Molecular Characteristics of Rickettsia in Ticks Collected along the Southern Border of Mongolia

Tick-borne pathogens in Mongolian ticks: The high prevalence of Rickettsia raoultii and its public health implications

In Mongolia, a substantial segment of the population is engaged in pastoralism, leading to frequent interactions with livestock and heightened exposure to tick-infested environments. Consequently, ticks and the endemic tick-borne pathogens (TBPs) they harbor present significant health threats. In May 2021, we conducted a study to evaluate the prevalence of 9 TBPs in ticks collected from four regions in Mongolia: Uvurkhangai, Tuv, Bayan-Ulgii, and Khentii. The pathogens surveyed included Anaplasma, Rickettsia, Bartonella, Borrelia, Ehrlichia, Babesia, Toxoplasma, Theileria, and lumpy skin disease virus. Molecular analysis of 1142 ticks revealed that, although the majority of TBPs were not detected, 89.1 % of the ticks were positive for Rickettsia. Genetic characterization using the 16S rRNA and gltA genes identified the pathogen identified the pathogen Rickettsia raoultii. Species identification indicated a predominance of Dermacentor nuttalli (70.0 %) and Dermacentor silvarum (30.0 %). These findings highlight the extensive prevalence of R. raoultii in Mongolia and underscore the urgent need for heightened awareness and preventive measures due to the high level of interaction between livestock and humans. The genetic similarity of R. raoultii sequences to those found in neighboring countries suggests potential cross-border transmission, underscoring the importance of conducting similar research in surrounding regions. This study advances our understanding of the epidemiology of tick-borne diseases in Mongolia and can inform public health strategies aimed at mitigating the risks associated with these infections.

Applying next generation sequencing to detect tick-pathogens in Dermacentor nuttalli, Ixodes persulcatus, and Hyalomma asiaticum collected from Mongolia

Ticks and tick-borne diseases represent major threats to the public health of the Mongolian population, of which an estimated 26% live a traditional nomadic pastoralist lifestyle that puts them at increased risk for exposure. Ticks were collected by dragging and removal from livestock in Khentii, Selenge, Tuv, and Umnugovi aimags (provinces) during March-May 2020. Using next-generation sequencing (NGS) with confirmatory PCR and DNA sequencing, we sought to characterize the microbial species present in Dermacentor nuttalli (n = 98), Hyalomma asiaticum (n = 38), and Ixodes persulcatus (n = 72) tick pools. Rickettsia spp. were detected in 90.4% of tick pools, with Khentii, Selenge, and Tuv tick pools all having 100% pool positivity. Coxiella spp. were detected at an overall pool positivity rate of 60%, while Francisella spp. were detected in 20% of pools and Borrelia spp. detected in 13% of pools. Additional confirmatory testing for Rickettsia-positive pools demonstrated Rickettsia raoultii (n = 105), Candidatus Rickettsia tarasevichiae (n = 65) and R. slovaca/R. sibirica (n = 2), as well as the first report of Candidatus Rickettsia jingxinensis (n = 1) in Mongolia. For Coxiella spp. reads, most samples were identified as a Coxiella endosymbiont (n = 117), although Coxiella burnetii was detected in eight pools collected in Umnugovi. Borrelia species that were identified include Borrelia burgdorferi sensu lato (n = 3), B. garinii (n = 2), B. miyamotoi (n = 16), and B. afzelii (n = 3). All Francisella spp. reads were identified as Francisella endosymbiont species. Our findings emphasize the utility of NGS to provide baseline data across multiple tick-borne pathogen groups, which in turn can be used to inform health policy, determine regions for expanded surveillance, and guide risk mitigation strategies.

Crimean-Congo hemorrhagic fever virus in Central, Eastern, and South-eastern Asia

Crimean-Congo hemorrhagic fever (CCHF), caused by Crimean-Congo hemorrhagic fever virus (CCHFV), is endemic in Africa, Asia, and Europe, but CCHF epidemiology and epizootiology is only rudimentarily defined for most regions. Here we summarize what is known about CCHF in Central, Eastern, and South-eastern Asia. Searching multiple international and country-specific databases using a One Health approach, we defined disease risk and burden through identification of CCHF cases, anti-CCHFV antibody prevalence, and CCHFV isolation from vector ticks. We identified 2313 CCHF cases that occurred in 1944-2021 in the three examined regions. Central Asian countries reported the majority of cases (2,026). In Eastern Asia, China was the only country that reported CCHF cases (287). In South-eastern Asia, no cases were reported. Next, we leveraged our previously established classification scheme to assign countries to five CCHF evidence levels. Six countries (China, Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, and Uzbekistan) were assigned to level 1 or level 2 based on CCHF case reports and the maturity of the countries' surveillance systems. Two countries (Mongolia and Myanmar) were assigned to level 3 due to evidence of CCHFV circulation in the absence of reported CCHF cases. Thirteen countries in Eastern and South-eastern Asia were categorized in levels 4 and 5 based on prevalence of CCHFV vector ticks. Collectively, this paper describes the past and present status of CCHF reporting to inform international and local public-health agencies to strengthen or establish CCHFV surveillance systems and address shortcomings.

Comparative analysis of microbial communities in different growth stages of Dermacentor nuttalli

Ticks were identified as arthropods that are pathogenic vectors. Dermacentor nuttalli is one of the dominant tick species in Inner Mongolia, and it carries and transmits a wide range of pathogenic microorganisms. However, at present, only the detection of D. nuttalli adult ticks and D. nuttalli different developmental stages carrying one specific pathogen, or the next-generation sequencing of D. nuttalli adult ticks were available. In this study, we investigated the microbial community structures of D. nuttalli in different growth stages under laboratory artificial feeding conditions. Total DNA was extracted from seven growth stages (female adult ticks, eggs, larval ticks, engorged larval ticks, nymphal ticks, engorged nymphal ticks, and second-generation adult ticks) obtained from laboratory artificial feeding of engorged D. nuttalli female ticks in Inner Mongolia. Then, the 16S rDNA V3-V4 hypervariable region was amplified to construct an Illumina PE250 library. Finally, 16S rRNA sequencing was performed on Illumina Novaseq 6000 platform. The sequencing data were analyzed using molecular biology software and platforms. The Illumina PE250 sequencing results showed that the egg stage had the highest diversity and number of species (28.74%, 98/341), while the engorged nymph stage had the lowest diversity and number of species (9.72%, 21/216). A total of 387 genera of 22 phyla were annotated in D. nuttalli, with 9 phyla and 57 genera found throughout all 7 growth stages. The dominant phylum was Proteobacteria; the dominant genera were Arsenophonus and Rickettsia; and the genera with the highest relative abundance in the 7 growth stages were Pseudomonas, Paenalcaligenes, Arsenophonus, Arsenophonus, Pseudomonas, Arsenophonus, and Rickettsia, respectively. Among the 23 exact species annotated, Brucella melitensis exhibits pathogeny that poses a serious threat to humans and animals. In this study, the microbial community composition at different growth stages of D. nuttalli was comprehensively analyzed for the first time.

Metagenomic profiles of Dermacentor tick pathogens from across Mongolia, using next generation sequencing

Tick-borne diseases are a major public health concern in Mongolia. Nomadic pastoralists, which make up ~ 26% of Mongolia’s population, are at an increased risk of both tick bite exposure and economic loss associated with clinical disease in herds. This study sought to further characterize tick-borne pathogens present in Dermacentor ticks (n = 1,773) sampled in 2019 from 15 of Mongolia’s 21 aimags (provinces). The ticks were morphologically identified and sorted into 377 pools which were then screened using Next-Generation Sequencing paired with confirmatory PCR and DNA sequence analysis. Rickettsia spp. were detected in 88.33% of pools, while Anaplasma spp. and Bartonella spp. were detected in 3.18 and 0.79% of pools, respectively. Khentii had the highest infection rate for Rickettsia spp. (76.61%; CI: 34.65–94.79%), while Arkhangai had the highest infection rate for Anaplasma spp. (7.79%; CI:4.04–13.72%). The exclusive detection of Anaplasma spp. in tick pools collected from livestock supports previous work in this area that suggests livestock play a significant role in disease maintenance. The detection of Anaplasma, Bartonella, and Rickettsia demonstrates a heightened risk for infection throughout Mongolia, with this study, to our knowledge, documenting the first detection of Bartonella melophagi in ticks collected in Mongolia. Further research deploying NGS methods is needed to characterize tick-borne pathogens in other endemic tick species found in Mongolia, including Hyalomma asiaticum and Ixodes persulcatus.

Co-infections with multiple pathogens in natural populations of Ixodes persulcatus ticks in Mongolia

Background

In Mongolia, the taiga tick Ixodes persulcatus is the major vector of tick-borne pathogens. Knowledge about co-infections of these pathogens in ticks is necessary both for understanding their persistence in nature and for diagnosing and treating tick-borne diseases.

Methods

The prevalence of seven tick-borne infections in 346 I. persulcatus collected from the Selenge and Bulgan provinces of Mongolia was evaluated using real-time PCR. Quantification of Borrelia spp. was performed using multiplex quantitative PCR targeting the 16S rRNA gene. Genetic analysis of Borrelia spp. in 11 ticks infected with Borrelia miyamotoi, including six ticks co-infected with Borrelia burgdorferi sensu lato (s.l.), was performed by high-throughput sequencing of the flaB gene fragment.

Results

Six ticks (1.7%) were infected with tick-borne encephalitis virus (TBEV); 171 (49.4%), with B. burgdorferi sensu lato; 17 (4.9%), with B. miyamotoi; 47 (13.6%), with Anaplasma phagocytophilum; and 56 (16.2%), with Ehrlichia sp. Neither Rickettsia sibirica nor R. heilongjiangensis were detected. Borrelia burgdorferi s.l. occurred as co-infection in 55 (32.2%) of all infected ticks. The other pathogens co-infected ticks in 58.8–70.2% of cases. No pairwise associations between co-infecting pathogens were observed, with the exception of a positive association between A. phagocytophilum and Ehrlichia sp. infections. The spirochete loads of B. miyamotoi were significantly higher than those of B. burgdorferi s.l. (mean: 5.2 vs 4.0 log10 genome copies/tick, respectively). Ten isolates of B. miyamotoi belonged to the Siberian lineage. Borrelia burgdorferi s.l was represented by nine isolates of B. afzelii, B. bavariensis and B. garinii.

Conclusions

In populations of I. persulcatus inhabiting the Selenge and Bulgan provinces of Mongolia, five vector-borne pathogens, i.e. TBEV, B. burgdorferi s.l., B. miyamotoi, A. phagocytophilum and Ehrlichia sp., persist independently from each other, with the exception of A. phagocytophilum and Ehrlichia sp. which seem to share the circulation mode. The discrepancies in B. burgdorferi s.l. and B. miyamotoi prevalence and spirochete load per tick suggest that different ecological niches are occupied by Lyme disease and relapsing fever agents. High-throughput sequencing allows genetic identification of borreliae species in co-infected ticks.

Graphical Abstract

Ehrlichia chaffeensis and Four Anaplasma Species With Veterinary and Public Health Significance Identified in Tibetan Sheep (Ovis aries) and Yaks (Bos grunniens) in Qinghai, China

Tick-borne diseases (TBDs) can cause serious economic losses and are very important to animal and public health. To date, research on TBDs has been limited in Qinghai-Tibet Plateau, China. This epidemiological investigation was conducted to evaluate the distribution and risk factors of Anaplasma spp. and Ehrlichia chaffeensis in livestock in Qinghai. A total of 566 blood samples, including 330 yaks (Bos grunniens) and 236 Tibetan sheep (Ovis aries) were screened. Results showed that A. bovis (33.3%, 110/330) and A. phagocytophilum (29.4%, 97/330) were most prevalent in yaks, followed by A. ovis (1.2%, 4/330), A. capra (0.6%, 2/330), and E. chaffeensis (0.6%, 2/330). While A. ovis (80.9%, 191/236) and A. bovis (5.1%, 12/236) infection was identified in Tibetan sheep. To our knowledge, it is the first time that A. capra and E. chaffeensis have been detected in yaks in China. Apart from that, we also found that co-infection of A. bovis and A. phagocytophilum is common in yaks (28.2%, 93/330). For triple co-infection, two yaks were infected with A. bovis, A. phagocytophilum, and A. capra, and two yaks were infected with A. bovis, A. phagocytophilum, and E. chaffeensis. Risk analysis shows that infection with A. bovis, A. phagocytophilum, and A. ovis was related to region and altitude. This study provides new data on the prevalence of Anaplasma spp. and E. chaffeensis in Qinghai, China, which may help to develop new strategies for active responding to these pathogens.