Tsutsugamushi disease was first described in China by Hong Ge in 313. In his book Zhouhou Beiji Fang, three eschar-associated febrile diseases were described: Shashidu, Zhongxidu, and Shegongdu. Shashidu was identified as being identical to tsutsugamushi disease in Japan: it occurred in riverside areas, exhibited an eschar, and was transmitted by tiny red "sand lice". The nature of Zhongxidu remains unknown, but we propose that it is another type of Orientia tsutsugamushi infection: it occurred in mountainous areas, an eschar was observed, and the causative vector was not identified. Moreover, Zhongxidu would have predated Shashidu by five centuries; thus, the first documentation of tsutsugamushi disease would date back 2.2 millennia. O. tsutsugamushi infection without eschar has not been identified in ancient Chinese literature and may be included in Shanghan. Several ancient Chinese books describe that Shegongdu occurs following a Shegong bite. Shegong is described as a bug resembling a cockroach or cicada with a crossbow-like structure, possibly the hypostome and unfolded palps of tick, in its mouth. Thus, Shegong refers to an engorged tick and Shegongdu is a tick-borne rickettsiosis. However, due to a lack of entomological knowledge, these findings have not been recognized for the past 1.7 millennia. 

Tick-Borne Rickettsiosis and Tsutsugamushi Disease Recorded in 313

Ticks are one of the most important vectors that can transmit pathogens to animals and human beings. This study investigated the dominant tick-borne bacteria carried by ticks and tick-borne infections in forestry populations in Arxan, Inner Mongolia, China. Ticks were collected by flagging from May 2020 to May 2021, and blood samples were collected from individuals at high risk of acquiring tick-borne diseases from March 2022 to August 2023. The pooled DNA samples of ticks were analyzed to reveal the presence of tick-borne bacteria using high-throughput sequencing of the 16S rDNA V3–V4 region, and species-specific polymerase chain reaction (PCR) related to sequencing was performed to confirm the presence of pathogenic bacteria in individual ticks and human blood samples. All sera samples were examined for anti-SFGR using ELISA and anti-B. burgdorferi using IFA and WB. A total of 295 ticks (282 Ixodes persulcatus and 13 Dermacentor silvarum) and 245 human blood samples were collected. Rickettsia, Anaplasma, Borrelia miyamotoi, and Coxiella endosymbiont were identified in I. persulcatus by high-throughput sequencing, while Candidatus R. tarasevichiae (89.00%, 89/100), B. garinii (17.00%, 17/100), B. afzelii (7.00%, 7/100), and B. miyamotoi (7.00%, 7/100) were detected in I. persulcatus, as well the dual co-infection with Candidatus R. tarasevichiae and B. garinii were detected in 13.00% (13/100) of I. persulcatus. Of the 245 individuals, B. garinii (4.90%, 12/245), R. slovaca (0.82%, 2/245), and C. burnetii (0.41%, 1/245) were detected by PCR, and the sequences of the target genes of B. garinii detected in humans were identical to those detected in I. persulcatus. The seroprevalence of anti-SFGR and anti-B. burgdorferi was 5.71% and 13.47%, respectively. This study demonstrated that Candidatus R. tarasevichiae and B. garinii were the dominant tick-borne bacteria in I. persulcatus from Arxan, and that dual co-infection with Candidatus R. tarasevichiae and B. garinii was frequent. This is the first time that B. miyamotoi has been identified in ticks from Arxan and R. solvaca has been detected in humans from Inner Mongolia. More importantly, this study demonstrated the transmission of B. garinii from ticks to humans in Arxan, suggesting that long-term monitoring of tick-borne pathogens in ticks and humans is important for the prevention and control of tick-borne diseases.

Surveillance of tick-borne bacteria infection in ticks and forestry populations in Inner Mongolia, China

Abstract Background: Emerging tick-borne bacterial pathogens pose a threat to public health. The bacterial community and diversity in ticks have been reported with high-throughput sequencing methods that have been widely used in microorganism identification. Tick-borne bacterial pathogens such as Rickettsia, Ehrlichia, Coxiella, and Bartonella amplified by PCR methods have been reported in Guizhou. Little information has been reported on the diversity of the bacterial community in ticks in the areas. The aim of this study was to explore the diversity of the bacterial community in ticks from Guizhou Province, southwestern China. Methods: Ticks were collected in the mountainous areas of three counties in Guizhou Province from 2019-2022. Tick species were identified by morphology and molecular biology. DNA was extracted from tick samples, followed by high-throughput sequencing of the full-length 16S rRNA gene to analyze the diversity of the bacterial community of ticks. Results: A total of 554 ticks were captured, including 453 Rhipicephalus microplus and 101 Haemaphysalis longicornis, from cattle and sheep in Ziyun, Shibing, and Luodian Counties. In total, 823 operational taxonomic units (OTUs) were identified with 13 phyla, 22 classes, 55 orders, 121 families, and 253 genera of bacteria. The dominant bacterial genera were Staphylococcus , Pseudomonas , and Stenotrophomonas . We noticed that Rickettsia and Coxiella were abundant in the samples collected from Luodian County. Other tick-borne pathogens, such as Bartonella, Yersinia, Brucella, Anaplasma , and Francisella, were distinguished in the ticks. Conclusions: These results helped us to understand the diversity of the bacterial community in ticks in Guizhou mountain areas. Further studies are needed to uncover the pathogenicity of these tick-carried bacteria and their potential public health threats. 

Detection of bacteria carried by ticks from the mountain areas of Guizhou, Southwestern China

Additional file 1: Figure S1. Phylogenetic trees based on the nucleotide sequences of 23S rRNA gene of Candidatus Anaplasma mongolica. 

Additional file 1 of Molecular surveillance reveals a potential hotspot of tick-borne disease in Yakeshi City, Inner Mongolia

The obligate endosymbiont Candidatus Lariskella (Alphaproteobacteria, Candidatus Midichloriaceae) has been found across a wide diversity of terrestrial arthropods, including ticks, true bugs, beetles, fleas, wasps and moths. However, to date, Ca. Lariskella had never been detected in nematodes or marine animals. Here we report the first known occurrence of Ca. Lariskella infecting a population of marine nematodes (Enoplida, Thoracostomopsideae). This nematode-infecting Ca. Lariskella is closely related to insect-infecting Ca. Lariskella, despite the drastic shift in both host phylum and habitat. TEM and FISH microscopy showed Ca. Lariskella is localized within both somatic cells and developing oocytes, strongly suggesting that Ca. Lariskella is a vertically transmitted endosymbiont within the nematode population. We found that Ca. Lariskella was present within approximately 20% of the nematode population, but notably failed to detect any Ca. Lariskella within adult males, potentially hinting at reproductive manipulation. Overall, our findings show that Ca. Lariskella is not limited to arthropods or terrestrial hosts, indicating a larger host range than previously described. Its presence within marine nematodes demonstrates the ability of Ca. Lariskella to infect nematode hosts, as well as hosts from marine environments, suggesting terrestrial nematodes, marine arthropods, and perhaps even other marine invertebrates could be potential hosts of Ca. Lariskella. 

A Midichloriaceae endosymbiont of terrestrial arthropods found as an endosymbiont in a marine nematode

Mosquitoes are generally recognized as the most important vector of many zoonotic pathogens. In this study, seven mosquitoes species were identified (Anopheles pullus, Anopheles sinensis, Anopheles lesteri, Anopheles kleini, Ochlerotatus dorsalis, Aedes koreicus and Culex inatomii) in samples collected from Yingkou City, Liaoning Province, Northeastern China. A novel Rickettsia species was detected in Anopheles sinensis (two of 71, 2.82%) and Anopheles pullus (one of 106, 0.94%) mosquitoes. Genetic analysis indicated that the rrs and ompB genes have highest 99.60% and 97.88%-98.14% identities to Rickettsia felis, an emerging human pathogen of global concern mainly harboured by fleas, mosquitoes and booklice. The gltA sequences of these strains have 99.72% of nucleotide similarity with Rickettsia endosymbiont of Medetera jacula. The groEL sequences have 98.37% similarity to both Rickettsia tillamookensis and Rickettsia australis. The htrA sequences have 98.77% similarity to Rickettsia lusitaniae. In the phylogenetic tree based on concatenated nucleotide sequences of rrs, gltA, groEL, ompB and htrA genes, these strains are closely related to R. felis. Herein, we name it 'Candidatus Rickettsia yingkouensis'. Its human pathogenicity to humans and animals is still to be determined.

A novel Rickettsia species closely related to Rickettsia felis in Anopheles mosquitoes from Yingkou City, Northeast China.

During 2021, 403 ticks including Haemaphysalis qinghaiensis, Ixodes ovatus, Ixodes acutitarsus, and Rhipicephalus microplus were collected from three sites (590, 310, and 576 km away from each other) in Sichuan Province, China. A total of nine Rickettsiales species were identified in them, including three Rickettsia spp., five Anaplasma spp., and one Ehrlichia sp. Anaplasma ovis and a novel Rickettsia sp. named “Candidatus Rickettsia liangshanensis” were characterized in I. ovatus ticks from Liangshan, with positive rates of 11.11% and 45.56%, respectively. Anaplasma capra (13.33%) and Anaplasma bovis (15.33%) were detected in H. qinghaiensis ticks from Maerkang. Phylogenetic analysis based on 16S rRNA, gltA, and groEL gene sequences indicated that the A. bovis strains were divided into two groups. Additionally, a novel Ehrlichia species named “Candidatus Ehrlichia maerkangensis” was identified. It is closely related to “Candidatus Ehrlichia zunyiensis” which was previously reported in Berylmys bowersi rats from Zunyi City, Southwest China. In R. microplus from Mianyang, “Candidatus Rickettsia jingxinensis” was detected with a high prevalence (92.99%). Notably, a variant of R. raoultii was identified in I. acutitarsus (33.33%). This may be the first Rickettsiales bacterium reported in I. acutitarsus. Our results reveal the remarkable biodiversity of Rickettsiales in this area. Some of these bacteria are human pathogens, indicating the potential exposure risk to local people. 

Circulation of multiple rickettsiales bacteria in ticks from sichuan province, Southwest China.

Rickettsiales (Rickettsia spp., Ehrlichia spp., and Anaplasma spp., etc.) are generally recognized as potentially emerging tick-borne pathogens. However, some bacteria and areas in China remain uninvestigated. In this study, we collected 113 ticks from mammals in Guizhou Province, Southwest China, and screened for the Rickettsiales bacteria. Subsequently, two spotted fever group Rickettsia species and one Candidatus Lariskella sp. were detected and characterized. “Candidatus Rickettsia jingxinensis” was detected in Rhipicephalus microplus (1/1), Haemaphysalis flava (1/3, 33.33%), Haemaphysalis kitaokai (1/3), and Ixodes sinensis (4/101, 3.96%), whereas Rickettsia monacensis was positive in H. flava (1/3), H. kitaokai (2/3), and I. sinensis ticks (74/101, 73.27%). At least two variants/sub-genotypes were identified in the R. monacensis isolates, and the strikingly high prevalence of R. monacensis may suggest a risk of human infection. Unexpectedly, a Candidatus Lariskella sp. belonging to the family Candidatus Midichloriaceae was detected from Ixodes ovatus (1/4) and I. sinensis (10/101, 9.90%). The gltA and groEL gene sequences were successfully obtained, and they show the highest (74.63–74.89% and 73.31%) similarities to “Candidatus Midichloria mitochondrii”, respectively. Herein, we name the species “Candidatus Lariskella guizhouensis”. These may be the first recovered gltA and groEL sequences of the genus Candidatus Lariskella.

/pdf/prevalence-of-spotted-fever-group-rickettsia-and-candidatus-19xtzcye.pdf

Prevalence of Spotted Fever Group Rickettsia and Candidatus Lariskella in Multiple Tick Species from Guizhou Province, China

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A novel Rickettsia species closely related to Rickettsia felis in Anopheles mosquitoes from Yingkou City, Northeast China.

Circulation of multiple rickettsiales bacteria in ticks from sichuan province, Southwest China.

Prevalence of Spotted Fever Group Rickettsia and Candidatus Lariskella in Multiple Tick Species from Guizhou Province, China