Molecular investigation of tick-borne pathogens in ticks removed from tick-bitten humans in the southwestern region of the Republic of Korea

16S rRNA metabarcoding for the identification of tick-borne bacteria in ticks in the Republic of Korea

Ticks are blood-sucking ectoparasites that act as vectors for transmission of various pathogens. The purpose of this study was to assess tick-borne bacteria, whether pathogenic or not, in ticks distributed in Korea using 16S rRNA metabarcoding and to confirm the results by PCR. Questing ticks were collected from four provinces in Korea in 2021 using the flagging method. After pooling the DNAs from the 61 tick pools (including 372 ticks), the bacterial 16S rRNA V3-V4 hypervariable region was amplified and sequenced using the MiSeq platform. Rickettsia, Ehrlichia, and the endosymbiont Wolbachia were confirmed by conventional PCR and molecular analysis. In total, 6907 ticks (534 pools) were collected and identified as belonging to five species (Haemaphysalis spp., H. longicornis, H. flava, I. nipponensis, and A. testudinarium). Through 16S rRNA metabarcoding, 240 amplicon sequence variants were identified. The dominant taxa were Rickettsiella and Coxiella. Additionally, pathogenic bacteria such as Rickettsia and Ehrlichia, endosymbiotic bacteria such as Wolbachia and Spiroplasma were identified. Polymerase chain reaction (PCR) was performed to confirm the presence of Rickettsia, Ehrlichia, Bartonella, and Wolbachia in individual ticks. Overall, 352 (65.92%) of 534 pools tested positive for at least one of the screened tick-borne bacteria. Rickettsia was the most prevalent (61.42%), followed by Wolbachia (5.05%). Ehrlichia was detected in 4.86% of tested samples, whereas Bartonella was not detected. In this study, 16S rRNA metabarcoding revealed the presence of Rickettsia, Wolbachia, and Ehrlichia, in that order of abundance, while showing absence of Bartonella. These results were confirmed to exhibit the same trend as that of the conventional PCR. Therefore, large-scale screening studies based on pooling, as applied in this study, will be useful for examining novel or rare pathogens present in various hosts and vectors.

Molecular Identification of Spotted Fever Group Rickettsiae in Ticks in the Republic of Korea

The Rickettsia species transmitted by ticks are mostly classified within the spotted fever group rickettsiae (SFGR), which causes tick-borne rickettsiosis. Although efforts have been made to investigate their prevalence in the Republic of Korea (ROK), research has been limited to certain areas. Furthermore, the pooling method for ticks does not fully reflect the exact infection rate. Therefore, we aimed to perform molecular identification of SFGR in ticks to elucidate the current prevalence of tick-borne rickettsiosis in the ROK. The SFGR of ticks was identified using polymerase chain reaction targeting the 17 kDa antigen, ompA, and gltA, followed by sequencing for species identification and phylogenetic analysis. In total, 302 ticks belonging to four species (Haemaphysalis flava, H. longicornis, Ixodes nipponensis, and Amblyomma testudinarium) were collected between April and November 2022. The overall SFGR infection rate was 26.8% (81/302 patients). Both adult and nymphal ticks and the SFGR infection rate increased during April-May, reaching their peaks in June, followed by a marked decline in August and July, respectively. Phylogenetic analysis revealed three species (R. monacensis, R. heilongjiangensis, and Candidatus R. jingxinensis) of SFGR. Thus, our results emphasize the importance of tick surveys for the prevention and management of tick-borne rickettsiosis.

Distribution and pathogen prevalence of field-collected ticks from south-western Korea: a study from 2019 to 2022

Hard ticks are known vectors of various pathogens, including the severe fever with thrombocytopenia syndrome virus, Rickettsia spp., Coxiella burnetii, Borrelia spp., Anaplasma phagocytophilum, and Ehrlichia spp. This study aims to investigate the distribution and prevalence of tick-borne pathogens in southwestern Korea from 2019 to 2022. A total of 13,280 ticks were collected during the study period, with H. longicornis accounting for 86.1% of the collected ticks. H. flava, I. nipponensis and A. testudinarium comprised 9.4%, 3.6%, and 0.8% of the ticks, respectively. Among 983 pools tested, Rickettsia spp. (216 pools, 1.6% MIR) were the most prevalent pathogens across all tick species, with R. japonica and R. monacensis frequently detected in I. nipponensis and Haemaphysalis spp., respectively. Borrelia spp. (28 pools, 0.2% MIR) were predominantly detected in I. nipponensis (27 pools, 13.8% MIR, P < 0.001). Co-infections, mainly involving Rickettsia monacensis and Borrelia afzelii, were detected in I. nipponensis. Notably, this study identified R. monacensis for the first time in A. testudinarium in South Korea. These findings offer valuable insights into the tick population and associated pathogens in the region, underscoring the importance of tick-borne disease surveillance and prevention measures.

Current Status of Trypanosoma grosi and Babesia microti in Small Mammals in the Republic of Korea

Small mammals, such as rodents and shrews, are natural reservoir hosts of zoonotic diseases, including parasitic protozoa. To assess the risk of rodent-borne parasitic protozoa in the Republic of Korea (ROK), this study investigated the status of parasitic protozoa, namely Trypanosoma, Babesia, and Theileria, in small mammals. In total, 331 blood samples from small mammals were analyzed for parasites using PCR and sequenced. Samples were positive for Trypanosoma grosi (23.9%; n = 79) and Babesia microti (10%; n = 33) but not Theileria. Small mammals from Seogwipo-si showed the highest infection rate of T. grosi (48.4%), while the highest B. microti infection rate was observed in those from Gangneung-si (25.6%). Sequence data revealed T. grosi to be of the AKHA strain. Phylogenetic analysis of B. microti revealed the US and Kobe genotypes. B. microti US-type-infected small mammals were detected throughout the country, but the Kobe type was only detected in Seogwipo-si. To our knowledge, this is the first nationwide survey that confirmed T. grosi and B. microti infections at the species level in small mammals in the ROK and identified the Kobe type of B. microti. These results provide valuable information for further molecular epidemiological studies on these parasites.

Circulation of multiple Rickettsiales bacteria in ticks from Sichuan province, Southwest 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.

Molecular Detection of Anaplasma, Ehrlichia and Rickettsia Pathogens in Ticks Collected from Humans in the Republic of Korea, 2021

Tick-borne pathogens (TBPs), transmitted by the bites of ticks, are of great medical and veterinary importance. They include bacteria, viruses, and protozoan parasites. To provide fundamental data on the risk of tick contact and public health strategies, we aimed to perform a molecular investigation on four tick-borne bacterial pathogens in ticks collected from humans across the Republic of Korea (ROK) in 2021. In total, 117 ticks were collected, including Haemaphysalis longicornis (56.4%), Amblyomma testudinarium (26.5%), Ixodes nipponensis (8.5%), H. flava (5.1%), and I. persulcatus (0.9%). Among the ticks, 20.5% (24/117) contained tick-borne bacterial pathogens, with infection rates of 17.9% for Rickettsia (Candidatus Rickettsia jingxinensis, R. tamurae, R. monacensis, and Candidatus Rickettsia tarasevichiae), 2.5% for Anaplasma (A. phagocytophilum, A. capra, and A. bovis), and 0.9% for Ehrlichia (Ehrlichia sp.). Additionally, the co-detection rate for R. monacensis and A. phagocytophilum was 0.9%. To our knowledge, this is the first report of A. capra and A. bovis detection in ticks collected from humans in the ROK. This study contributes to the understanding of the potential risk of tick contact and provides fundamental data for establishing a public health strategy for tick-borne disease management in the ROK.

Rickettsia sp. and Anaplasma spp. in Haemaphysalis longicornis from Shandong province of China, with evidence of a novel species "Candidatus Anaplasma Shandongensis"

Haemaphysalis longicornis is one of the most dominant and widespread tick species in China. This species mainly infests wild animals and occasionally attacks humans, and has been associated with the transmission of a variety of zoonotic pathogens including spotted fever group Rickettsia (SFGR), severe fever with thrombocytopenia syndrome virus (SFTSV), Anaplasma phagocytophilum, Babesia spp. and Theileria spp.. Although there are increasing reports of various pathogens associated with H. longicornis, some neglected pathogens in certain areas still need to be studied. In this study, a total of 171 H. longicornis ticks were collected from goats in three locations of Shandong Province, Eastern China (Zibo, Linyi, and Qingdao cities), and subsequently screened for the presence of Rickettsia, Anaplasma, and Ehrlichia bacteria. A total of four bacterial species were identified and characterized. "Candidatus Rickettsia jingxinensis" was detected in one tick specimen from Zibo city. Of 98 ticks from Linyi city, 63.27% (62/98) were tested positive for Anaplasma capra and 5.10% (5/98) were positive for Anaplasma bovis. Interestingly, a novel Anaplasma species was detected and characterized in one tick specimen from Zibo and one other from Linyi, respectively. Genetic and phylogenetic analysis based on the 16S, gltA, groEL, and msp4 genes indicated that it was divergent from all known Anaplasma species but mostly related to A. phagocytophilum and "Cadidatus Anaplasma boleense". Based on where it was first detected, we named it "Candidatus Anaplasma shandongensis".

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

High diversity of Rickettsia spp., Anaplasma spp., and Ehrlichia spp. in ticks from Yunnan Province, Southwest China

Rickettsia, Anaplasma, and Ehrlichia belonging to the order Rickettsiales are causative agents of tick-borne diseases in humans. During 2021, 434 ticks including Rhipicephalus microplus and R. haemaphysaloides were collected from three sampling sites in Yunnan Province, Southwest China, and analyzed for the presence of these bacteria. Nine bacterial species were identified, including two Rickettsia spp., three Anaplasma spp., and four Ehrlichia spp., some of which are potential human pathogens. Genetic and phylogenetic analysis on 16S rRNA, gltA, groEL, ompA, ompB, and sca4 genes indicated the presence of a novel spotted fever group Rickettsia (SFGR) named “Candidatus Rickettsia shennongii” in six of the 38 R. haemaphysaloides ticks from two locations, Dehong Autonomous Prefecture and Honghe City. Another SFGR species, Candidatus Rickettsia jingxinensis was detected in ticks from all three sites, with an overall positive rate of 62.67%. Three other human pathogenic species, Anaplasma ovis (1.38%, 6/434), Ehrlichia canis (16.36%, 71/434), and E. chaffeensis (0.23%, 1/434) were detected in these ticks and characterized. Moreover, Ehrlichia sp. (4.84%, 21/434), E. minasensis (7.37%, 32/434), A. marginale (6.91%, 30/434), and Cadidatus Anaplasma boleense (1.15%, 5/434) were detected in R. microplus ticks, for which pathogenicity to humans remains to be determined. The results reveal the remarkable diversity of Rickettsiales bacteria in ticks from Yunnan Province, Southwest China. The high infection rate of some human pathogenic bacteria in ticks may indicate potential infection risk in humans, and it highlights the need for surveillance in local populations.

Molecular Detection of Anaplasma phagocytophilum and Ehrlichia Species in Ticks Removed from Humans in the Republic of Korea

Human granulocytic anaplasmosis (HGA) and human monocytic ehrlichiosis (HME) are zoonotic tick-borne diseases transmitted via tick bites. To determine the state of human Anaplasma and Ehrlichia infections caused by tick bites in the Republic of Korea (ROK), we conducted a nationwide investigation of human cases of tick bites in 2020. A total of 180 ticks were obtained, comprising Haemaphysalis longicornis (70.0%), Amblyomma testudinarium (17.8%), Ixodes nipponensis (6.1%), H. flava (4.4%), and I. persulcatus (1.7%). In three cases (1.7%; 95% CI: 0.3-4.9), A. phagocytophilum was detected in Ixodes ticks using primers for Anaplasma-specific genes (16s rRNA, ankA, and msp4). Conversely, Ehrlichia sp. was only detected in H. longicornis, in two cases (1.1%; 95% CI: 0.1-4.0). To the best of our knowledge, this is the first record of Ehrlichia sp. in ticks parasitizing humans in the ROK. As concerns remain about the possibility of HGA and HME transmission, continuous monitoring and management of the pathogens and vectors are necessary.

Molecular Survey of Vector-Borne Pathogens in Ticks, Sheep Keds, and Domestic Animals from Ngawa, Southwest China

Vector-borne pathogens are mainly transmitted by blood-feeding arthropods such as ticks, mosquitoes, fleas, lice, mites, etc. They pose a significant threat to animal and human health due to their worldwide distribution. Although much work has been performed on these pathogens, some neglected areas and undiscovered pathogens are still to be further researched. In this study, ticks (Haemaphysalis qinghaiensis), sheep keds (Melophagus ovinus), and blood samples from yaks and goats were collected in Ngawa Tibetan and Qiang Autonomous Prefecture located on the eastern edge of the Qinghai–Tibet Plateau, Southwest China. Several vector-borne bacterial pathogens were screened and studied. Anaplasma bovis strains representing novel genotypes were detected in ticks (8.83%, 37/419), yak blood samples (45.71%, 64/140), and goat blood samples (58.93%, 33/56). Two spotted fever group (SFG) Rickettsiae, Candidatus Rickettsia jingxinensis, and a novel Rickettsia species named Candidatus Rickettsia hongyuanensis were identified in ticks. Another Rickettsia species closely related to the Rickettsia endosymbiont of Polydesmus complanatus was also detected in ticks. Furthermore, a Coxiella species was detected in ticks (3.34%, 14/419), keds (1.89%, 2/106), and yak blood (0.71%, 1/140). Interestingly, another Coxiella species and a Coxiella-like bacterium were detected in a tick and a goat blood sample, respectively. These results indicate the remarkable diversity of vector-borne pathogens circulating in this area. Further investigations on their pathogenicity to humans and domestic animals are still needed.

Ticks and Tick-Borne Pathogens in Domestic Animals, Wild Pigs, and Off-Host Environmental Sampling in Guam, USA

Background: Guam, a United States of America (USA) island territory in the Pacific Ocean, is known to have large populations of ticks; however, it is unclear what the risk is to wildlife and humans living on the island. Dog (Canis familiaris), cat (Felis catus), and wild pig (Sus scrofa) sentinels were examined for ticks, and environmental sampling was conducted to determine the ticks present in Guam and the prevalence of tick-borne pathogens in hosts.

Methods and Results: From March 2019-November 2020, ticks were collected from environmental sampling, dogs, cats, and wild pigs. Blood samples were also taken from a subset of animals. A total of 99 ticks were collected from 27 environmental samples and all were Rhipicephalus sanguineus, the brown dog tick. Most ticks were collected during the dry season with an overall sampling success rate of 63% (95% CI: 42.4–80.6). 6,614 dogs were examined, and 12.6% (95% CI: 11.8–13.4) were infested with at least one tick. One thousand one hundred twelve cats were examined, and six (0.54%; 95% CI: 0.20–1.1) were found with ticks. Sixty-four wild pigs were examined and 17.2% (95% CI: 9.5–27.8) had ticks. In total, 1,956 ticks were collected and 97.4% of ticks were R. sanguineus. A subset of R. sanguineus were determined to be the tropical lineage. The other tick species found were Rhipicephalus microplus (0.77%), Amblyomma breviscutatum (0.77 %), and a Haemaphysalis sp. (0.51%). Blood samples from 136 dogs, four cats, and 64 wild pigs were tested using polymerase chain reaction (PCR) and DNA sequencing methods. Five different tick-borne pathogens with the following prevalences were found in dogs: Anaplasma phagocytophilum 5.9% (95% CI: 2.6–11.3); Anaplasma platys 19.1% (95% CI: 12.9–26.7); Babesia canis vogeli 8.8% (95% CI: 4.6–14.9); Ehrlichia canis 12.5% (95% CI: 7.5–19.3); Hepatozoon canis 14.7% (95% CI: 9.2–28.8). E. canis was detected in one cat, and no tick-borne pathogens were detected in wild pigs. Overall, 43.4% (95% CI: 34.9–52.1) of dogs had at least one tick-borne pathogen. Serological testing for antibodies against Ehrlichia spp. and Anaplasma spp. showed prevalences of 14.7% (95% CI: 9.2–28.8) and 31.6% (95% CI: 23.9–40), respectively.

Conclusion: Four different tick species were found in Guam to include a Haemaphysalis sp., which is a previously unreported genus for Guam. Dogs with ticks have a high prevalence of tick-borne pathogens which makes them useful sentinels.