Challenges posed by tick-borne rickettsiae: eco-epidemiology and public health implications

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.

Ticks and tick-borne diseases from Mallorca Island, Spain

Ixodid ticks are obligate blood-feeding arthropods and important vectors of pathogens. In Mallorca, almost no data on the tick fauna are available. Herein, we investigated ticks and tick-borne pathogens in ticks collected from dogs, a cat and humans in Mallorca as result of a citizen science project. A total of 91 ticks were received from German tourists and residents in Mallorca. Ticks were collected from March to October 2023 from dogs, cat and humans, morphologically and genetically identified and tested for pathogens by PCRs. Six tick species could be identified: Ixodes ricinus (n = 2), Ixodes ventalloi (n = 1), Hyalomma lusitanicum (n = 7), Hyalomma marginatum (n = 1), Rhipicephalus sanguineus s.l. (n = 71) and Rhipicephalus pusillus (n = 9). Rhipicephalus sanguineus s.l. adults were collected from dogs and four females from a cat and the 16S rDNA sequences identified it as Rh. sanguineus s.s. Hyalomma lusitanicum was collected from 1 human, 1 dog and 5 specimens were collected from the ground in the community of Santanyi, together with one H. marginatum male. This is the first report of Hyalomma marginatum in Mallorca. Both I. ricinus were collected from humans and I. ventalloi female was collected from a dog. All ticks tested negative for Anaplasma phagocytophilum, Coxiella spp., Francisella spp., and piroplasms. In 32/71 (45%) specimens of Rh. sanguineus s.s., Rickettsia spp. could be detected and in 18/32 (56.2%) sequenced tick DNAs R. massiliae was identified. Ixodes ventalloi female and both I. ricinus tested positive in the screening PCR, but the sequencing for the identification of the Rickettsia sp. failed.

Molecular surveillance of microbial agents from cattle-attached and questing ticks from livestock agroecosystems of Antioquia, Colombia

Ticks are obligate ectoparasites and vectors of pathogens affecting health, agriculture, and animal welfare. This study collected ticks from the cattle and questing ticks of 24 Magdalena Medio Antioquia region cattle farms. Genomic DNA was extracted from the specimens (individual or pools) of the 2088 adult ticks collected from cattle and 4667 immature questing ticks collected from pastures. The molecular detection of Babesia, Anaplasma, Coxiella and Rickettsia genera was performed by polymerase chain reaction amplification and subsequent DNA sequencing. In a total of 6755 Rhipicephalus microplus DNA samples, Anaplasma marginale was the most detected with a frequency of 2% (Confidence Interval- CI 1.68-2.36), followed by Babesia bigemina with 0.28% (CI 0.16-0.44), Coxiella spp. with 0.15% (CI 0.07-0.27), and Rickettsia spp. with 0.13% (CI 0.06-0.25). Molecular analysis of the DNA sequences obtained from the tick samples revealed the presence of Coxiella-like endosymbiont and R. felis. These results demonstrated the diversity of microorganisms present in R. microplus ticks predominantly associated with cattle and questing ticks from livestock agroecosystems, suggesting their role as reservoirs and potential biological vectors of these microorganisms on the studied sites. Also, it emphasizes the need to combine acarological surveillance with clinical diagnoses and control strategies on regional and national levels.

Diversity of Rickettsia spp. in ticks from wild mammals of Morocco and Mauritania

Ticks are known as vectors and reservoirs of rickettsiae and, wildlife vertebrate hosts as suitable dispersers of ticks contributing to the life cycle of rickettsial agents in nature. In the herein study, the presence of rickettsiae was investigated in ticks from wild mammals (Gerbillus and Jaculus, Vulpes rueppellii, Canis anthus, Felis lybica and Felis margarita) in Mauritania and Morocco. Morphological and molecular analysis of ticks allowed their identification as Rhipicephalus sanguineus sensu lato and Hyalomma impeltatum. A total of 126 partially engorged adult ticks, collected from 40 animals, were screened for the presence of rickettsial DNA by conventional PCR targeting the ompB gene, followed by ompA and gltA targets and bidirectional sequencing. As a result of the sequence analyses, that at least three different species of pathogenic spotted fever group rickettsiae were detected. Rickettsia parkeri-like was detected in a R. sanguineus s.l. (n=1) collected from an African wildcat from Morocco. Rickettsia aeschlimannii was detected in a H. impeltatum (n=1) collected from a gerbil rodent. Rickettsia massiliae was detected in R. sanguineus s.l. ticks (n=5) collected from two Ruppells' foxes. The herein study demonstrates that pathogenic Rickettsia species are circulating in Morocco and Mauritania wildlife.

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

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

Rickettsia communities and their relationship with tick species within and around the national park of Iguaçu, Brazil

We report Rickettsia species from 2,334 ticks collected from environment (1,939 ticks) and animals (395 ticks) in the largest inland fragment of the Atlantic rainforest of southern Brazil and its fragments. Additionally, the DNA infection rates of Amblyomma ovale tick populations in the Neotropics with Rickettsia bellii and Rickettsia parkeri strain Atlantic rainforest were calculated using data from scientific publications, and their correlation was evaluated. From 11 tick species Rickettsia DNA was detected in seven (Amblyomma brasiliense, Amblyomma coelebs, Amblyomma incisum, Amblyomma longirostre, A. ovale, Haemaphysalis juxtakochi, Ixodes fuscipes) and was not detected in four species (Amblyomma dubitatum, Ixodes loricatus, Rhipicephalus microplus and Rhipicephalus sanguineus sensu lato). DNA of five Rickettsia species was detected (R. bellii, Rickettsia amblyommatis, Rickettsia rhipicephali, Rickettsia felis and Rickettsia sp. Aragaoi). To determine the prevalence of Rickettsia DNA positivity according to vector species, ticks were processed individually or in pools of 2-10 individuals (samples). The most prevalent Rickettsia species was R. bellii, found in 112 samples, followed by R. amblyommatis, R. rhipicephali, R. felis and Rickettsia sp. Aragaoi, found in 16, five, two and one sample, respectively. Rickettsia bellii DNA was found in five tick species with the highest infection rate in A. ovale and A. brasiliense. Absence of R. parkeri strain Atlantic rainforest in A. ovale ticks was an unexpected result. Furthermore, a negative correlation was identified between the infection rates (DNA) of R. bellii and/or R. parkeri strain Atlantic rainforest within A. ovale tick populations in the Neotropics. Putting together current knowledge, it can be proposed that, within natural settings, the diversity of rickettsiae and ticks creates a buffering effect on the overgrowth of rickettsiae and episodes of bacteremia in the hosts.

First isolation of Rickettsia amblyommatis from Amblyomma mixtum in Colombia

BACKGROUND

Rickettsiae are obligate intracellular Gram-negative bacteria that are the causative agent of rickettsioses and are spread to vertebrate hosts by arthropods. There are no previous reports of isolation of Rickettsia amblyommatis for Colombia.

METHODS

A convenience sampling was executed in three departments in Colombia for direct collection of adult ticks on domestic animals or over vegetation. Ticks were screened for the presence of Rickettsia spp. by real-time polymerase chain reaction (qPCR) amplifying the citrate synthase gene (gltA), and the positive sample was processed for isolation and further molecular characterization by conventional PCR. The absolute and relative frequencies were calculated for several tick species variables. All products from conventional PCR were further purified and sequenced by the Sanger technique. Representative sequences of 18 Rickettsia species were downloaded from GenBank. Consensus phylogenetic trees were constructed for the gltA, ompB, ompA, and htrA genes with 1000 replicates, calculating bootstrap values through the maximum likelihood method and the generalized time reversible substitution model in the MEGA 7.0 software program.

RESULTS

One female Amblyomma mixtum collected on vegetation was amplified by qPCR (gltA), indicating a frequency of 1.6% (1/61) for Rickettsia spp.

INFECTION

Sequence analysis of a rickettsial isolate from this tick in BLASTn showed 100% identity with gltA (340 base pairs [bp]), 99.87% for ompB (782 bp), 98.99% for htrA (497 bp), and 100% for ompA (488 bp) to R. amblyommatis. Concatenated phylogenetic analysis confirmed these findings indicating that the isolate is grouped with other sequences of Amblyomma cajennense complex from Panama and Brazil within the R. amblyommatis clade.

CONCLUSIONS

This paper describes the isolation and early molecular identification of a R. amblyommatis strain from A. mixtum in Colombia.

History and Current Status of Mediterranean Spotted Fever (MSF) in the Crimean Peninsula and Neighboring Regions along the Black Sea Coast

Mediterranean spotted fever (MSF) is a tick-borne rickettsiosis caused by Rickettsia conorii subspecies conorii and transmitted to humans by Rhipicephalus sanguineus ticks. The disease was first discovered in Tunisia in 1910 and was subsequently reported from other Mediterranean countries. The first cases of MSF in the former Soviet Union were detected in 1936 on the Crimean Peninsula. This review summarizes the historic information and main features of MSF in that region and contemporary surveillance and control efforts for this rickettsiosis. Current data pertinent to the epidemiology of the disease, circulation of the ticks and distribution of animal hosts are discussed and compared for each of the countries in the Black Sea basin where MSF occurs.

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

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

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.

Molecular detection of Rickettsia spp. in wild ungulates and their ticks in Mediterranean areas of southwestern Spain

Wildlife is an important reservoir of zoonotic pathogens. The objective of the present study was to assess the importance of wild ungulates in the epidemiology of Rickettsia spp. Ticks and spleen samples were collected from 262 red deer (Cervus elaphus) and 83 wild boar (Sus scrofa) hunted in southwestern Spain over a 5-year period. DNA was extracted from tick pools (n = 191) and spleens (n = 345), and two nested PCR assays targeting the rOmpA and rOmpB genes were used to detect Rickettsia DNA. Five tick species were identified (Hyalomma lusitanicum, Dermacentor marginatus, Ixodes ricinus, Rhipicephalus bursa and Haemaphysalis sulcata). Rickettsia DNA was detected in 31 (16.2%) tick pools and two red deer spleen samples (0.8%). Four validated Rickettsia species (R. slovaca, R. monacensis, R. helvetica and R. raoultii), one uncultivated species (Candidatus R. rioja) and two uncharacterized Rickettsia spp. were detected in ticks. R. helvetica and R. slovaca were also detected in spleen samples from red deer. The overall prevalence in ungulate spleen samples was lower than in tick pools suggesting that these ungulates do not play a major role in the transmission of Rickettsia spp. However, their importance as spreaders of positive ticks cannot be ruled out. The results present a challenge for the veterinary and public health communities since most of the Rickettsia spp. detected are pathogenic. Furthermore, the new Rickettsia species could be potential pathogens. For these reasons, identifying Rickettsia species present in ticks and wildlife is of particular interest to clarify their sylvatic cycle and establish appropriate control measures.

Pathogenic Rickettsia, Anaplasma, and Ehrlichia in Rhipicephalus microplus ticks collected from cattle and laboratory hatched tick larvae

BACKGROUND

The order Rickettsiales contains a group of vector-borne gram-negative obligate intracellular bacteria, which often cause human emerging infectious diseases and economic losses for dairy and meat industries. The purpose of this study is to investigate the distribution of the pathogens including Rickettsia spp., Anaplasma spp., and Ehrlichia spp. in the order Rickettsiales in ticks from Yueyang, a prefecture-level city of Hunan Province in Sothern China, and assess the potentiality of transovarial transmission of these rickettsial organisms.

METHODS

Ticks were collected from cattle in a farm in Yueyang City and the tick DNA was used as template to amplify the htrA, rrs, gltA, ompA and ompB genes of Rickettsia as well as rrs and groEL genes of Anaplasma and Ehrlichia.

RESULTS

All ticks (465) collected were the cattle tick, Rhipicephalus microplus. PCR showed the minimum infection rate (MIR) was 1.5% (7/465) for Candidatus Rickettsia xinyangensis, 1.9% (9/465) for C. Anaplasma boleense, 1.3% (6/465) for Anaplasma platys, 0.6% (3/465) for A. marginale, and 1.17% (2/465) for each of A. bovis, Ehrlichia minasensis, and a non-classified Ehrlichia sp. A human pathogen, C. Rickettsia xinyangensis and A. platys were detected in 100% (3/3) and 33.3% (2/6) laboratory-hatched larval pools from infected females respectively.

CONCLUSION

Our study revealed a diversity of pathogenic rickettsial species in R. microplus ticks from Hunan Province suggesting a threat to people and animals in China. This study also provided the first molecular evidence for the potential transovarial transmission of C. Rickettsia xinyangensis and A. platys in R. microplus, indicating that R. microplus may act as the host of these two pathogens.

Disparate dynamics of pathogen prevalence in Ixodes ricinus and Dermacentor reticulatus ticks occurring sympatrically in diverse habitats

Ixodes ricinus and Dermacentor reticulatus ticks are important reservoirs and vectors of pathogens. The aim of the present study was to investigate the dynamic of the prevalence and genetic diversity of microorganisms detected in these tick species collected from two ecologically diverse biotopes undergoing disparate long-term climate condition. High-throughput real time PCR confirmed high prevalence of microorganisms detected in sympatrically occurring ticks species. D. reticulatus specimens were the most often infected with Francisella-like endosymbiont (FLE) (up to 100.0%) and Rickettsia spp. (up to 91.7%), while in case of I. ricinus the prevalence of Borreliaceae spirochetes reached up to 25.0%. Moreover, pathogens belonging to genera of Bartonella, Anaplasma, Ehrlichia and Babesia were detected in both tick species regardless the biotope. On the other hand, Neoehrlichia mikurensis was conformed only in I. ricinus in the forest biotope, while genetic material of Theileria spp. was found only in D. reticulatus collected from the meadow. Our study confirmed significant impact of biotope type on prevalence of representatives of Borreliaceae and Rickettsiaceae families. The most common co-infection detected in D. reticulatus was Rickettsia spp. + FLE, while Borreliaceae + R. helvetica was the most common in I. ricinus. Additionally, we found significant genetic diversity of R. raoultii gltA gene across studied years, however such relationship was not observed in ticks from studied biotopes. Our results suggest that ecological type of biotope undergoing disparate long-term climate conditions have an impact on prevalence of tick-borne pathogens in adult D. reticulatus and I. ricinus.

The inoculation eschar of Rickettsia parkeri rickettsiosis in Brazil: Importance and cautions

Two well characterized tick-borne rickettsioses occur in Brazil. Rickettsia rickettsii caused spotted-fever, transmitted by Amblyomma sculptum and Amblyomma aureolatum, is a severe disease with a high case-fatality rate in the southeastern region of the country. Rickettsia parkeri strain Atlantic rainforest infections transmitted by adult Amblyomma ovale ticks cause a milder non-lethal febrile disease with an eschar (necrosis) at the tick bite site. Clinical diagnosis of rickettsiosis is challenging, particularly during the early stages of the illness when signs and symptoms are non-specific. Since eschar at the tick bite site has emerged as the main clinical feature of mild R. parkeri infections and used to differentiate it from severe R. rickettsii infection, its proper recognition, distinction from other tick bite lesions, and boundaries as a clinical tool must be highlighted. Of importance, eschars induced by Rickettsia must be differentiated from dermatoses caused by other tick-borne skin infections as well from lesions caused by the tick bite itself. We herein highlight information on eschar in rickettsial diseases in Brazil and discuss the need for further research on its clinical relevance and application in the diagnosis of spotted fever caused by R. parkeri strain Atlantic rainforest. In particular, we draw attention to diagnosis of other febrile diseases in the presence of concomitant tick bites.

Rickettsia amblyommatis in Ticks: A Review of Distribution, Pathogenicity, and Diversity

Rickettsia amblyommatis is a potentially pathogenic species of Rickettsia within the spotted fever group vectored by ticks. While many studies have been published on this species, there is debate over its pathogenicity and the inhibitory role it plays in diagnosing illnesses caused by other spotted fever group Rickettsia species. Many publications have recorded the high infection prevalence of R. amblyommatis in tick populations at a global scale. While this species is rather ubiquitous, questions remain over the epidemiological importance of this possible human pathogen. With tick-borne diseases on the rise, understanding the exact role that R. amblyommatis plays as a pathogen and inhibitor of infection relative to other tick-borne pathogens will help public health efforts. The goal of this review was to compile the known literature on R. amblyommatis, review what we know about its geographic distribution, tick vectors, and pathogenicity, assess relatedness between various international strains from ticks by phylogenetic analysis and draw conclusions regarding future research needed.

Rickettsia spp. in Ticks of South Luangwa Valley, Eastern Province, Zambia

Ticks are important vectors for Rickettsia spp. belonging to the Spotted Fever Group responsible for causing Rickettsiosis worldwide. Rickettsioses pose an underestimated health risk to tourists and local inhabitants. There is evidence of the presence of Rickettsia spp. in Zambia, however there is limited data. A total of 1465 ticks were collected in 20 different locations from dogs and cattle including one cat. Ticks were identified by morphological features or by sequencing of the 16S mitochondrial rRNA gene. Individual ticks were further tested for rickettsiae using a pan-Rickettsia real-time-PCR. Rickettsia species in PCR-positive ticks were identified by sequencing the 23S-5S intergenic spacer region or partial ompA gene, respectively. Seven tick species belonging to three different tick genera were found, namely: Amblyomma variegatum, Rhipicephalus appendiculatus, Rhipicephalus (Boophilus) microplus, Rhipicephalus simus, Rhipicephalus sanguineus, Rhipicephalus zambesiensis and Haemaphysalis elliptica. Out of the 1465 ticks collected, 67 (4.6%) tested positive in the pan-Rickettsia PCR. This study provides detailed data about the presence of Rickettsia species in South Luangwa Valley, Eastern Province, Zambia for the first time. High prevalence of Rickettsia africae in Amblyomma variegatum was found, which indicates the potential risk of infection in the investigated area. Furthermore, to our best knowledge, this is the first time Rickettsia massiliae, a human pathogen causing spotted fever, has been detected in Zambia.

Molecular Detection of Rickettsia and Other Bacteria in Ticks and Birds in an Urban Fragment of Tropical Dry Forest in Magdalena, Colombia

Birds are important hosts in the life cycle of some species of ticks. In Colombia, there are few eco-epidemiological studies of tick-borne diseases; the existing ones have been focused on areas where unusual outbreaks have occurred. This study describes the identification of ticks collected from birds and vegetation, and the detection of bacteria in those ticks and in blood samples from birds in an urban fragment of tropical dry forest in the department of Magdalena, Colombia. Bird sampling was carried out monthly in 2021, and 367 birds, distributed among 41 species, were captured. All collected ticks were identified as Amblyomma sp. or Amblyomma dissimile. The presence of rickettsiae in ticks collected from birds was evaluated by molecular analysis of the gltA, ompA and sca1 genes. 16S rRNA meta-taxonomy was used to evaluate rickettsiae in ticks collected from vegetation and in blood samples from birds. The presence of the species "Candidatus Rickettsia colombianensi" was detected in ticks from birds. Bacteria of the family Rickettsiacea was the most abundant in ticks collected from vegetation. Bacteria of the families Staphylococcaceae, Comamonadaceae and Pseudomonadaceae were prevalent in the samples of blood from birds. Rickettsia spp. was also detected in low abundance in some of the bird blood samples.

Coinfection of Two Rickettsia Species in a Single Tick Species Provides New Insight into Rickettsia-Rickettsia and Rickettsia-Vector Interactions

Rickettsiae are obligate intracellular bacteria that can cause life-threatening illnesses. There is an ongoing debate as to whether established infections by one Rickettsia species preclude the maintenance of the second species in ticks. Here, we identified two Rickettsia species in inoculum from Haemaphysalis montgomeryi ticks and subsequently obtained pure isolates of each species by plaque selection. The two isolates were classified as a transitional group and spotted fever group rickettsiae and named Rickettsia hoogstraalii str CS and Rickettsia rhipicephalii str EH, respectively. The coinfection of these two Rickettsia species was detected in 25.6% of individual field-collected H. montgomeryi. In cell culture infection models, R. hoogstraalii str CS overwhelmed R. rhipicephalii str EH with more obvious cytopathic effects, faster plaque formation, and increased cellular growth when cocultured, and R. hoogstraalii str CS seemed to polymerize actin tails differently from R. rhipicephalii str EH in vitro. This work provides a model to investigate the mechanisms of both Rickettsia-Rickettsia and Rickettsia-vector interactions. IMPORTANCE The rickettsiae are a group of obligate intracellular Gram-negative bacteria that include human pathogens causing an array of clinical symptoms and even death. There is an important question in the field, that is whether one infection can block the superinfection of other rickettsiae. This work demonstrated the coinfection of two Rickettsia species in individual ticks and further highlighted that testing the rickettsial competitive exclusion hypothesis will undoubtedly be a promising area as methods for bioengineering and pathogen biocontrol become amenable for rickettsiae.

Capybara Ticks and the Urban Context of Spotted Fever in Brazil: An Overview

Spotted fever is caused by Rickettsia rickettsii and is transmitted through tick’s saliva. Humans, ticks, and capybaras (Hydrochoerus hydrochaeris) are often coexisting in environments that favor the spread of Brazilian spotted fever (BSF). Although capybaras do not transmit R. rickettsii, they can amplify these bacteria among tick vector populations, playing a significant role in the one health approach and epidemiology of the disease. Urban populations of capybaras have increased, especially in Southeast Brazil, as well as the number of cases and lethality of BSF have increased in the country since the 1980s. This expansion is mainly determined by the availability of food and the absence of predators. Thus, urban areas, including parks and university campuses, provide an abundance of food and protection against predators, ensuring the multiplication of the species and increasing the risk of transmission to humans due to the proximity of man with animals in the urban environment. Therefore, this chapter aims to address aspects of spotted fever, considering the many dimensions of the species involved, contributing to public strategies and policies.

A forty-year review of Rocky Mountain spotted fever cases in California shows clinical and epidemiologic changes

Rocky Mountain spotted fever (RMSF) is a life-threatening tick-borne disease documented in North, Central, and South America. In California, RMSF is rare; nonetheless, recent fatal cases highlight ecological cycles of the two genera of ticks, Dermacentor and Rhipicephalus, known to transmit the disease. These ticks occur in completely different habitats (sylvatic and peridomestic, respectively) resulting in different exposure risks for humans. This study summarizes the demographic, exposure, and clinical aspects associated with the last 40 years of reported RMSF cases to the California Department of Public Health (CDPH). Seventy-eight RMSF cases with onsets from 1980 to 2019 were reviewed. The incidence of RMSF has risen in the last 20 years from 0.04 cases per million to 0.07 cases per million (a two-fold increase in reports), though the percentage of cases that were confirmed dropped significantly from 72% to 25% of all reported cases. Notably, Hispanic/Latino populations saw the greatest rise in incidence. Cases of RMSF in California result from autochthonous and out-of-state exposures. During the last 20 years, more cases reported exposure in Southern California or Mexico than in the previous 20 years. The driver of these epidemiologic changes is likely the establishment and expansion of Rhipicephalus sanguineus sensu lato ticks in Southern California and on-going outbreaks of RMSF in northern Mexico. Analysis of available electronically reported clinical data from 2011 to 2019 showed that 57% of reported cases presented with serious illness requiring hospitalization with a 7% mortality. The difficulty in recognizing RMSF is due to a non-specific clinical presentation; however, querying patients on the potential of tick exposure in both sylvatic and peridomestic environments may facilitate appropriate testing and treatment.

Relevance of Spatial and Temporal Trends in Nymphal Tick Density and Infection Prevalence for Public Health and Surveillance Practice in Long-Term Endemic Areas: A Case Study in Monmouth County, NJ

Tick-borne diseases are a growing public health problem in the United States, and the US northeast has reported consistently high case rates for decades. Monmouth County, New Jersey, was one of the earliest jurisdictions to report Lyme disease cases in 1979 and reports several hundred cases per year nearly 40 yr later. In the time since, however, tick-borne health risks have expanded far beyond Lyme disease to include a variety of other bacterial pathogens and viruses, and additional vectors, necessitating a continually evolving approach to tick surveillance. In 2017, Monmouth County initiated an active surveillance program targeting sites across three ecological regions for collection of Ixodes scapularis Say (Acari: Ixodidae) and Amblyomma americanum L. (Acari: Ixodidae) as well as testing via qPCR for associated bacterial pathogens. During the first five years of this program (2017-2021), we report high levels of spatiotemporal variability in nymphal density and infection prevalence in both species, limiting the granularity with which human risk can be predicted from acarological data. Nonetheless, broader patterns emerged, including an ongoing trend of A. americanum dominance, risks posed by Borrelia miyamotoi, and the frequency of coinfected ticks. We present some of the first county-level, systematic surveillance of nymphal A. americanum density and infection prevalence in the northeastern US. We also documented a temporary decline in Borrelia burgdorferi that could relate to unmeasured trends in reservoir host populations. We discuss the implications of our findings for tick-borne disease ecology, public health communication, and tick surveillance strategies in endemic areas.

Possible Association between Selected Tick-Borne Pathogen Prevalence and Rhipicephalus sanguineus sensu lato Infestation in Dogs from Juarez City (Chihuahua), Northwest Mexico–US Border

Tick-borne bacterial pathogens (TBBPs) show a worldwide distribution and represent a great impact on public health. The brown dog tick (Rhipicephalus sanguineus) is a vector of several pathogens that affect dogs and sometimes humans as well. In addition, TBBPs represent a diagnostic challenge and imply financial resources and medical treatment for long periods of time. In the present study, R. sanguineus s. l. was identified as the main tick species naturally parasitizing dogs that inhabit. Juárez City, Chihuahua, in the Paso del Norte region, Mexico–US Border, representing 99.8% of the cases. Additionally, an end-point PCR was performed to search for whether pathogens in R. sanguineus s. l. can transmit in DNA extracted from ticks and dog blood samples. This is the first molecular detection of Rickettsia rickettsi infecting domestic dogs in Mexico; however, other pathogens were also identified, such as Ehrlichia canis and Anaplasma platys in both ticks and dog blood samples, while Anaplasma phagocytophilum was identified only in dog blood samples. Moreover, co-detection in tick pools and co-infection in the analyzed dog blood samples could be found. Similarly, this research showed that dogs were found mostly parasitized by adult female ticks, increasing the possibility of transmission of E. canis.

Prevention of tick-borne diseases: challenge to recent medicine

Abstract

Ticks represent important vectors and reservoirs of pathogens, causing a number of diseases in humans and animals, and significant damage to livestock every year. Modern research into protection against ticks and tick-borne diseases focuses mainly on the feeding stage, i.e. the period when ticks take their blood meal from their hosts during which pathogens are transmitted. Physiological functions in ticks, such as food intake, saliva production, reproduction, development, and others are under control of neuropeptides and peptide hormones which may be involved in pathogen transmission that cause Lyme borreliosis or tick-borne encephalitis. According to current knowledge, ticks are not reservoirs or vectors for the spread of COVID-19 disease. The search for new vaccination methods to protect against ticks and their transmissible pathogens is a challenge for current science in view of global changes, including the increasing migration of the human population.

Highlights

• Tick-borne diseases have an increasing incidence due to climate change and increased human migration

• To date, there is no evidence of transmission of coronavirus COVID-19 by tick as a vector

• To date, there are only a few modern, effective, and actively- used vaccines against ticks or tick-borne diseases

• Neuropeptides and their receptors expressed in ticks may be potentially used for vaccine design

Comparing scapular morphology of Amblyomma sculptum and Amblyomma dubitatum nymphs allows a fast and practical differential diagnosis of ticks in highly infested areas with dominance of these two species

Rickettsia rickettsii infection causes the highest human fatality rate among all Rickettsia species of the world and is endemic in Southeast Brazil. In this part of the country most human spotted fever cases are related to unnaturally high populations of ticks, usually a mix of two species, Amblyomma dubitatum Neumann and Amblyomma sculptum Berlese and their local host, capybara (Hydrochoerus hydrochaeris). At the same time, an increase in the number of SF notifications as well as its urbanization was observed, and a better characterization of disease epidemiology is mandatory for control measures and to halt its expansion. It was recently noticed in southeast Brazil that SF endemic areas were characterized by overgrowth populations of A. sculptum and decreased populations of A. dubitatum. Hence, characterization of areas with potential to endemicity, eco-epidemiological studies and control measures may rely on the evaluation of A. sculptum/A. dubitatum rate. However, in potentially endemic scenarios, discriminating the two tick species, particularly the nymphs considered the main vector stage, is a challenge in face of several hundreds to thousands of ticks that should be examined for quantitative studies. We herein present additional morphological features to an existing identification key for Amblyomma nymphs that considerably diminishes the labor to distinguish nymphs of these two tick species. Specifically, the oval-shaped scutum of A. dubitatum and a conspicuous scapula of A. sculptum are prominent discriminating features.

Near-term forecasting of companion animal tick paralysis incidence: An iterative ensemble model

Tick paralysis resulting from bites from Ixodes holocyclus and I. cornuatus is one of the leading causes of emergency veterinary admissions for companion animals in Australia, often resulting in death if left untreated. Availability of timely information on periods of increased risk can help modulate behaviors that reduce exposures to ticks and improve awareness of owners for the need of lifesaving preventative ectoparasite treatment. Improved awareness of clinicians and pet owners about temporal changes in tick paralysis risk can be assisted by ecological forecasting frameworks that integrate environmental information into statistical time series models. Using an 11-year time series of tick paralysis cases from veterinary clinics in one of Australia's hotspots for the paralysis tick Ixodes holocyclus, we asked whether an ensemble model could accurately forecast clinical caseloads over near-term horizons. We fit a series of statistical time series (ARIMA, GARCH) and generative models (Prophet, Generalised Additive Model) using environmental variables as predictors, and then combined forecasts into a weighted ensemble to minimise prediction interval error. Our results indicate that variables related to temperature anomalies, levels of vegetation moisture and the Southern Oscillation Index can be useful for predicting tick paralysis admissions. Our model forecasted tick paralysis cases with exceptional accuracy while preserving epidemiological interpretability, outperforming a field-leading benchmark Exponential Smoothing model by reducing both point and prediction interval errors. Using online particle filtering to assimilate new observations and adjust forecast distributions when new data became available, our model adapted to changing temporal conditions and provided further reduced forecast errors. We expect our model pipeline to act as a platform for developing early warning systems that can notify clinicians and pet owners about heightened risks of environmentally driven veterinary conditions.

The Impact of Deforestation, Urbanization, and Changing Land Use Patterns on the Ecology of Mosquito and Tick-Borne Diseases in Central America

Central America is a unique geographical region that connects North and South America, enclosed by the Caribbean Sea to the East, and the Pacific Ocean to the West. This region, encompassing Belize, Costa Rica, Guatemala, El Salvador, Honduras, Panama, and Nicaragua, is highly vulnerable to the emergence or resurgence of mosquito-borne and tick-borne diseases due to a combination of key ecological and socioeconomic determinants acting together, often in a synergistic fashion. Of particular interest are the effects of land use changes, such as deforestation-driven urbanization and forest degradation, on the incidence and prevalence of these diseases, which are not well understood. In recent years, parts of Central America have experienced social and economic improvements; however, the region still faces major challenges in developing effective strategies and significant investments in public health infrastructure to prevent and control these diseases. In this article, we review the current knowledge and potential impacts of deforestation, urbanization, and other land use changes on mosquito-borne and tick-borne disease transmission in Central America and how these anthropogenic drivers could affect the risk for disease emergence and resurgence in the region. These issues are addressed in the context of other interconnected environmental and social challenges.

Microbiomes of Blood-Feeding Arthropods: Genes Coding for Essential Nutrients and Relation to Vector Fitness and Pathogenic Infections. A Review

BACKGROUND

Blood-feeding arthropods support a diverse array of symbiotic microbes, some of which facilitate host growth and development whereas others are detrimental to vector-borne pathogens. We found a common core constituency among the microbiota of 16 different arthropod blood-sucking disease vectors, including Bacillaceae, Rickettsiaceae, Anaplasmataceae, Sphingomonadaceae, Enterobacteriaceae, Pseudomonadaceae, Moraxellaceae and Staphylococcaceae. By comparing 21 genomes of common bacterial symbionts in blood-feeding vectors versus non-blooding insects, we found that certain enteric bacteria benefit their hosts by upregulating numerous genes coding for essential nutrients. Bacteria of blood-sucking vectors expressed significantly more genes (p < 0.001) coding for these essential nutrients than those of non-blooding insects. Moreover, compared to endosymbionts, the genomes of enteric bacteria also contained significantly more genes (p < 0.001) that code for the synthesis of essential amino acids and proteins that detoxify reactive oxygen species. In contrast, microbes in non-blood-feeding insects expressed few gene families coding for these nutrient categories. We also discuss specific midgut bacteria essential for the normal development of pathogens (e.g., Leishmania) versus others that were detrimental (e.g., bacterial toxins in mosquitoes lethal to Plasmodium spp.).

Molecular detection of Rickettsia amblyommatis and Rickettsia parkeri in ticks collected from wild pigs in Campeche, Mexico

Tick-borne rickettsioses are caused at least by 15 species of Rickettsia of the Spotted fever group, which represent a major emerging and re-emerging public health problem worldwide. Some of these microorganisms have complex cycles involving the interaction of multiple species of ticks and wild and domestic mammals. Rickettsia infection was investigated in ticks collected from wild pigs at six localities in southeastern Mexico. We collected and tested 196 ticks belonging to four species, including Amblyomma maculatum, Amblyomma mixtum, Amblyomma ovale and Riphicephalus microplus, from 13 of 20 (65%) wild pigs sampled. Overall, Rickettsia DNA was detected in 13.8% of ticks tested (10 ♂ and 17 ♀). Of the 27 Rickettsia-positive ticks, six were A. maculatum, and 21 A. mixtum. Sequencing and phylogenetic analysis of the gltA and ompB genes revealed the presence of Rickettsia parkeri sensu stricto in one female A. maculatum and Rickettsia amblyommatis in five A. maculatum (2 ♂, 3 ♀) and 21 A. mixtum ticks (8 ♂, 13 ♀). The finding of two rickettsial agents in ticks collected from a wild pig population that is regularly captured and kept in captivity or hunted as a source of food raises concern about potential disease transmission to humans and domestic animals. However, more investigations are needed to further understand the ecology of Rickettsia species in free-ranging animals and their implications for human health.

Impact of a Severe Rocky Mountain Spotted Fever Case on Treatment Practices at an Academic Institution Within a Nonendemic Area

INTRODUCTION

Rocky Mountain spotted fever (RMSF) is a bacterial disease associated with morbidity and mortality when untreated. The primary study objectives are to describe clinician diagnostic and treatment practices in a nonendemic area after the occurrence of an unrecognized severe pediatric presumed RMSF case (index case). We hypothesized that inpatient diagnostic testing frequency and initiation of empiric treatment will increase after the index case.

METHODS

We performed a retrospective chart review of patients aged less than 18 y evaluated for RMSF at Penn State Hershey Children's Hospital between 2010 and 2019. We divided the study population into 2 groups (preindex and postindex) and evaluated patient characteristics, RMSF testing completion, and timing of doxycycline administration.

RESULTS

Fifty-four patients (14 [26%] preindex and 40 [74%] postindex) were included. Age (median [25^th percentile, 75^th percentile]) decreased from 14.5 y (8.6, 16) preindex to 8.3 y (3.6, 14) postindex. Twelve (86%) preindex and 31 (78%) postindex patients received empiric doxycycline (P=0.70). Four years after the index case, a decrease in empiric and urgent initiation of doxycycline administration was noted. One case of severe RMSF was diagnosed 4 y after the index case.

CONCLUSIONS

Our study found that inpatient RMSF testing increased after the index case, but not all patients received empiric treatment. This may represent an underappreciation of RMSF severity even after a recent devastating case. We suggest that when severe rare but possibly reversible diseases, such as RMSF occur, all clinicians are educated on the diagnostic and treatment approach to reduce the morbidity and mortality risk.

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.

Biodiversity of Potential Vectors of Rickettsiae and Epidemiological Mosaic of Spotted Fever in the State of Paraná, Brazil

Spotted Fever Rickettsioses (SFR) are diseases caused by bacteria of the genus Rickettsia, and are transmitted mainly by ticks. Its eco-epidemiological scenarios vary spatially, and may also vary over time due to environmental changes. It is the main disease transmitted by ticks to humans in Brazil, with the state of Paraná (PR) having the sixth highest number of notified incidences in the country. However, information is lacking regarding the SFR disease cycles at likely infection sites within PR. During case investigations or environmental surveillance in PR for SFR, 28,517 arthropods were collected, including species known or potentially involved in the SFR cycles, such as Amblyomma sculptum, Amblyomma aureolatum, Amblyomma ovale, Amblyomma dubitatum, Amblyomma parkeri, Ctenocephalides felis felis, and Rhipicephalus sanguineus sensu lato. From these Rickettsia asembonensis, Rickettsia bellii, Rickettsia felis, Rickettsia parkeri strain Atlantic Rainforest and Candidatus Rickettsia paranaensis were detected. Ectoparasite abundance was found to be related with specific hosts and collection environments. Rickettsiae circulation was observed for 48 municipalities, encompassing 16 Health Regions (HR). As for socio-demographic and assistance indicators, circulation occurred largely in the most urbanized HR, with a higher per capita Gross Domestic Product, lower Family Health Strategy coverage, and with a higher ratio of beds in the Unified Health System per thousand inhabitants. For environmental variables, circulation occurred predominantly in HR with a climatic classified as “subtropical with hot summers” (Cfa), and with forest type phytogeographic formations. In terms of land use, circulation was commonest in areas with agriculture, pasture and fields and forest cover. Rickettsiae were circulating in almost all hydrographic basins of PR state. The results of this study provide the first descriptive recognition of SFR in PR, as well as outlining its eco-epidemiological dynamics. These proved to be quite heterogeneous, and analyzed scenarios showed characteristics strongly-associated with the outbreaks, with cases presenting clinical variation in space, so illustrating the complexity of scenarios in PR state. Due to the diversity of the circumstances surrounding SFR infections in PR, public health initiatives are necessary to foster a better understanding of the dynamics and factors effecting vulnerability to SFR in this Brazilian state.

Diversity of rickettsiae in domestic, synanthropic, and sylvatic mammals and their ectoparasites in a spotted fever-epidemic region at the western US-Mexico border

Over one hundred cases of human rickettsiosis, many fatal, are reported annually across the US-Mexico transboundary region, representing a likely undercount. Although cases are often attributed to Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, multiple other Rickettsia pathogens are present in North America. We conducted multiple-host surveillance of domestic, synanthropic, and sylvatic mammals and their ectoparasites to investigate the ecology of Rickettsia species in this region. A total of 499 mammals, including 83 dogs, 23 wild carnivores, five lagomorphs, and 388 rodents were sampled, and 413 fleas and 447 ticks belonging to 15 and 4 species, respectively, were collected during 2017 and 2018. We detected Rickettsia spp. DNA in one blood sample of coyote (Canis latrans), 11 ear tissues of rodents (10.6%), and 79 ectoparasites (9.5%). Of the 64 Rickettsia-positive fleas, 54 were Echidnophaga gallinacea and 10 were Pulex simulans, while of the 15 ticks, 11 were Rhipicephalus sanguineus s.l. and four Ixodes pacificus. The DNA sequence alignment of gltA and ompB regions revealed one and ten genetic variants of Rickettsia spp., respectively. These variants were clustered in clades of zoonotic species (R. felis, R. massiliae, R. parkeri, R. rickettsii, and R. typhi) and organisms of unknown pathogenic significance (R. asembonensis and Candidatus Rickettsia tarasevichiae). The finding of a coyote infected with R. rickettsii and the multiple zoonotic SFG rickettsial agents in the study area suggest that: 1) wild canids could serve as an amplifying host for RMSF, an alternate host for Rh. sanguineus s.l. ticks, and a means to spread infection and ticks over large areas; and 2) at least some of the human rickettsiosis cases attributed to R. rickettsii could be caused by other Rickettsia species. This study strongly supports the importance of multiple-host and vector eco-epidemiological studies and the One Health approach to better understand disease in a RMSF-epidemic region.

Scoping review of distribution models for selected Amblyomma ticks and rickettsial group pathogens

The rising prevalence of tick-borne diseases in humans in recent decades has called attention to the need for more information on geographic risk for public health planning. Species distribution models (SDMs) are an increasingly utilized method of constructing potential geographic ranges. There are many knowledge gaps in our understanding of risk of exposure to tick-borne pathogens, particularly for those in the rickettsial group. Here, we conducted a systematic scoping review of the SDM literature for rickettsial pathogens and tick vectors in the genus Amblyomma. Of the 174 reviewed articles, only 24 studies used SDMs to estimate the potential extent of vector and/or pathogen ranges. The majority of studies (79%) estimated only tick distributions using vector presence as a proxy for pathogen exposure. Studies were conducted at different scales and across multiple continents. Few studies undertook original data collection, and SDMs were mostly built with presence-only datasets from public database or surveillance sources. The reliance on existing data sources, using ticks as a proxy for disease risk, may simply reflect a lag in new data acquisition and a thorough understanding of the tick-pathogen ecology involved.

Rickettsia spp. in rodent-attached ticks in Estonia and first evidence of spotted fever group Rickettsia species Candidatus Rickettsia uralica in Europe

BACKGROUND

Rickettsia spp. are human pathogens that cause a number of diseases and are transmitted by arthropods, such as ixodid ticks. Estonia is one of few regions where the distribution area of two medically important tick species, Ixodes persulcatus and I. ricinus, overlaps. The nidicolous rodent-associated Ixodes trianguliceps has also recently been shown to be present in Estonia. Although no data are available on human disease(s) caused by tick-borne Rickettsia spp. in Estonia, the presence of three Rickettsia species in non-nidicolous ticks has been previously reported. The aim of this study was to detect, identify and partially characterize Rickettsia species in nidicolous and non-nidicolous ticks attached to rodents in Estonia.

RESULTS

Larvae and nymphs of I. ricinus (n = 1004), I. persulcatus (n = 75) and I. trianguliceps (n = 117), all removed from rodents and shrews caught in different parts of Estonia, were studied for the presence of Rickettsia spp. by nested PCR. Ticks were collected from 314 small animals of five species [Myodes glareolus (bank voles), Apodemus flavicollis (yellow necked mice), A. agrarius (striped field mice), Microtus subterranius (pine voles) and Sorex araneus (common shrews)]. Rickettsial DNA was detected in 8.7% (103/1186) of the studied ticks. In addition to identifying R. helvetica, which had been previously found in questing ticks, we report here the first time that the recently described I. trianguliceps-associated Candidatus Rickettsia uralica has been identified west of the Ural Mountains.

Questing by Tick Larvae (Acari: Ixodidae): A Review of the Influences That Affect Off-Host Survival

Questing is a host-seeking behavior in which ticks ascend plants, extend their front legs, and wait poised for a chance to attach to a passing host. Hard ticks are ectoparasites of terrestrial vertebrates and because some species vector disease, they are among the most medically important of arthropod pests. All ixodid ticks require blood to survive and reproduce with the number of blood-hosts needed to complete their life cycle varying among species. The vast majority are three-host ticks requiring a different host for each developmental stage: larva, nymph, and adult. A few, including some of the most economically important species, are one-host ticks, that quest only in the larval stage. Questing is a rate-limiting behavior critical to tick survival and disease transmission. For the off-host larval stage, survival is highly dependent on ecological and physiological factors. Yet, off-host larval ecophysiology is often overlooked for the more obvious adult and nymphal tick-host interactions. This review summarizes the literature on ixodid larval questing with emphasis on how specific biotic and abiotic factors affect off-host survival.

Plant-Derived Natural Compounds for Tick Pest Control in Livestock and Wildlife: Pragmatism or Utopia?

Ticks and tick-borne diseases are a significant economic hindrance for livestock production and a menace to public health. The expansion of tick populations into new areas, the occurrence of acaricide resistance to synthetic chemical treatments, the potentially toxic contamination of food supplies, and the difficulty of applying chemical control in wild-animal populations have created greater interest in developing new tick control alternatives. Plant compounds represent a promising avenue for the discovery of such alternatives. Several plant extracts and secondary metabolites have repellent and acaricidal effects. However, very little is known about their mode of action, and their commercialization is faced with multiple hurdles, from the determination of an adequate formulation to field validation and public availability. Further, the applicability of these compounds to control ticks in wild-animal populations is restrained by inadequate delivery systems that cannot guarantee accurate dosage delivery at the right time to the target animal populations. More work, financial support, and collaboration with regulatory authorities, research groups, and private companies are needed to overcome these obstacles. Here, we review the advancements on known plant-derived natural compounds with acaricidal potential and discuss the road ahead toward the implementation of organic control in managing ticks and tick-borne diseases.

Recent research milestones in the pathogenesis of human rickettsioses and opportunities ahead

Infections caused by pathogenic Rickettsia species continue to scourge human health across the globe. From the point of entry at the site of transmission by arthropod vectors, hematogenous dissemination of rickettsiae occurs to diverse host tissues leading to 'rickettsial vasculitis' as the salient feature of pathogenesis. This perspective article accentuates recent breakthrough developments in the context of host-pathogen-vector interactions during rickettsial infections. The subtopics include potential exploitation of circulating macrophages for spread, identification of new entry mechanisms and regulators of actin-based motility, appreciation of metabolites acquired from and effectors delivered into the host, importance of the toxin-antitoxin module in host-cell interactions, effects of the vector microbiome on rickettsial transmission, and niche-specific riboregulation and adaptation. Further research on these aspects will advance our understanding of the biology of rickettsiae as intracellular pathogens and should enable design and development of new approaches to counter rickettsioses in humans and other hosts.

An exploratory analysis of demography and movement patterns of dogs: New insights in the ecology of endemic Rocky Mountain-Spotted Fever in Mexicali, Mexico

An outbreak of Rocky Mountain spotted fever (RMSF) transmitted by the brown dog tick (Rhipicephalus sanguineus sensu lato) has emerged as a major human and animal health concern in Mexicali, Mexico. Due to high rates of brown dog tick infestation, susceptibility, and association with humans, dogs serve as sentinels and have a key role in the ecology of RMSF. A cross-sectional household questionnaire study was conducted in six rural and urban locations to characterize dog ecology and demography in RMSF high-and low-risk areas of Mexicali. In addition, we tracked movement patterns of 16 dogs using a GPS data logger. Of 253 households, 73% owned dogs, and dog ownership tended to be higher in high-risk areas, with a mean dog:human ratio of 0.43, compared with 0.3 in low-risk areas. Dogs in high-risk areas had higher fecundity and roamed more, but the dog density and numbers of free-roaming dogs were comparable. There was a higher proportion of younger dogs and lower proportion of older dogs in high-risk areas. The high proportion of immunologically naïve puppies in high risk areas could result in a lack of herd immunity leading to a more vulnerable dog and human population. The marked increase of space use of free-roaming dogs in high-risk areas suggests that unrestrained dogs could play an important role in spreading ticks and pathogens. As means to limit RMSF risk, practical changes could include increased efforts for spay-neuter and policies encouraging dog restraint to limit canine roaming and spread of ticks across communities; due to dog density is less impactful such policies may be more useful than restrictions on the number of owned dogs.

Disease Ecology of Rickettsial Species: A Data Science Approach

We present an approach to assess the disease ecology of rickettsial species by investigating open databases and by using data science methodologies. First, we explored the epidemiological trend and changes of human rickettsial disease epidemics over the years and compared this trend with knowledge on emerging rickettsial diseases given by published reviews. Second, we investigated the global diversity of rickettsial species recorded in humans, domestic animals and wild mammals, using the Enhanced Infectious Disease Database (EID2) and employing a network analysis approach to represent and quantify transmission ecology of rickettsial species among their carriers, arthropod vectors or mammal reservoirs and humans. Our results confirmed previous studies that emphasized the increasing incidence in rickettsial diseases at the onset of 1970. Using the Global Infectious Diseases and Epidemiology Online Network (GIDEON) database, it was even possible to date the start of this increase of global outbreaks in rickettsial diseases in 1971. Network analysis showed the importance of domestic animals and peridomestic mammals in sharing rickettsial diseases with humans and other wild animals, acting as important hubs or connectors for rickettsial transmission.

Rickettsia and Anaplasma species in Dermacentor andersoni ticks from Washington

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

Molecular Detection of Rickettsia Spp. and Coxiella Burnetii in Cattle, Water Buffalo, and Rhipicephalus (Boophilus) Microplus Ticks in Luzon Island of the Philippines

Rickettsia and Coxiella burnetii are zoonotic, tick-borne pathogens that can cause febrile illnesses with or without other symptoms in humans, but may cause subclinical infections in animals. There are only a few reports on the occurrence of these pathogens in cattle and water buffalo in Southeast Asia, including the Philippines. In this study, molecular detection of Rickettsia and C. burnetii in the blood and in the Rhipicephalus (Boophilus) microplus ticks of cattle and water buffalo from five provinces in Luzon Island of the Philippines was done. A total of 620 blood samples of cattle and water buffalo and 206 tick samples were collected and subjected to DNA extraction. After successful amplification of control genes, nested PCR was performed to detect gltA of Rickettsia and com1 of C. burnetii. No samples were positive for Rickettsia, while 10 (cattle = 7, water buffaloes = 3), or 1.6% of blood, and five, or 1.8% of tick samples, were C. burnetii-positive. Sequence analysis of the positive amplicons showed 99-100% similarity to reported C. burnetii isolates. This molecular evidence on the occurrence of C. burnetii in Philippine ruminants and cattle ticks and its zoonotic nature should prompt further investigation and surveillance to facilitate its effective control.

Bacterial microbiota composition of Ixodes ricinus ticks: the role of environmental variation, tick characteristics and microbial interactions

Ecological factors, host characteristics and/or interactions among microbes may all shape the occurrence of microbes and the structure of microbial communities within organisms. In the past, disentangling these factors and determining their relative importance in shaping within-host microbiota communities has been hampered by analytical limitations to account for (dis)similar environmental preferences ('environmental filtering'). Here we used a joint species distribution modelling (JSDM) approach to characterize the bacterial microbiota of one of the most important disease vectors in Europe, the sheep tick Ixodes ricinus, along ecological gradients in the Swiss Alps. Although our study captured extensive environmental variation along elevational clines, the explanatory power of such large-scale ecological factors was comparably weak, suggesting that tick-specific traits and behaviours, microhabitat and -climate experienced by ticks, and interactions among microbes play an important role in shaping tick microbial communities. Indeed, when accounting for shared environmental preferences, evidence for significant patterns of positive or negative co-occurrence among microbes was found, which is indicative of competition or facilitation processes. Signals of facilitation were observed primarily among human pathogens, leading to co-infection within ticks, whereas signals of competition were observed between the tick endosymbiont Spiroplasma and human pathogens. These findings highlight the important role of small-scale ecological variation and microbe-microbe interactions in shaping tick microbial communities and the dynamics of tick-borne disease.

Epidemiology and Diversity of Rickettsiales Bacteria in Humans and Animals in Jiangsu and Jiangxi provinces, China

Diseases caused by Rickettsiales bacteria are a global public health problem. To better understand the diversity and origins of Rickettsiales infection in humans and animals, we sampled 134 febrile patients, 173 rodents and 43 shrews, as well as 358 ticks, from two cities in Jiangsu and Jiangxi provinces, China. Our data revealed a relatively high prevalence of scrub typhus cases in both localities. In addition, both serological tests and genetic analysis identified three patients infected with Anaplasma bovis, Rickettsia monacensis, and Orientia tsutsugamushi bacteria. Molecular epidemiological investigation revealed the co-circulation of multiple species of Rickettsiales bacteria in small mammals and ticks in both provinces, potentially including novel bacterial species. In sum, these data demonstrate the ongoing importance of Rickettsiales infection in China and highlight the need for the regular surveillance of local arthropods, mammals and humans.

When to Think of Rickettsia

Rickettsiae are globally encountered pathogens with foci of endemicity and epidemic exacerbations under circumstances of crowding and decline of sanitation. Diagnosis is often missed due to misconceptions about epidemiology, confusing terminology and nonspecific clinical presentation. Rickettsioses should be considered in children with febrile illnesses exceeding the usual duration of a viral infection, in particular in children with rash, lymphadenopathy and nearly normal first-line laboratory tests, who reside in or return from endemic areas, recall a compatible contact history, have a constellation of symptoms starting after an arthropod bite, live under troubled social circumstances, or are part of a cluster of similar cases.

Counterattacking the tick bite: towards a rational design of anti-tick vaccines targeting pathogen transmission

Hematophagous arthropods are responsible for the transmission of a variety of pathogens that cause disease in humans and animals. Ticks of the Ixodes ricinus complex are vectors for some of the most frequently occurring human tick-borne diseases, particularly Lyme borreliosis and tick-borne encephalitis virus (TBEV). The search for vaccines against these diseases is ongoing. Efforts during the last few decades have primarily focused on understanding the biology of the transmitted viruses, bacteria and protozoans, with the goal of identifying targets for intervention. Successful vaccines have been developed against TBEV and Lyme borreliosis, although the latter is no longer available for humans. More recently, the focus of intervention has shifted back to where it was initially being studied which is the vector. State of the art technologies are being used for the identification of potential vaccine candidates for anti-tick vaccines that could be used either in humans or animals. The study of the interrelationship between ticks and the pathogens they transmit, including mechanisms of acquisition, persistence and transmission have come to the fore, as this knowledge may lead to the identification of critical elements of the pathogens' life-cycle that could be targeted by vaccines. Here, we review the status of our current knowledge on the triangular relationships between ticks, the pathogens they carry and the mammalian hosts, as well as methods that are being used to identify anti-tick vaccine candidates that can prevent the transmission of tick-borne pathogens.

The growing importance of lone star ticks in a Lyme disease endemic county: Passive tick surveillance in Monmouth County, NJ, 2006 - 2016

As human cases of tick-borne disease continue to increase, there is a heightened imperative to collect data on human-tick encounters to inform disease prevention. Passive tick surveillance programs that encourage members of the public to submit ticks they have encountered can provide a relatively low-cost means of collecting such data. We report the results of 11 years of tick submissions (2006–2016) collected in Monmouth County, New Jersey, an Atlantic coastal county long endemic for Lyme disease. A total of 8,608 ticks acquired in 22 U.S. states were submitted, 89.7% of which were acquired in Monmouth County, from 52 of the County’s 53 municipalities. Seasonal submission rates reflected known phenology of common human-biting ticks, but annual submissions of both Amblyomma americanum and Dermacentor variabilis increased significantly over time while numbers of Ixodes scapularis remained static. By 2016, A. americanum had expanded northward in the county and now accounted for nearly half (48.1%) of submissions, far outpacing encounters with I. scapularis (28.2% of submissions). Across all tick species and stages the greatest number of ticks were removed from children (ages 0–9, 40.8%) and older adults (ages 50+, 23.8%) and these age groups were also more likely to submit partially or fully engorged ticks, suggesting increased risk of tick-borne disease transmission to these vulnerable age groups. Significantly more people (43.2%) reported acquiring ticks at their place of residence than in a park or natural area (17.9%). This pattern was more pronounced for residents over 60 years of age (72.7% acquired at home). Education that stresses frequent tick checks should target older age groups engaged in activity around the home. Our results strongly suggest that encounter rates with ticks other than I. scapularis are substantial and increasing and that their role in causing human illness should be carefully investigated.

Human-pathogenic Anaplasma spp., and Rickettsia spp. in animals in Xi'an, China

In China, thirteen species of tick-borne rickettsiales bacteria pathogenic to human have been reported in ticks and host animals, and human patients caused by them also has been identified. However, investigation for rickettsiales bacteria circulating in Xi'an wasn't performed although diseases resembling human diseases caused by these organisms have been found. In this study, domestic animals and ticks in Xi'an, China, were tested for the presence of rickettsiales bacteria pathogenic to humans. Besides A. ovis, a high prevalence of A. capra was observed suggesting a high public health risk exists. In addition, two novel Anaplasma species closely related to A. phagocytophilum were identified and formed distinct lineages in the phylogenetic trees, with more than 98.3% identities for rrs gene, while divergences up to 20.2% and 37.0% for groEL and gltA genes, respectively. Both of these two novel Anaplasma species were found to circulate in goats and further assessment of their pathogenicity is needed. Ca. R. jingxinensis, with potential pathogenicity, was also detected in H. longicomis ticks with high prevalence. However, other causative agents were not identified although they were distributed in other areas of China.

A review of the genus Rickettsia in Central America

In this paper, we present a historical review of rickettsiosis in Central America and also the most recent findings of Rickettsia in ectoparasites. All countries of Central America have records of rickettsiosis. Regarding the typhus group rickettsioses, there is clinical or serological evidence of Rickettsia prowazekii in Guatemala, Rickettsia typhi in Panama, Guatemala, and Costa Rica and unidentified species of the typhus group in El Salvador. Concerning spotted fever group rickettsiosis, there is serological evidence of infection by Rickettsia akari in Costa Rica and confirmed cases involving Rickettsia rickettsii in Panama and Costa Rica. There are also reports of spotted fever group rickettsiosis in acute patients from Guatemala, Honduras, and Nicaragua. Serological studies in Central America show reactivity of Rickettsia ambyommatis, Rickettsia bellii, Rickettsia felis, Rickettsia rhipicephali, and R. rickettsii in domestic and wild mammals. Eight species of Rickettsia have been detected in ectoparasites from Central America: R. africae (or very similar), R. amblyommatis, R. asembonensis, R. bellii, R. felis, R. parkeri, R. rhipicephali, and R. rickettsii, in addition to undescribed strains such as Atlantic Rainforest, Colombianensi, IbR/CRC, Barva, Aragaoi, and Candidatus "Rickettsia nicoyana;" the latter being the only one associated with Argasidae (Ornithodoros knoxjonesi). R. amblyommatis is the most common species in Central America, seeing as it has been reported in 10 species of ticks and one of fleas in five of the seven countries of the region. In this study, we demonstrate that the genus Rickettsia is widely distributed in Central America and that rickettsiosis could be an underestimated problem in the absence of greater diagnostic efforts in undetermined febrile cases.

Prevalence and diversity of Rickettsia species in ectoparasites collected from small rodents in Lithuania

BACKGROUND

Rickettsiae are emerging pathogens causing public health problems in many countries around the world. Rickettsia spp. are found in association with a wide range of arthropods which feed on different species of animals. However, the distribution and natural cycle of Rickettsia species and their association with different arthropod vectors are not fully established. The aim of this study was to investigate the presence and prevalence of Rickettsia spp. in ticks, mites and fleas parasitizing different species of small mammals in Lithuania and to molecularly characterize the Rickettsia spp. obtained from different ectoparasites.

RESULTS

A total of 1261 ectoparasites (596 Ixodes ricinus ticks, 550 mites of five species and 115 fleas of eight species) collected from 238 rodents in Lithuania during 2013-2014 were investigated for the presence of Rickettsia pathogens. Infection rates were calculated as the maximum likelihood estimation (MLE) with 95% confidence intervals (CI). The infection rate varied among ectoparasites and was found highest in fleas 43.5%, followed by I. ricinus ticks (MLE = 26.5%; 95% CI: 22.2-31.3%) and then mites (MLE = 9.3%; 95% CI: 7.0-12.2%). Sequence analysis of partial gltA and 17kDa genes revealed the presence of Rickettsia helvetica, R. felis, R. monacensis, Rickettsia sp. and rickettsial endosymbionts. Four Rickettsia spp. were identified in fleas, while three Rickettsia spp. were identified in Laelapidae mites and only one (R. helvetica) in I. ricinus ticks.

CONCLUSIONS

To our knowledge, this is the first report of the occurrence and molecular characterization of Rickettsia spp. in 11 species of ectoparasites of small rodents in Lithuania. The present data extend the knowledge on the distribution of Rickettsia spp. and their association with different arthropod vectors. Prior to our study, R. felis had never been identified in Lithuania. To our knowledge, this is also the first report of R. felis in L. agilis and H. microti mites and in Ct. agyrtes and H. talpae fleas, as well as the first detection of R. monacensis in Ct. agyrtes fleas.

Rickettsia helvetica in Human-Parasitizing and Free-Living Ixodes ricinus from Urban and Wild Green Areas in the Metropolitan City of Rome, Italy

Rickettsia helvetica is an emerging human pathogen, belonging to the spotted fever group (SFG) rickettsiae, associated with generally aneruptive fever, meningitis, and sudden death in chronic perimyocarditis. In this study, we describe the detection of R. helvetica in human-parasitizing and free-living Ixodes ricinus from the Metropolitan City of Rome. The pathogen was found in a tick acquired by a woman in an urban park. The circulation of R. helvetica was further confirmed by its detection in free-living ticks from a wild green area. These findings demonstrate that urban as well as wild green areas can represent a risk of infection to humans by R. helvetica, with potentially severe sequelae. To the best of our knowledge, this is the first report of R. helvetica in the Lazio region. Large-scale studies are needed to evaluate and quantify the presence of R. helvetica and other SFG rickettsiae in the urban and periurban context and to assess the risk to humans and animals related to their frequentation.