, many of these pathogens can also be accidentally transmitted to humans throughout the world. Bacterial vector-borne diseases seem to be numerous and very important in human pathology, however, they are often ignored and are not well known. Yet they are in a phase of geographic expansion and play an important role in the etiology of febrile episodes in regions of Africa. Since the introduction of molecular techniques, the presence of these pathogens has been confirmed in various samples from arthropods and animals, and more rarely from human samples in West Africa. In this review, the aim is to summarize the latest information about vector-borne bacteria, focusing on West Africa from 2000 until today in order to better understand the epidemiological risks associated with these arthropods. This will allow health and veterinary authorities to develop a strategy for surveillance of arthropods and bacterial disease in order to protect people and animals.

Direct evidence of Rickettsia typhi infection in Rhipicephalus sanguineus ticks and their canine hosts

Murine typhus is a rickettsiosis caused by Rickettsia typhi, whose transmission is carried out by rat fleas in urban settlements as classically known, but it also has been related to cat fleas in a sub-urban alternative cycle that has been suggested by recent reports. These studies remarks that in addition to rats, other animals like cats, opossums and dogs could be implied in the transmission of Rickettsia typhi as infected fleas obtained from serologically positive animals have been detected in samples from endemic areas. In Mexico, the higher number of murine typhus cases have been detected in the Yucatan peninsula, which includes a great southeastern region of Mexico that shows ecologic characteristics similar to the sub-urban alternative cycle recently described in Texas and California at the United States. To find out which are the particular ecologic characteristics of murine typhus transmission in this region, we analyzed blood and Rhipicephalus sanguineus ticks obtained from domestic dogs by molecular approaches, demonstrating that both samples were infected by Rickettsia typhi. Following this, we obtained isolates that were analyzed by genetic sequencing to corroborate this infection in 100% of the analyzed samples. This evidence suggests for the first time that ticks and dogs could be actively participating in the transmission of murine typhus, in a role that requires further studies for its precise description.

Significance of major international seaports in the distribution of murine typhus in Taiwan

Background

International seaports are hotspots for disease invasion and pathogens can persist in seaports even after ports are abandoned. Transmitted by fleas infected by Rickettsia typhi, murine typhus, a largely neglected and easily misdiagnosed disease, is known to occur primarily in large seaports. However, the significance of seaports in the occurrence of murine typhus has never been validated quantitatively.

Methodology/Principal findings

We studied the spatial distribution of murine typhus, a notifiable disease, in Taiwan. We investigated whether risk of infection was correlated with distance to international seaports and a collection of environmental and socioeconomic factors, using a Bayesian negative binomial conditionally autoregressive model, followed with geographically weighted regression. Seaports that are currently in use and those that operated in the 19^th century for trade with China, but were later abandoned due to siltation were analyzed. A total of 476 human cases of murine typhus were reported during 2000–2014 in the main island of Taiwan, with spatial clustering in districts in southwest and central-west Taiwan. A higher incidence rate (case/population) was associated with a smaller distance to currently in-use international seaports and lower rainfall and temperature, but was uncorrelated with distance to abandoned ports. Geographically weighted regression revealed a geographic heterogeneity in the importance of distance to in-use seaports near the four international seaports of Taiwan.

Conclusions/Significance

Our study suggests that murine typhus is associated with international seaports, especially for those with large trading volume. Thus, one of the costs of global trade in Taiwan might be elevated risks of murine typhus. Globalization has accelerated the spread of infectious diseases, but the burden of disease varies geographically, with regions surrounding major international seaports warranting particular surveillance.

Globalization has hastened the spread of infectious diseases, with seaports as hotspots for disease invasion. Transmitted by fleas infected with the rickettsia Rickettsia typhi, murine typhus occurs worldwide, but its significance as a common causative agent of illness in tropical regions remains largely neglected. Although it is recognized that murine typhus is prevalent primarily in large seaports, the significance of seaports in the occurrence of murine typhus has never been validated quantitatively. We thus investigated whether distribution of murine typhus in Taiwan was associated with international seaports. Notably, abandoned international seaports (abandoned in the 19^th century due to siltation) were also studied to see whether the causative agent of murine typhus might still circulate around the ports even after being abandoned. We found that infection risk of murine typhus was negatively associated with distance to operating seaports but was uncorrelated with nearness to abandoned seaports. In addition, the importance of distance to operating seaports for risk of murine typhus infection varied spatially. Our study highlights elevated disease risk as a cost of international trade and suggests particular surveillance in regions surrounding major international seaports.

Flea-Borne Rickettsioses and Rickettsiae

Rickettsia typhi and Rickettsia felis are flea-borne rickettsiae that are distributed throughout the world. This mini-review outlines the ecology and epidemiology of flea-borne rickettsioses; highlights important clinical, diagnostic, and therapeutic considerations; and discusses areas of uncertainty regarding Rickettsia felis and other rickettsiae harbored by fleas.