Inferring the Potential Distribution of an Emerging Rickettsiosis in America: The Case of Rickettsia parkeri

Identification and Characterization of Ectoparasite-Borne Pathogens Through Vector and Animal Surveillance in Andean Countries, South America

Infectious diseases transmitted by ectoparasites such as fleas, lice, mites, and ticks constitute a global public health problem. Tick-borne diseases are the most widely studied emerging ectoparasite-borne diseases (EBD) mainly due to their increasing incidence worldwide, including in South America. Furthermore, in Peru and neighboring Andean countries (Bolivia, Colombia, and Ecuador), surveillance reports indicate that Rickettsia species appear to be the most diverse and widely distributed ectoparasite-borne pathogens (EBP) followed by Babesia species, and with fewer species of Anaplasma, Bartonella, Borrelia, Ehrlichia, Coxiella, and Phlebovirus pathogens. Amblyomma, Dermacentor, Rhipicephalus, and Ixodes ticks were reported as the most predominant ectoparasites found infected with a diversity of EBP belonging to Rickettsia, Babesia, Anaplasma, Bartonella, and Ehrlichia species. Overall, people living in rural areas where agriculture and livestock production are their main economic means are at higher risk of EBD.

Spatial modeling and risk assessment of chagas disease vector distribution in Espírito Santo, Brazil: A comprehensive approach for targeted control

Chagas disease, a persistent and life-threatening infection caused by the protozoan Trypanosoma cruzi, remains a significant public health concern in Latin America. Despite the Brazilian State of Espírito Santo (ES) not being classified as a high-risk area, the presence of epidemiologically significant triatomines like Panstrongylus megistus suggests a latent risk of T. cruzi transmission. This study, employing spatial modeling, assesses the distribution of key triatomine species in ES and predicts areas at risk for Chagas disease transmission. Our models, constructed with Maxent, KUENM, and QGIS, identified high suitability for most species in ES's southeast and south regions, with P. diasi showing high suitability in the central-west. Notably, 13 autochthonous cases of vector-borne Chagas disease were reported between 2001 and 2023. The risk assessment highlighted significant risk areas corresponding to the locations of these cases, indicating that most regions in ES are at higher risk of P. megistus presence. These findings provide crucial insights for enhancing regional epidemiological surveillance and inform targeted vector control strategies, effectively addressing latent risks.

SFG and TG seropositivity in Humans suspected of TBD in Yucatan, Mexico

Since 1996, the incidence of rickettsiosis has been increasing in Yucatán, Mexico, but recent prevalence data are lacking. This study aimed to determine exposure to the Spotted Fever Group (SFG) and Typhus Group (TG) in human serum samples suspected of tick-borne diseases (TBD) between 2015 and 2022. A total of 620 samples were analysed using indirect immunofluorescence assay (IFA) to detect IgG antibodies against SFG (Rickettsia rickettsii) and TG (Rickettsia typhi), considering a titer of ≥64 as positive. Results showed that 103 samples (17%) were positive for R. rickettsii and 145 (24%) for R. typhi, while 256 (41%) and 229 (37%) were negative, respectively. There was a cross-reaction in 244 samples (39%). Individuals with contact with vectors, such as ticks, showed significant exposure to fleas (p = 0.0010). The study suggests a high prevalence of rickettsiosis and recommends prospective studies to assess the disease burden and strengthen surveillance and prevention in Yucatán, considering factors like temperature and ecological changes.

Molecular detection of rickettsial agents in Amblyomma maculatum ticks (Ixodida: Ixodidae) from Ecuador

Rickettsiales are obligate intracellular bacteria that need vertebrates and arthropods to maintain their life cycles. Some species of the genera Anaplasma, Ehrlichia, and Rickettsia are transmitted by ticks to both animals and humans and can cause mild to severe and even fatal cases. In the Americas, there is substantial data on rickettsial agents, encompassing both clinical cases and the detection of these agents in ticks, but in Ecuador, the information about them remains poorly understood. Therefore, the objective of this study was to detect molecularly rickettsial agents in Amblyomma maculatum ticks in both parasitic and free-living phases collected from domestic animals and pasture in five localities across three coastal provinces of Ecuador. Rickettsia parkeri, Candidatus Rickettsia andeanae, and Ehrlichia sp. were recorded in A. maculatum for the first time in Ecuador. These records were made in a region where antibodies to the Spotted Fever Rickettsia Group were detected in humans. Additional studies are needed to characterize Ehrlichia sp. at a specific level. Furthermore, recognizing the specific Rickettsiales species circulating in the ticks and the hosts within a region is crucial for assessing potential contact risks.

New records of Rhipicephalus linnaei infected by Rickettsia massiliae from Central Mexico

BACKGROUND

On the American continent, Rhipicephalus sanguineus s.l. comprises two species: Rhipicephalus linnaei and R. sanguineus s.s. Each species has been identified as a potential vector of at least one of five species of pathogenic bacteria of the genus Rickettsia. In particular, Rickettsia massiliae is one of three species with the greatest importance in public health at the continental level. In Mexico, this species is reported exclusively in the Nearctic states of Baja California and Chihuahua.

AIM

For this reason, the aim of this work was to provide new records of R. massiliae for the centre of the country derived from active acarological surveillance.

MATERIALS AND METHODS

During the period of February-October 2019, 29 dogs from six municipalities in the state of Morelos were sampled. Hosts were visually inspected, and ticks were recovered and identified morphologically and molecularly by amplification of the 16S rDNA gene. Subsequently, five genes from members of the genus Rickettsia were amplified and sequenced.

RESULTS

A total of 229 (117♀, 98♂ and 14 N) ticks identified as R. linnaei were recovered, two of which were positive for R. massiliae strains related to those recovered from Argentina and the United States.

CONCLUSIONS

This work provides the second record of R. massiliae infecting R. linnaei in Mexico and the Americas, increasing the geographic distribution of this Rickettsia species in the Neotropical region, and providing information on the possible role of R. linnaei as a potential vector of this microorganism.

Worldwide comparison between the potential distribution of Rhipicephalus microplus (Acari: Ixodidae) under climate change scenarios

The cattle tick Rhipicephalus microplus (Acari: Ixodidae) has demonstrated its ability to increase its distribution raising spatially its importance as a vector for zoonotic hemotropic pathogens. In this study, a global ecological niche model of R. microplus was built in different scenarios using Representative Concentration Pathway (RCP), Socio-Economic Pathway (SSP), and a climatic dataset to determine where the species could establish itself and thus affect the variability in the presentation of the hemotropic diseases they transmit. America, Africa and Oceania showed a higher probability for the presence of R. microplus in contrast to some countries in Europe and Asia in the ecological niche for the current period (1970-2000), but with the climate change, there was an increase in the ratio between the geographic range preserved between the RCP and SSP scenarios obtaining the greatest gain in the interplay of RCP4.5-SSP245. Our results allow to determine future changes in the distribution of the cattle tick according to the increase in environmental temperature and socio-economic development influenced by human development activities and trends; this work explores the possibility of designing integral maps between the vector and specific diseases.

Comparison of Climate Change Scenarios of Rhipicephalus sanguineus sensu lato (Latreille 1806) from México and the Boarders with Central America and the United States

In America, the presence of Rhipicephalus sanguineus sensu stricto and Rhipicephalus linnaei has been confirmed. Both species are found in sympatry in the southern United States, northern Mexico, southern Brazil, and Argentina. The objective of this work is to evaluate the projection of the potential distribution of the ecological niche of Rhipicephalus sanguineus sensu lato in two climate change scenarios in Mexico and the border with Central America and the United States. Initially, a database of personal collections of the authors, GBIF, Institute of Epidemiological Diagnosis and Reference, and scientific articles was built. The ENMs were projected for the current period and two future scenarios: RCP and SSP used for the kuenm R package, the ecological niche of R. sanguineus s.l. It is distributed throughout the Mexico and Texas (United States), along with the border areas between Central America, Mexico, and the United States. Finally, it is observed that the ecological niche of R. sanguineus s.l. in the current period coincides in three degrees with the routes of human migration. Based on this information, and mainly on the flow of migrants from Central America to the United States, the risk of a greater gene flow in this area increases, so the risk relating to this border is a latent point that must be analyzed.

‘Candidatus Rickettsia andeanae’ and Probable Exclusion of Rickettsia parkeri in Ticks from Dogs in a Natural Area of the Pampa Biome in Brazil

Spotted fever illness caused by the tick-borne pathogen Rickettsia parkeri has emerged in the Pampa biome in southern Brazil, where the tick Amblyomma tigrinum is implicated as the main vector. Because domestic dogs are commonly parasitized by A. tigrinum, this canid is also a suitable sentinel for R. parkeri-associated spotted fever. Herein, we investigate rickettsial infection in ticks, domestic dogs and small mammals in a natural reserve of the Pampa biome in southern Brazil. The ticks A. tigrinum, Amblyomma aureolatum and Rhipicephalus sanguineus were collected from dogs. Molecular analyses of ticks did not detect R. parkeri; however, at least 34% (21/61) of the A. tigrinum ticks were infected by the non-pathogenic agent ‘Candidatus Rickettsia andeanae’. Serological analyses revealed that only 14% and 3% of 36 dogs and 34 small mammals, respectively, were exposed to rickettsial antigens. These results indicate that the study area is not endemic for R. parkeri rickettsiosis. We tabulated 10 studies that reported rickettsial infection in A. tigrinum populations from South America. There was a strong negative correlation between the infection rates by R. parkeri and ‘Candidatus R. andeanae’ in A. tigrinum populations. We propose that high infection rates by ‘Candidatus R. andeanae’ might promote the exclusion of R. parkeri from A. tigrinum populations. The mechanisms for such exclusion are yet to be elucidated.

Substantial viral and bacterial diversity at the bat-tick interface

Ticks harbour a high diversity of viruses, bacteria and protozoa. The soft tick Carios vespertilionis (Argasidae) is a common ectoparasite of bats in the Palearctic region and is suspected to be vector and reservoir of viruses and other microbial species in bat populations, some of which may act as zoonotic agents for human disease. The Soprano pipistrelle (Pipistrellus pygmaeus, Vespertilionidae) is widely distributed in Europe, where it can be found inside or close to human habitation. We used meta-transcriptomic sequencing to determine the RNA virome and common microbiota in blood-fed C. vespertilionis ticks collected from a Soprano pipistrelle bat roosting site in south-central Sweden. Our analyses identified 16 viruses from 11 virus families, of which 15 viruses were novel. For the first time in Sweden we identified Issuk-Kul virus, a zoonotic arthropod-borne virus previously associated with outbreaks of acute febrile illness in humans. Probable bat-associated and tick-borne viruses were classified within the families Nairoviridae, Caliciviridae and Hepeviridae, while other invertebrate-associated viruses included members of the Dicistroviridae, Iflaviridae, Nodaviridae, Partitiviridae, Permutotetraviridae, Polycipiviridae and Solemoviridae. Similarly, we found abundant bacteria in C. vespertilionis, including genera with known tick-borne bacteria, such as Coxiella spp. and Rickettsia spp. These findings demonstrate the remarkable diversity of RNA viruses and bacteria present in C. vespertilionis and highlight the importance of bat-associated ectoparasite surveillance as an effective and non-invasive means to track viruses and bacteria circulating in bats and ticks.

Estimating the distribution of Oryzomys palustris, a potential key host in expanding rickettsial tick-borne disease risk

Increasingly, geographic approaches to assessing the risk of tick-borne diseases are being used to inform public health decision-making and surveillance efforts. The distributions of key tick species of medical importance are often modeled as a function of environmental factors, using niche modeling approaches to capture habitat suitability. However, this is often disconnected from the potential distribution of key host species, which may play an important role in the actual transmission cycle and risk potential in expanding tick-borne disease risk. Using species distribution modeling, we explore the potential geographic range of Oryzomys palustris, the marsh rice rat, which has been implicated as a potential reservoir host of Rickettsia parkeri, a pathogen transmitted by the Gulf Coast tick (Amblyomma maculatum) in the southeastern United States. Due to recent taxonomic reclassification of O. palustris subspecies, we reclassified geolocated collections records into the newer clade definitions. We modeled the distribution of the two updated clades in the region, establishing for the first time, range maps and distributions of these two clades. The predicted distribution of both clades indicates a largely Gulf and southeastern coastal distribution. Estimated suitable habitat for O. palustris extends into the southern portion of the Mid-Atlantic region, with a discontinuous, limited area of suitability in coastal California. Broader distribution predictions suggest potential incursions along the Mississippi River. We found considerable overlap of predicted O. palustris ranges with the distribution of A. maculatum, indicating the potential need for extended surveillance efforts in those overlapping areas and attention to the role of hosts in transmission cycles.

Brown Dog Tick (Rhipicephalus sanguineus Sensu Lato) Infection with Endosymbiont and Human Pathogenic Rickettsia spp., in Northeastern México

Of the documented tick-borne diseases infecting humans in México, Rocky Mountain spotted fever (RMSF), caused by the Gram-negative bacterium Rickettsia rickettsii, is responsible for most fatalities. Given recent evidence of brown dog tick, Rhipicephalus sanguineus s.l., as an emerging vector of human RMSF, we aimed to evaluate dogs and their ticks for rickettsiae infections as an initial step in assessing the establishment of this pathosystem in a poorly studied region of northeastern México while evaluating the use of dogs as sentinels for transmission/human disease risk. We sampled owned dogs living in six disadvantaged neighborhoods of Reynosa, northeastern México to collect whole blood and ticks. Of 168 dogs assessed, tick infestation prevalence was 53%, composed of exclusively Rh. sanguineus s. l. (n = 2170 ticks). Using PCR and sequencing, we identified an overall rickettsiae infection prevalence of 4.1% (n = 12/292) in ticks, in which eight dogs harbored at least one infected tick. Rickettsiae infections included Rickettsia amblyommatis and Rickettsia parkeri, both of which are emerging human pathogens, as well as Candidatus Rickettsia andeanae. This is the first documentation of pathogenic Rickettsia species in Rh. sanguineus s.l. collected from dogs from northeastern México. Domestic dog infestation with Rickettsia-infected ticks indicates ongoing transmission; thus, humans are at risk for exposure, and this underscores the importance of public and veterinary health surveillance for these pathogens.

Molecular confirmation of Rickettsia parkeri in humans from Southern Mexico

Human tick-borne rickettsioses are caused by Rickettsia africae, Rickettsia massiliae, Rickettsia parkeri, Rickettsia philipi and Rickettsia rickettsii in the American continent. Rickettsia parkeri represents the second most important agent of eschar-associated spotted fever throughout the American continent. In Mexico, the presence of three strains of this bacterium (Black Gap, Maculatum and Atlantic Rainforest) has recently been reported in four species of ticks from five states (Baja California, Campeche, Sonora, Tabasco and Veracruz) and rickettsaemia was demonstrated in a dog from the state of Yucatán. We report two human cases of R. parkeri-rickettsiosis from Yucatan, Mexico. These findings have increased the interest in R. parkeri surveillance in the human population, due to the fluctuating regional Spotted Fever morbidity and mortality in the country.

Potential distribution of Amblyomma mixtum (Koch, 1844) in climate change scenarios in the Americas

Amblyomma mixtum is a Neotropical generalist tick of medical and veterinary importance which is widely distributed from United States of America to Ecuador. The aim of this study was to evaluate changes in the geographic projections of the ecological niche models of A. mixtum in climate change scenarios in America. We constructed a database of published scientific publications, personal collections, personal communications, and online databases. Ecological niche modelling was performed with 15 Bioclimatic variables using kuenm in R and was projected to three time periods (Last Glacial Maximum, Current and 2050) for America. Our model indicated a wide distribution for A. mixtum, with higher probability of occurrence along the Gulf of Mexico and occurring in a lesser proportion in the Pacific states, Central America, and the northern part of South America. The areas of new invasion are located mainly on the border of Mexico with Guatemala and Belize, some regions of Central America and Colombia. We conclude that the ecological niche modelling are effective tools to infer the potential distribution of A. mixtum in America, in addition to helping to propose future measures of epidemiological control and surveillance in the new potential areas of invasion.