Candidatus Rickettsia tarasevichiae Infection in Eastern Central China: A Case Series

Demographic and zoological drivers of infectome diversity in companion cats with ascites

Cats (Felidae) have become an integral part of many households. However, our understanding of the full spectrum of pathogens affecting cats (referred to as the infectome) is limited, mainly due to the inadequacy of commonly used diagnostic tools in capturing the complete diversity of potential pathogens and the prevalence of pathogen co-infections. In this study, we employed a meta-transcriptomic approach to simultaneously characterize the infectome contributing to different disease syndromes and to investigate spatial, demographic, and ecological factors influencing pathogen diversity and community composition in a cohort of 27 hospitalized cats and seven stray cats. We identified 15 species of pathogens, with Candidatus Rickettsia tarasevichiae and Tritrichomonas foetus representing potential spillover risks. Importantly, although most cases of ascites hyperplasia were explained by coinfection with multiple pathogens, we identified the potential novel clinical outcomes of M. aubagnense infection among cats. We demonstrated that the increase in infectome diversity can be explained by a variety of predictors including age growth, temperature increase, and a higher proportion of females, with age growth presenting the strongest effect. Fine-scale analysis indicated that a higher diversity of infectomes were harbored in young cats rather than adult ones. Our results demonstrated that most feline diseases are better explained by the presence of virus-bacteria or virus-virus coinfection. This study serves as a timely endorsement for clinical diagnosis by vets to consider the cause of a disease based on a panel of cryptical co-infecting pathogens rather than on individual infectious agents.

IMPORTANCE

Frequent studies reported the risks of cats as an intermediate host of zoonotic pathogens (e.g., SARS-CoV-2). Cats have a physically close interaction with their owners through activities like petting, kissing, and being licked on the cheek and hands. However, there are still limited studies that systematically investigate the infectome structure of cats. In this study, we employed a meta-transcriptomics approach to characterize 15 species of pathogens in cats, with Candidatus Rickettsia tarasevichiae first characterizing infection in diseased cats. Most feline diseases were better explained by the presence of virus-bacteria or virus-virus coinfection. The increase in infectome diversity could be influenced by a variety of predictors including age growth, temperature increase, and a higher proportion of females. A higher diversity of pathogens was harbored in young cats rather than adults. Importantly, we showed the value of linking the modern influx of meta-transcriptomics with comparative ecology and demography and of utilizing it to affirm that ecological and demographic variations impact the total infectome.

Stomach as the target organ of Rickettsia heilongjiangensis infection in C57BL/6 mice identified by click chemistry

Spotted fever group rickettsiae (SFGR) are obligate intracellular bacteria that cause spotted fever. The limitations of gene manipulation pose great challenges to studying the infection mechanisms of Rickettsia. By combining bioorthogonal metabolism and click chemistry, we developed a method to label R. heilongjiangensis via azide moieties and achieved rapid pathogen localization without complex procedures. Moreover, we constructed a C57BL/6 mice infection model by simulating tick bites and discovered that the stomach is the target organ of R. heilongjiangensis infection through in vivo imaging systems, which explained the occurrence of gastrointestinal symptoms following R. heilongjiangensis infection in some cases. This study offers a unique perspective for subsequent investigations into the pathogenic mechanisms of SFGR and identifies a potential target organ for R. heilongjiangensis.

First detection of Candidatus Rickettsia tarasevichiae in Hyalomma marginatum ticks

Ticks are important vectors of zoonotic diseases and play a major role in the circulation and transmission of many rickettsial species. The aim of this study was to investigate the carriage of Candidatus Rickettsia tarasevichiae (CRT) in a total of 1168 ticks collected in Inner Mongolia to elucidate the potential public health risk of this pathogen, provide a basis for infectious disease prevention, control and prediction and contribute diagnostic ideas for clinical diseases that present with fever in populations exposed to ticks. A total of four tick species, Haemaphysalis concinna (n = 21), Dermacentor nuttalli (n = 122), Hyalomma marginatum (n = 148), and Ixodes persulcatus (n = 877), were collected at nine sampling sites in Inner Mongolia, China, and identified by morphological and molecular biological methods. Reverse transcription PCR targeting the 16S ribosomal RNA (rrs), gltA, groEL, ompB and Sca4 genes was used to detect CRT DNA. Sequencing was used for pathogen species confirmation. The molecular epidemiological analysis showed that three species of ticks were infected with CRT, and the overall positive rate was as high as 42%. The positive rate of I. persulcatus collected in Hinggan League city was up to 96%, and that of I. persulcatus collected in Hulun Buir city was 50%. The pool positive rates of D. nuttalli and H. marginatum collected in Bayan Nur city and H. concinna collected in Hulun Buir city were 0%, 28% and 40%, respectively. This study revealed the high prevalence of CRT infection in ticks from Inner Mongolia and the first confirmation of CRT detected in H. marginatum in China. The wide host range and high infection rate in Inner Mongolia may dramatically increase the exposure of CRT to humans and other vertebrates. The role of H. marginatum in the transmission of rickettsiosis and its potential risk to public health should be further considered.

The presence of foci of Rickettsia conorii infection in China

China is not considered as an endemic area of Rickettsia conorii, so there is no routine clinical way to diagnose this infection. This study aims to determine whether 2 febrile patients who had a tick bite in East China were indeed infected with R. conorii. The citrate synthase gene (gltA) was amplified with universal rickettsial primers by real-time fluorescent PCR from the patients' blood samples. Nested PCR was used to amplify the outer membrane protein A gene (ompA) for positive specimens. PCR products were further identified and analyzed through nucleic acid sequencing. Positive amplification of the gltA and ompA genes was found in both patients. The nucleotide sequences (303 bp) of the ompA gene of the 2 patients had high homology (99%) with the R. conorii Indian tick typhus strain in GenBank. A more than 4-fold increase in IgG against R. conorii provided supportive evidence of SFG Rickettsia infection. And the rapid recovery after doxycycline treatment also supported a rickettsial cause for the disease. Physicians in East China should be aware of human infections with R. conorii. PCR-based diagnostic methods offer a rapid and precise way to diagnose rickettsiosis, improving patient identification and management.

Molecular surveillance reveals a potential hotspot of tick-borne disease in Yakeshi City, Inner Mongolia

A molecular surveillance of tick-borne diseases was performed in Hulunbuir City, Inner Mongolia. A total of 149 ticks including three species (Ixodes persulcatus, Haemaphysalis concinna, and Dermacentor silvarum) were collected. As many as 11 tick-borne bacterial pathogens were identified in them. Some of them have high positive rates. For example, Candidatus Rickettsia tarasevichiae was detected with a high prevalence of 72.48%, while Candidatus Lariskella sp. was detected in 31.54% of ticks. For both Rickettsia raoultii and Anaplasma phagocytophilum, two distinct genotypes were identified based on their phylogenetic trees based on 16S rRNA, gltA, and groEL sequences. Remarkable genetic diversity was also observed for 16S and flaB genes of Borreliella garinii, an agent of Lyme disease. Rickettsia heilongjiangensis causing Far-Eastern spotted fever (2.68%, 4/149), Ehrlichia muris causing human ehrlichiosis (4.70%, 7/149), Borrelia miyamotoi causing relapsing fever (2.01%, 3/149), and Borreliella afzelii causing Lyme disease (2.01%, 3/149) were also detected. Additionally, a previously uncharacterized Anaplasma species closely related to Anaplasma ovis was identified. Herein we name it "Candidatus Anaplasma mongolica". Based on these results, we propose that Yakeshi City might be a potential hotspot of tick-borne diseases.

Molecular and seroepidemiological investigation of Сoxiella burnetii and spotted fever group rickettsiae in the southern region of Kazakhstan

Ticks are involved in the circulation of a number of human pathogens, including spotted fever group (SFG) Rickettsia spp. and Coxiella burnetii. Little is known about the occurrence of these microorganisms in the southern region of Kazakhstan. In 2018-2022, a total of 726 ticks were collected from bitten humans, livestock, and vegetation in four oblasts of the southern region of Kazakhstan and subjected to DNA extraction. The overall infection rate of Coxiella spp. and Rickettsia spp. in the ticks was 3.3% (24/726) and 69.9% (300/429), respectively. Phylogenetic analysis of ompA and gltA genes revealed the presence of three pathogenic SFG rickettsiae: Candidatus R. tarasevichiae, R. aeschlimannii and R. raoultii in ticks collected from bitten humans. In addition, Candidatus R. barbariae was detected in six Rhipicephalus turanicus ticks for the first time in Kazakhstan. To determine the seroprevalence of C. burnetii infection, we performed a serological analysis of samples collected from 656 domestic ruminants (cattle, sheep, and goats) in the region. Overall, 23.5% (154/656) of the animals tested were positive for IgG against C. burnetii. Seroprevalence at the herd level was 54% (28/52). Goats (43%; 12/28; odds ratio (OD) = 28.9, p < 0.05) and sheep (31.9%; 137/430; OD = 18.1, p < 0.05) had higher seroprevalence than cattle (2.5%; 5/198). Among the risk factors considered in this study, age (p = 0.003) and the oblast in which the animals were sampled (p = 0.049) were statistically associated with seropostivity for Q fever in sheep, according to the results of multivariate logistic regression analysis. Seroprevalence ranged from 0% to 55.5% in animals in different districts of the southern region of Kazakhstan. Active C. burnetii bacteremia was detected in four of 154 (2.6%) seropositive animals. The data obtained provide strong evidence of the presence of pathogenic rickettsiae and C. burnetii in the southern region of Kazakhstan and emphasize the need to improve epidemiological surveillance in the region.

Molecular Detection of Tick-Borne Bacterial and Protozoan Pathogens in Haemaphysalis longicornis (Acari: Ixodidae) Ticks from Free-Ranging Domestic Sheep in Hebei Province, China

Ticks and tick-borne pathogens significantly threaten human and animal health worldwide. Haemaphysalis longicornis is one of the dominant tick species in East Asia, including China. In the present study, 646 Ha. longicornis ticks were collected from free-ranging domestic sheep in the southern region of Hebei Province, China. Tick-borne pathogens of zoonotic and veterinary importance (i.e., Rickettsia, Anaplasma, Ehrlichia, Borrelia, Theileria, and Hepatozoon spp.) were detected in the ticks using PCR assays and sequence analysis. The prevalence rates of these pathogens were 5.1% (33/646), 15.9% (103/646), 1.2% (8/646), 17.0% (110/646), 0.15% (1/646), and 0.15% (1/646), respectively. For Rickettsia spp., R. japonica (n = 13), R. raoultii (n = 6), and Candidatus R. jingxinensis (n = 14) were detected for the first time in the province, while several Anaplasma spp. were also detected in the ticks, including A. bovis (n = 52), A. ovis (n = 31), A. phagocytophilum (n = 10), and A. capra (n = 10). A putative novel Ehrlichia spp. was also found with a prevalence of 1.2% in the area. The present study provides important data for effectively controlling ticks and tick-borne diseases in the Hebei Province region of China.

Novel Genetic Lineages of Rickettsia helvetica Associated with Ixodes apronophorus and Ixodes trianguliceps Ticks

Ixodes apronophorus is an insufficiently studied nidicolous tick species. For the first time, the prevalence and genetic diversity of Rickettsia spp. in Ixodes apronophorus, Ixodes persulcatus, and Ixodes trianguliceps ticks from their sympatric habitats in Western Siberia were investigated. Rickettsia helvetica was first identified in I. apronophorus with a prevalence exceeding 60%. "Candidatus Rickettsia tarasevichiae" dominated in I. persulcatus, whereas I. trianguliceps were infected with "Candidatus Rickettsia uralica", R. helvetica, and "Ca. R. tarasevichiae". For larvae collected from small mammals, a strong association was observed between tick species and rickettsiae species/sequence variants, indicating that co-feeding transmission in studied habitats is absent or its impact is insignificant. Phylogenetic analysis of all available R. helvetica sequences demonstrated the presence of four distinct genetic lineages. Most sequences from I. apronophorus belong to the unique lineage III, and single sequences cluster into the lineage I alongside sequences from European I. ricinus and Siberian I. persulcatus. Rickettsia helvetica sequences from I. trianguliceps, along with sequences from I. persulcatus from northwestern Russia, form lineage II. Other known R. helvetica sequences from I. persulcatus from the Far East group into the lineage IV. The obtained results demonstrated the high genetic variability of R. helvetica.

Co-infection of tick-borne bacterial pathogens in ticks in Inner Mongolia, China

Tick-borne infectious diseases pose a serious health threat in certain regions of the world. Emerging infectious diseases caused by novel tick-borne pathogens have been reported that are causing particular concern. Several tick-borne diseases often coexist in the same foci, and a single vector tick can transmit two or more pathogens at the same time, which greatly increases the probability of co-infection in host animals and humans and can lead to an epidemic of tick-borne disease. The lack of epidemiological data and information on the specific clinical symptoms related to co-infection with tick-borne pathogens means that it is not currently possible to accurately and rapidly distinguish between a single pathogen infection and co-infection with multiple pathogens, which can have serious consequences. Inner Mongolia in the north of China is endemic for tick-borne infectious diseases, especially in the eastern forest region. Previous studies have found that more than 10% of co-infections were in host-seeking ticks. However, the lack of data on the specific types of co-infection with pathogens makes clinical treatment difficult. In our study, we present data on the co-infection types and the differences in co-infection among different ecological regions through genetic analysis of tick samples collected throughout Inner Mongolia. Our findings may aid clinicians in the diagnosis of concomitant tick-borne infectious diseases.

Pathogens in Ixodes persulcatus and Ixodes ricinus ticks (Acari, Ixodidae) in Karelia (Russia)

Ixodid ticks (Acarina, Ixodidae) are vectors of dangerous human infections. The main tick species that determine the epidemiological situation for tick-borne diseases in northern Europe are Ixodes ricinus and Ixodes persulcatus. In recent years, significant changes in the number and distribution of these species have been observed, accompanied by an expansion of the sympatric range. This work summarizes the data of long-term studies carried out in Karelia since 2007 on the infection of I. persulcatus and I. ricinus ticks with various pathogens, including new viruses with unclear pathogenic potential. As a result, tick-borne encephalitis virus (TBEV, Siberian genotype), Alongshan virus, several representatives of the family Phenuiviridae, Borrelia afzelii, Borrelia garinii, Ehrlichia muris, Candidatus Rickettsia tarasevichiae and Candidatus Lariskella arthropodarum were identified. Data were obtained on the geographical and temporal variability of tick infection rates with these main pathogens. The average infection rates of I. persulcatus with TBEV and Borrelia burgdorferi sensu lato were 4.4% and 23.4% and those of I. ricinus were 1.1% and 11.9%, respectively. We did not find a correlation between the infection rate of ticks with TBEV, B. burgdorferi s.l. and Ehrlichia muris/chaffeensis with the sex of the vector. In general, the peculiarities of the epidemiological situation in Karelia are determined by the wide distribution and high abundance of I. persulcatus ticks and by their relatively high infection rate with TBEV and B. burgdorferi s.l. in most of the territory, including the periphery of the range.

Survey of tick species and molecular detection of selected tick-borne pathogens in Yanbian, China

Ticks and tick-borne diseases pose a significant threat to public health. In this study, we aimed to determine the tick species distribution and pathogens carried by ticks in Yanbian, China. A total of 2673 questing ticks were collected from eight counties and cities in Yanbian and were morphologically identified. The presence of Candidatus Rickettsia tarasevichiae (CRT), spotted fever group Rickettsia (SFGR), severe fever thrombocytopenia syndrome virus (SFTSV), Theileria, and other pathogens was confirmed using polymerase chain reaction (PCR) and real-time quantitative PCR assays, followed by phylogenetic and genotypic analyses. According to the morphological identification, the tick species in Yanbian consisted of Haemaphysalis longicornis, Ixodes persulcatus, Dermacentor silvarum, H. japonica, and H. concinna. In H. longicornis, CRT, SFGR, SFTSV and Theileria orientalis were detected, while CRT, SFGR, and SFTSV were detected in I. persulcatus, H. japonica, and D. silvarum. Only SFTSV was detected in H. concinna. Mixed infection with CRT and SFTSV was observed in I. persulcatus and H. japonica. The gene sequences of all tested pathogens exhibited 95.7%–100% identity with the corresponding sequences deposited in GenBank. Phylogenetic analysis showed that different SFGR and SFTSV genotypes were closely related to the Korean strains. This study is the first to describe the genetic diversity of SFGR Candidatus Rickettsia longicornii in H. longicornis in Yanbian, China, using the ompA, ompB, sca4, and rrs genes. These results provide epidemiological data to support the prevention and control of ticks and tick-borne diseases in the border areas of China, North Korea, and Russia.

Molecular detection of Borrelia burgdorferi (sensu lato) and Rickettsia spp. in hard ticks distributed in Tokachi District, eastern Hokkaido, Japan

Ticks transmit various pathogens, including parasites, bacteria and viruses to humans and animals. To investigate the ticks and the potentially zoonotic pathogens that they may carry, questing ticks were collected in 2017 from 7 sites in Tokachi District, eastern Hokkaido, Japan. A total of 1563 ticks including adults (male and female), nymphs and larvae were collected. Four species of ticks were identified: Ixodes ovatus, Ixodes persulcatus, Haemaphysalis japonica and Haemaphysalis megaspinosa. Of the 1563 ticks, 1155 were used for DNA extraction. In total, 527 individual tick DNA samples prepared from adults (n = 484), nymphs (n = 41) and larvae (n = 2); and 67 pooled tick DNA samples prepared from larval stages (n = 628) were examined using PCR methods and sequencing to detect Borrelia burgdorferi (sensu lato) and Rickettsia spp. The phylogenetic analysis of Borrelia spp. flaB gene sequences showed the presence of the human pathogenic B. burgdorferi (s.l.) species (Borrelia garinii, Borrelia bavariensis and Borrelia afzelii) in I. persulcatus, whereas the non-pathogenic species Borrelia japonica was found only in I. ovatus. In I. persulcatus, B. garinii and/or its closely related species B. bavariensis was detected in both adults and nymphs at a prevalence of 21.9% whereas B. afzelii was found only in adults (1.8%). The prevalence of B. japonica in adult I. ovatus was 21.8%. Rickettsia species were identified through phylogenetic analysis based on gltA, 16S rRNA, ompB and sca4 genes. Four genotypes were detected in the samples which were classified into three species. The prevalence of human pathogenic Rickettsia helvetica was 26.0% in I. persulcatus adults and nymphs, 55.6% in I. persulcatus larval pools, and 1.7% in H. megaspinosa larval pools. The prevalence of “Candidatus R. tarasevichiae” was 15.4% in I. persulcatus adults and nymphs and 33.3% in I. persulcatus larval pools. The prevalence of “Candidatus R. principis” in H. megaspinosa adults and nymphs was 11.1% whereas it was detected in 3.4% of the H. megaspinosa larval pools. These results indicate that most of the risks of Lyme borreliosis and spotted fever group rickettsiosis infection in eastern Hokkaido, Japan, are restricted to I. persulcatus.

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Four species of ticks were collected in Tokachi District, eastern Hokkaido, Japan.

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Tick DNA samples were subjected to PCR to detect Borrelia spp. and Rickettsia spp.

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Borrelia garinii/Borrelia bavariensis and Borrelia afzelii were detected in Ixodes persulcatus.

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Rickettsia helvetica and “Candidatus R. tarasevichiae” were detected in I. persulcatus.

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First molecular detection of “Candidatus R. principis” in larvae of Haemaphysalis megaspinosa.

Mononucleosis-like illnesses due to co-infection with severe fever with thrombocytopenia syndrome virus and spotted fever group rickettsia:a case report

Background

We report a mononucleosis-like illnesses case due to co-infection with severe fever with thrombocytopenia syndrome virus (SFTSV) and spotted fever group rickettsia (SFGR), which to the best of our knowledge, has never been reported .

Case presentation

A 64-year-old male with an 11-day history of fever, sore throat, malaise, nausea, and non-pruritic rash was admitted to our emergency department. Prior to admission, he was bitten by ticks. Laboratory tests revealed a white blood cell count of 24,460 cells/μL with 25% atypical lymphocytes and 20% mononucleosis, thrombocytopenia. Test results were positive for SFTSV RNA, SFTSV-specific IgM antibody, and SFGR-specific IgM antibody. He was diagnosed with mononucleosis-like illnesses due to co-infection with SFTSV and SFGR. After administration of doxycycline, he recovered completely.

Conclusions

The clinical presentation may be atypical in co-infection with SFTSV and SFGR. This finding highlighted the importance of considering SFGR infection, as well as a SFSTV and SFGR co-infection for the differential diagnosis of patients bitten by ticks in SFTSV-endemic areas.

Candidatus Rickettsia xinyangensis as Cause of Spotted Fever Group Rickettsiosis, Xinyang, China, 2015

In 2015, we evaluated 221 patients with undifferentiated fever and tick bite or animal exposure in Xinyang, China, for Rickettsia infection. Three with mild disease were infected with Candidatus R. xinyangensis, which clustered with R. fournieri and R. vini in phylogenetic analyses. Field investigations suggest Haemaphysalis longicornis ticks might be involved in transmission.

Molecular detection and genetic diversity of Rickettsia spp. in pet dogs and their infesting ticks in Harbin, northeastern China

Background

Pet dogs are important companion animals that share the environment within households, and play an important role in local community life. In addition, pet dogs also are reservoirs of zoonotic agents, including Rickettsia spp., thus increasing the risk of rickettsial infections in humans. It’s meaningful to investigate the epidemiology of rickettsial agents in pet dogs, and make contribute to the surveillance of rickettsioses in human in China.

Results

In this study, a total of 496 pet dogs’ blood samples and 343 ticks infested in pet dogs were collected, and the presence and prevalence of Rickettsia were determined by amplifying the partial gltA and 17-kDa genes, with an overall positive rate of 8.1 % in blood samples and 14.0 % in tick samples. In addition, the rrs, gltA, groEL, and ompA genes of rickettsial were also recovered to determine the species of Rickettsia detected furtherly. Sequencing blast and phylogenetic analyses revealed the presence of three human pathogenic Rickettsia species (Rickettsia raoultii, Candidatus Rickettsia tarasevichiae and Rickettsia felis) in samples associated with pet dogs. Moreover, all the sequences of Rickettsia that we obtained presented close relationship with others available in GenBank, and Rickettsia raoultii was the most predominant Rickettsia species infected in pet dogs’ blood samples or in tick samples.

Conclusions

This study provides the molecular epidemiology data about the Rickettsia spp. infection associated with pet dogs in urban areas of Harbin city. Three rickettisae species pathogenic to humans were identified from pet dogs’ blood and the infested ticks in urban areas of Harbin city. Considering the intimate relationship between human and pets, these results indicate the potential transmission risk of human rickettisal infections from pet dogs through ectoparasites, and also highlighting that more attention should be paid to rickettsial infection in pet dogs and the infested ticks from the “One health” perspective.

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.

Severe fever with thrombocytopenia syndrome virus: a highly lethal bunyavirus

Severe fever with thrombocytopenia syndrome virus (SFTSV) is a novel bunyavirus. Since 2007, SFTS disease has been reported in China with high fatality rate up to 30%, which drew high attention from Centre for Disease Control and Prevention and government. SFTSV is endemic in the centra l and eastern China, Korea and Japan. There also have been similar cases reported in Vietnam. The number of SFTSV infection cases has a steady growth in these years. As SFTSV could transmitted from person to person, it will expose the public to infectious risk. In 2018 annual review of the Blueprint list of priority diseases, World Health Organisation has listed SFTSV infection as prioritised diseases for research and development in emergency contexts. However, the pathogenesis of SFTSV remains largely unclear. Currently, there are no specific therapeutics or vaccines to combat infections of SFTSV. This review discusses recent findings of epidemiology, transmission pathway, pathogenesis and treatments of SFTS disease.

Distribution and molecular characterization of rickettsiae in ticks in Harbin area of Northeastern China

Tick-borne rickettsioses are world-spreading infectious zoonoses. Ticks serve as reservoirs and vectors for Rickettsia and play a key role in transmission of rickettsioses. Most of the Chinese rickettsiosis patients are reported from Northeastern China but the distribution of tick and tick-borne Rickettsia species in Northeastern China remain poorly studied. In this study, a total of 1,286 ticks were captured from the seven counties of Harbin, an area in Northeastern China, and the tick-borne Rickettsia species were identified by PCR and sequencing of rrs, gltA, groEL, ompA and 17-kDa antigen-encoding genes. Of the 5 identified tick species, Haemaphysalis longicornis and Ixodes persulcatus were the predominant tick species in the livestock and vegetation, respectively. Rickettsia raoultii and “Candidatus Rickettsia tarasevichiae” were the two detectable Rickettsia species in the ticks with a 28.8% positive rate but no rickettsiae were found in ticks of Haemaphysalis concinna. R. raoultii detected in 37.6% of the Dermacentor nuttalli, Dermacentor silvarum and H. longicornis ticks while “Ca. R. tarasevichiae” was only present in 22.8% of the I. persulcatus ticks. In particular, the positive rate of both R. raoultii and “Ca. R. tarasevichiae” in ticks from the livestock (40.7%) was significantly higher than that from the vegetation (19.5%). The results indicate that the tick and tick-borne Rickettsia species are diverse in different regions of Harbin due to geographic difference and the ticks from livestock may play a more important role in transmission of rickettsioses to human.

Rickettsiosis is a tick-borne infectious disease of global importance. The disease has been prevailing in Northeastern China but the distribution of tick and tick-borne Rickettsia species from different areas of Northeastern China remain poorly studied. We collected a total of 1,286 ticks in the seven counties with different geographic environments of Harbin, an area of Northeastern China, and all the ticks were classified as Dermacentor nuttalli, Dermacentor silvarum, Haemaphysalis concinna, Haemaphysalis longicornis or Ixodes persulcatus. A total of 28.8% of the ticks tested positive for either Rickettsia raoultii or “Candidatus Rickettsia tarasevichiae”, in which 37.6% of the D. nuttalli, D. silvarum and H. longicornis ticks were positive for R. raoultii while 22.8% of the I. persulcatus ticks were positive for “Ca. R. tarasevichiae”. The positive rate of both R. raoultii and “Ca. R. tarasevichiae” in ticks from the livestock (40.7%) was significantly higher than that from the vegetation (19.5%). All the data indicate that ticks in the Harbin area have a high infection rate with Rickettsia species and domestic animals may have a tick-livestock rickettsial circulation that may play an important role in transmission of rickettsioses.

Human Spotted Fever Group Rickettsia Infecting Yaks (Bos grunniens) in the Qinghai-Tibetan Plateau Area

The Qinghai-Tibetan Plateau Area (QTPA) is a plateau with the highest average altitude, located in Northwestern China. There is a risk for interspecies disease transmission, such as spotted fever rickettsioses. However, information on the molecular characteristics of the spotted fever group (SFG) Rickettsia spp. in the area is limited. This study performed screenings, and detected the DNA of human pathogen, SFG Rickettsia spp., with 11.3% (25/222) infection rates in yaks (Bosgrunniens). BLASTn analysis revealed that the Rickettsia sequences obtained shared 94.3–100% identity with isolates of Rickettsia spp. from ticks in China. One Rickettsia sequence (MN536161) had 100% nucleotide identity to two R. raoultii isolates from Chinese Homo sapiens, and one isolate from Qinghai Dermacentorsilvarum. Meanwhile, another Rickettsia sequence (MN536157) shared 99.1–99.5% identity to one isolate from Dermacentor spp. in China. Furthermore, the phylogenetic analysis of SFG Rickettsia spp. ompA gene revealed that these two sequences obtained from yaks in the present study grouped with the R. slovaca and R. raoultii clades with isolates identified from Dermacentor spp. and Homo sapiens. Our findings showed the first evidence of human pathogen DNA, SFG Rickettsia spp., from animals, in the QTPA.

First Confirmed Infection of Candidatus Rickettsia Tarasevichiae in Rodents Collected from Northeastern China

Background: To date, there have been few investigations on Candidatus Rickettsia tarasevichiae in rodents carried out in China. In this study, we conducted surveillance for Candidatus R. tarasevichiae infection in rodents. A total of 463 rodents were captured at five survey sites in Mudanjiang, Heilongjiang province, where Candidatus R. tarasevichiae patients have been reported. PCR targeting citrate synthase and outer membrane protein genes was performed and positive amplicons were sequenced. Result: Candidatus R. tarasevichiae was detected in 1.29% of the 463 rodents sampled from the five survey sites in Mudanjiang, Heilongjiang province. Only 2 out of 13 (15.38%) Rattus norvegicus and 4 out of 80 (5%) Clethrionomys rufocanus collected from Dashigou forestry were positive for the gltA and ompA genes of Candidatus R. tarasevichiae DNA. The detected Candidatus R. tarasevichiae was in the same clade of sequences from patients in Mudanjiang based on phylogenetic analysis. Conclusion: Rodents are major host of ticks and also serve as reservoirs of spotted fever group (SFG) Rickettsia. Although this is the first confirmation of Candidatus R. tarasevichiae detected in rodents in China, further investigations are needed to clarify the distribution of Candidatus R. tarasevichiae in rodents elsewhere and what role they play as reservoirs.

Emergence of human infection with Jingmen tick virus in China: A retrospective study

Background

A tick-borne segmented RNA virus called Jingmen tick virus (JMTV) was recently identified, variants of which were detected in a non-human primate host and fatal patients with Crimean-Congo haemorrhagic fever. We investigated its infectivity and pathogenicity for humans.

Methods

We obtained skin-biopsy, blood and serum samples from patients with tick bites, and used high-throughput sequencing, in situ hybridisation, and serologic testing to diagnose and ascertain the cases of JMTV infection.

Findings

A JMTV strain was isolated from the tick Amblyomma javanense into an embryo-derived tick cell line. We obtained sustained passage of JMTV, and revealed that it was able to accumulate in salivary glands of experimentally infected ticks. Four JMTV-infected patients were identified by high-throughput sequencing of skin biopsies and blood samples. The virus replication in skin tissue was visualised by in situ hybridisation. The four patients all had an itchy or painful eschar at the site of tick bite, with or without lymphadenopathy. Immunohistochemical examination revealed remarkable local inflammation manifested as infiltration by neutrophils. Eight patients were identified by serological testing and showed more severe clinical manifestations. Two Ixodes persulcatus ticks detached from patients were positive for JMTV. All JMTV strains identified in this study formed a well-supported sub-lineage, distinct from those previously reported in China.

Interpretation

The public significance of JMTV should be highly concerning due to its potential pathogenicity for humans and efficient transmission by potential ticks.

Fund

China Natural Science Foundation, State Key Research Development Programme, and United Kingdom Biotechnology and Biological Sciences Research Council.

Features of the Epidemiological Situation on Siberian Tick Typhus and other Tick-Borne Ricketsioses in the Russian Federation, Prognosis for 2019

The review presents an analysis of the epidemic situation on infections of rickettsial etiology, the causative agents of which are transmitted by Ixodidae ticks in the territory of the Russian Federation. The data obtained through molecular-biological verification allow to unite under the name of “tick-borne ricketsioses” a group of infections caused by R. sibirica subsp. sibirica, R. conorii, R. heilongjiangensis and other species of rickettsiae circulating in natural foci of various regions of Russia. Cases of tick-borne rickettsioses in Siberia and the Far East, caused by various species of rickettsiae, are registered under the name of “Siberian tick-borne typhus” due to the lack of available methods of differential laboratory diagnostics. The paper presents the assessment of the incidence of Siberian tick-borne typhus, indicating not only the varying degrees of epidemic hazard of endemic regions, but also changes in the distribution of risk areas, including the identification of new, epidemically significant foci. In accordance with the risk-oriented approach to prophylaxis, forecasting of epidemic situation on tick-borne rickettsioses was given and differentiation of the endemic territories of the Russian Federation as regards Siberian tick-borne typhus was carried out with distinguishing of epidemiological zones of low, medium, above average, high and very high risk of population infection.

Report of Non-Lyme, Erythema Migrans Rashes from New Jersey with a Review of Possible Role of Tick Salivary Toxins

Erythema migrans (EM) rashes once considered pathognomonic of Lyme disease (LD) have been reported following bites of arthropods that do not transmit LD and in areas with no LD. Also, EM rashes have been reported in association with organisms other than members of Borrelia burgdorferi sensu lato complex. Arthropod saliva has chemicals that have effects on the host and pathogen transmission. Tick saliva has protein families similar to spiders and scorpions and even substances homologous to those found in snakes and other venomous animals. Ticks "invertebrate pharmacologists" have a sophisticated arsenal of chemicals that assist in blood feeding, pathogen transmission, and suppressing host defenses. No organisms have been isolated from many EM rashes. We propose that tick salivary toxins may play a role in the causation of rashes and laboratory abnormalities in tick-borne diseases. The role of tick salivary toxins needs further exploration. Cases of Lyme-like EM rashes referred to as STARI (Southern Tick-Associated Rash Illness) following bites of the lone star tick, Amblyomma americanum, in the United States have been reported predominantly in Southeastern Missouri and a few in South Carolina, North Carolina, Georgia, and one case each in Mississippi and Long Island, New York. Although there is one report of Borrelia lonestari in a patient with a rash, biopsies of 31 cases of STARI, with cultures and PCR, failed to show a relationship. Distribution of A. americanum, whose bites are associated with STARI, now extends along the East Coast of the United States, including New Jersey, up to the Canadian border. As far as we are aware, there have been no prior reports of Lyme-like rashes in New Jersey. In this study, we present case examples of 2 Lyme-like rashes, variations of EM rashes, and a brief review of studies that suggest a role of tick salivary toxins in tick-borne diseases.

Genetic variability of Rickettsia spp. in Dermacentor and Haemaphysalis ticks from the Russian Far East

The Russian Far East is an endemic region for tick-borne rickettsioses. However, the prevalence and genetic variability of Rickettsia species in this region have not been extensively investigated. In this study, 188 Dermacentor silvarum, 439 Haemaphysalis concinna, and 374 Haemaphysalis japonica adult ticks were collected from four locations in Khabarovsk Province and three locations in Amur Province in the Russian Far East. These ticks were examined for the presence of Rickettsia spp. by amplifying a fragment of the gltA gene. Identified rickettsiae were genotyped by sequencing of the gltA, 16S rRNA, ompA, ompB, and sca4 genes. In the examined ticks, Rickettsia heilongjiangensis, the causative agent of Far-Eastern tick-borne rickettsiosis, was found in 10.5% of H. concinna and in 1.9% of H. japonica ticks, while Rickettsia sibirica, the agent of Siberian tick typhus, was detected in only one H. concinna tick. In addition, Rickettsia raoultii was found predominantly in D. silvarum (>70%) and significantly less frequently in Haemaphysalis ticks (<3%). "Candidatus Rickettsia tarasevichiae" was found in all examined tick species (1.6-5.3% in different species). Notably, this study is the first observation of "Candidatus R. tarasevichiae" in D. silvarum ticks. Moreover, DNA of Rickettsia canadensis was found for the first time in a H. japonica tick; DNA of Rickettsia aeschlimannii was revealed for the first time in H. concinna and H. japonica ticks. "Candidatus Rickettsia principis" and "Candidatus Rickettsia rara" were found in Haemaphysalis spp. ticks. "Candidatus R. principis" was associated with H. japonica and identified in 5.6% of the examined ticks, while "Candidatus R. rara" was found more frequently in H. concinna (3.0%) compared to H. japonica ticks (1.1%). In this study, "Candidatus R. principis" and "Candidatus R. rara" were characterized for the first time by the 16S rRNA, ompA, ompB, and sca4 genes.

Identification of tick-borne pathogen diversity by metagenomic analysis in Haemaphysalis longicornis from Xinyang, China

Background

A wide variety of pathogens could be maintained and transmitted by Haemaphysalis longicornis. The aim of this study is to systematically examine the variety of pathogens carried by Haemaphysalis longicornis, an importnatn vector, in tick-borne diseases epidemic area, and to estimate the risk of human infection imposed by tick bites.

Methods

Adult questing ticks were collected in Xinyang, central China. Genomic DNA and RNA were extracted from 144 H. longicornis ticks individually, and sequenced respectively as the templates for high-throughput sequencing. Clean reads were compared against the database of NCBI nucleotide collection and specific PCR was performed to confirm the presence of pathogen. Phylogenetic analysis was performed to explore the evolutionary status of pathogens.

Results

The assignment of reads to taxa based on BLASTN results revealed the existence of several potential pathogens, including Anaplasma spp., Rickettsia spp., Babesia sp., as well as severe fever with thrombocytopenia syndrome bunyavirus (SFTSV). Comfirmantory PCR assays revealed the existence of Anaplasma bovis (13/144, 9.03%), Anaplasma centrale (2/144, 1.39%), Rickettsia heilongjiangensis (3/144, 2.08%), Rickettsia sp. LON-13 (1/144, 0.69%), Rickettsia raoultii (5/144, 3.47%), Babesia sp. (1/144, 0.69%). SFTSV accounted for the highest detected pathogen with a positive rate of 18.75% (27/144). Three of the ticks (2.08%) were co-infected with SFTSV and A. bovis.

Conclusion

Our study provided a broadened list of microorganism that harbored by H. longicornis. In previously unrecognized endemic regions, prokaryotic and eukaryotic infection including Anaplasma spp., Rickettsiae spp., and Babesia spp. should be considered, along with the well-known SFTSV for patients with tick bites history. A novel Babesia species was identified in local natural foci, which needs further investigation in the future.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0417-4) contains supplementary material, which is available to authorized users.

Landscape of emerging and re-emerging infectious diseases in China: impact of ecology, climate, and behavior

For the past several decades, the infectious disease profile in China has been shifting with rapid developments in social and economic aspects, environment, quality of food, water, housing, and public health infrastructure. Notably, 5 notifiable infectious diseases have been almost eradicated, and the incidence of 18 additional notifiable infectious diseases has been significantly reduced. Unexpectedly, the incidence of over 10 notifiable infectious diseases, including HIV, brucellosis, syphilis, and dengue fever, has been increasing. Nevertheless, frequent infectious disease outbreaks/events have been reported almost every year, and imported infectious diseases have increased since 2015. New pathogens and over 100 new genotypes or serotypes of known pathogens have been identified. Some infectious diseases seem to be exacerbated by various factors, including rapid urbanization, large numbers of migrant workers, changes in climate, ecology, and policies, such as returning farmland to forests. This review summarizes the current experiences and lessons from China in managing emerging and re-emerging infectious diseases, especially the effects of ecology, climate, and behavior, which should have merits in helping other countries to control and prevent infectious diseases.

Human Infection with Novel Spotted Fever Group Rickettsia Genotype, China, 2015

Only 4 species of spotted fever group rickettsiae have been detected in humans in China. However, phylogenetic analysis of samples from 5 ill patients in China indicated infection with a novel spotted fever group Rickettsia, designated Rickettsia sp. XY99. Clinical signs resembled those of severe fever with thrombocytopenia syndrome.

Severe Fever with Thrombocytopenia Syndrome Complicated by Co-infection with Spotted Fever Group Rickettsiae, China

During 2013–2015 in central China, co-infection with spotted fever group rickettsiae was identified in 77 of 823 patients infected with severe fever with thrombocytopenia syndrome virus. Co-infection resulted in delayed recovery and increased risk for death, prompting clinical practices in the region to consider co-infection in patients with severe fever with thrombocytopenia syndrome.

Distribution and molecular characteristics of rickettsiae found in ticks across Central Mongolia

Background

Little is known regarding tick-borne diseases in Mongolia, despite having 26% of the population still living nomadic pastoral lifestyles. A total of 1497 adult unfed ticks: 261 Ixodes persulcatus, 795 Dermacentor nuttalli, and 441 Hyalomma asiaticum, were collected from three ecologically distinct regions in Central Mongolia. Tick pools (n = 299) containing ~5 ticks each, were tested for Rickettsia and Tick-borne encephalitis virus (TBEV) using nested polymerase chain reaction, reverse transcription-PCR, and quantitative real-time RT-PCR.

Results

Assays yielded pooled prevalence of 92.5% (49/53) and 1.9% (1/53) for pooled I. persulcatus testing positive for “Candidatus Rickettsia tarasevichiae” and TBEV, respectively, while Rickettsia raoultii was found in 72.8% (115/158) of pooled D. nuttalli samples. When calculating a maximum likelihood estimation, an estimated 46.6% (95% CI: 35.2–63.6%) of I. persulcatus ticks in the pooled sample were infected with “Candidatus R. tarasevichiae”.

Conclusions

Both “Candidatus R. tarasevichiae” and R. raoultii are recognized as emerging tick-borne pathogens, with this being one of the first reports of “Candidatus R. tarasevichiae” in Mongolia. Given that “Candidatus R. tarasevichiae” shares the same vector (I. persulcatus) as TBEV, and infections may present with similar symptoms, Mongolian physicians treating suspected cases of TBEV should include “Candidatus R. tarasevichiae” infection in their differential diagnosis and consider prescribing antimicrobial therapy.

Prevalence of Severe Febrile and Thrombocytopenic Syndrome Virus, Anaplasma spp. and Babesia microti in Hard Ticks (Acari: Ixodidae) from Jiaodong Peninsula, Shandong Province

The presence of tick-borne pathogens and their possible coinfections were evaluated among host-seeking ticks in seven cities from Jiaodong peninsula, Shandong Province, with specific PCR or reverse transcription-PCR tests. Among 2107 ticks collected, four species of three genera were identified with Haemaphysalis longicornis as predominant species, and total of 63 H. longicornis and 10 Rhicephalus microplus were confirmed infected with tick-borne pathogens. These pathogens were consequently identified as severe febrile and thrombocytopenic syndrome virus (SFTSV), Anaplasma capra, Anaplasma phygocytophilum, and Babesia microti, respectively, with high phylogenetic scores on some fragments of species-specific genes. The infection rates of the pathogens in H. longicornis were presented as 1.03%, 0.84%, 0.58%, and 1.66%, respectively, close related to its field density and clump distribution pattern. Furthermore, coinfection of A. capra and SFTSV was also discovered from two female H. longicornis in Pingdu city. These results indicated that the potential human pathogens other than severe febrile and thrombocytopenic syndrome might be transmitted by hard ticks separately or in combination, and more reliable differential diagnosis, proper administrations, rational prevention, and control measures should be developed with the support of precision laboratory tests.

Genetic variability of Rickettsia spp. in Ixodes persulcatus ticks from continental and island areas of the Russian Far East

Rickettsia spp. are intracellular Gram-negative bacteria transmitted by arthropods. Two potentially pathogenic rickettsiae, Candidatus Rickettsia tarasevichiae and Rickettsia helvetica, have been found in unfed adult Ixodes persulcatus ticks. The aim of this study was to assess the prevalence and genetic variability of Rickettsia spp. in I. persulcatus ticks collected from different locations in the Russian Far East. In total, 604 adult I. persulcatus ticks collected from four sites in the Khabarovsk Territory (continental area) and one site in Sakhalin Island were examined for the presence of Rickettsia spp. by real-time PCR. Nested PCR with species-specific primers and sequencing were used for genotyping of revealed rickettsiae. The overall prevalence of Rickettsia spp. in ticks collected in different sites varied from 67.9 to 90.7%. However, the proportion of different Rickettsia species observed in ticks from Sakhalin Island significantly differed from that in ticks from the Khabarovsk Territory. In Sakhalin Island, R. helvetica prevailed in examined ticks, while Candidatus R. tarasevichiae was predominant in the Khabarovsk Territory. For gltA and ompB gene fragments, the sequences obtained for Candidatus R. tarasevichiae from all studied sites were identical to each other and to the known sequences of this species. According to sequence analysis of gltA, оmpB and sca4 genes, R. helvetica isolates from Sakhalin Island and the Khabarovsk Territory were identical to each other, but they differed from R. helvetica from other regions and from those found in other tick species. For the first time, DNA of pathogenic Rickettsia heilongjiangensis was detected in I. persulcatus ticks in two sites from the Khabarovsk Territory. The gltA, ompA and оmpB gene sequences of R. heilongjiangensis were identical to or had solitary mismatches with the corresponding sequences of R. heilongjiangensis found in other tick species.