Prevalence of Borrelia burgdorferi sensu lato in ticks from eastern China

Epidemiological characteristics and risk distribution prediction of severe fever with thrombocytopenia syndrome in Zhejiang Province, China

BACKGROUND

Severe fever with thrombocytopenia syndrome (SFTS) is an emerging infectious disease, garnering increasing attention due to rising case numbers and expanding geographical reach. However, there is limited research on the potential factors influencing the distribution of SFTS.

METHODS

Data on SFTS cases in Zhejiang province were obtained from 2011 to 2022. Data on ecoclimatic factors, land cover, and human population density at the county level were also collected. Spatial autocorrelation analysis was used to analyze the epidemic characteristics and spatial clustering. A boosted regression tree (BRT) model was used to assess ecoclimatic and socioenvironmental drivers for the distributions of SFTS.

RESULTS

The SFTS cases increased from 9 in 2011-1,103 in 2022 with an average incidence rate of 0.099 per 100,000. There is an obvious seasonality to SFTS cases, primarily occurring between April and August. We detected global spatial autocorrelation of SFTS cases in all years (P < 0.05) except 2011, 2012 and 2014. Local spatial autocorrelation analysis suggested that the "High-high" agglomeration areas are mainly distributed in the hilly terrain of the east coast of Zhejiang province. Furthermore, factors such as mean temperature of wettest quarter (relative contribution, RC = 18.51%) and annual precipitation (9.29%) were found to have significantly contribution to the occurrence of SFTS. The model-predicted risk areas, particularly in Daishan County (predicted probability of cases: 0.986), Linhai city (0.972), and Tiantai County (0.971), align with reported cases.

CONCLUSIONS

These findings suggested that SFTS incidence has increased and spatially expanded over the past few years. It is necessary to expand the scope and improve the sensitivity of surveillance, especially in western, southern and northern Zhejiang.

Molecular Detection of Tick-Borne Bacterial Pathogens in Ticks and Rodents from the China-Vietnam Border

Ticks and tick-borne diseases constitute a crucial focus for the health of both humans and animals worldwide. Although numerous studies on tick-borne diseases have been conducted in China, reports on tick-borne pathogens in ticks and rodents from the China-Vietnam border are scarce. In this study, we investigated tick-borne bacterial pathogens, including Rickettsia, Anaplasmataceae, and Borrelia, in nine rodents (Rattus norvegicus) and 88 ticks collected from cattle and rodents in Jingxi, a city at the China-Vietnam border. Through molecular detection and sequence analysis, four known tick-borne pathogens were identified. Specifically, Rickettsia japonica was detected in 46.3% (37/80) of Haemaphysalis cornigera; Anaplasma phagocytophilum and Candidatus Neoehrlichia mikurensis were identified in one Ixodes granulatus and one rodent, respectively; and Borrelia valaisiana was detected in two I. granulatus. Additionally, a potentially novel species of Rickettsia, provisionally named Rickettsia sp. JX, was detected in 41.3% (33/80) of Ha. cornigera, one Rhipicephalus microplus, three I. granulatus, and nine rodents, whereas a potentially novel species of Borrelia, tentatively named Borrelia sp. JX, was detected in one I. granulatus. To the best of our knowledge, this is the first report on tick-borne bacterial pathogens in ticks and rodents from the China-Vietnam border. These results expand the knowledge of the geographical distribution and vector diversity of tick-borne bacterial pathogens in China and are conducive to the evaluation of thee potential public health risk.

Prevalence of three important tick-borne pathogens in ticks and humans in Shaanxi Province, Northwest China

The investigation of important prevalent tick-borne pathogens is central to the control of tick-borne diseases. To understand the prevalence of Borrelia burgdorferi s.l., Borrelia miyamotoi, and the Alongshan virus in ticks and patients in Shaanxi Province, China, a total of 670 adult ticks and 524 patient blood samples were collected in the region between 2022 and 2023. In this study, PCR was used to estimate the prevalence of the three pathogens. The results revealed that the overall positive rates of B. burgdorferi s.l, B. miyamotoi, and ALSV infection in the collected ticks were 13.58 %, 2.46 %, and 4.17 %, respectively. Three genospecies of B. burgdorferi s.l. were detected in this study, namely, B. garinii, B. afzelii, and B. bavariensis, with positive rates of 4.63 %, 3.58 %, and 5.37 %, respectively. The prevalence rates of B. miyamotoi, ALSV  and B. burgdorferi s.l. in the patients were 0.38 %, 0.95 %, and 15 %, respectively. Moreover, B. burgdorferi s.l. and ALSV coinfection was also detected in three patients. Evolutionary analysis revealed that the isolate of B. miyamotoi belongs to the Asian type (Siberian type) and that of ALSV is closely related to that of Finland. To our knowledge, this is the first report on B. miyamotoi and ALSV detection in both ticks and humans in Shaanxi Province; the prevalence indicates that the regions in this province might be endemic areas. The results also suggest that humans in these regions are at risk of infection with these three tick-borne diseases.

Non-Chemical Control of Nymphal Longhorned Tick, Haemaphysalis longicornis Neumann 1901 (Acari: Ixodidae), Using Diatomaceous Earth

The longhorned tick (LHT), Haemaphysalis longicornis Neumann (Acari: Ixodidae), is a serious invasive pest in North America where its geographical range is expanding with high densities associated with commercial animal production. There are only a few chemical pesticides available for LHT control, which can lead to the evolution of resistant strains. Diatomaceous earth (DE) was shown to be effective in killing some important tick species but was not examined for LHTs. When LHT nymphs were dipped for about 2-4 s into DE, transferred to Petri dishes (one tick/dish), and incubated at 30 °C and 70% relative humidity, the median survival time was 4.5 h. A locomotor activity assay showed that there was no difference in the overall distance traveled between the DE-treated and control ticks except during the first 2 h after exposure. In a field-simulated study in which a dose of 5.0 g DE/m2 was applied to pine needle litter infested with LHT, all the LHTs were dead at 24 h with no control mortality. Scanning electron micrographs showed the mineral adhering to all surfaces of the tick. The results indicated that DE is effective in killing nymphal LHTs and could be an alternative to the use of chemical acaricides with the advantage of managing pesticide resistance through the killing by a different mode of action and could be used for organically certified animal husbandry.

Molecular Identification of Borrelia spp. from Ticks in Pastures Nearby Livestock Farms in Korea

Simple Summary

Lyme borreliosis is caused by a spirochete from the Borrelia burgdorferi sensu lato group. Borrelia afzelii and B. garinii are known to be pathogenic to humans. The main vector for Lyme borreliosis is the Ixodes tick. In this study, Borrelia infection was confirmed in Ixodes,Haemaphysalis, and Amblyomma ticks. To our knowledge Borrelia infection was first confirmed in Amblyomma testudinarium in Korea. Based on phylogenetic analysis, all sequences were aligned with B. afzelii isolates and showed a close relationship with high identity. Considering that B. afzelii causes infectious zoonotic diseases, continuous monitoring and attention are still required (although a low prevalence was recorded in this study).

Abstract

Ticks are vectors that spread pathogenic bacteria, viruses, and protozoa. As the number of ticks increases due to climate change, the importance of the study of tick-borne pathogens has also increased. This study was conducted to investigate the distribution of the major tick species causing Lyme borreliosis and regional differences in the prevalence of Borrelia spp. by tick species. Borrelia infection was confirmed not only in Ixodes ticks, which are the major vectors of Borrelia spp., but also in Haemaphysalis and Amblyomma ticks. PCR targeting the 5S-23S rRNA intergenic spacer region (rrf-rrl) was performed to confirm Borrelia positivity. A total of 6102 ticks (736 pools) were tested, and the proportion was Haemaphysalis longicornis nymphs and adults at 69.2%, Haemaphysalis flava nymphs and adults at 13.9%, Haemaphysalis spp. larva at 14.3%, Ixodes nipponensis at 0.8%, and Amblyomma testudinarium at 1.9%. Ixodes nipponensis showed the highest minimum infection rate (MIR: 34.00; 17 pools/50 ticks) for Borrelia spp., followed by A. testudinarium (MIR: 0.88), and H. longicornis (MIR: 0.05). In particular, to our knowledge Borrelia infection was first confirmed in A. testudinarium in Korea. As a result of phylogenetic analysis, all sequences were grouped with Borreliaafzelii isolates and showed a close relationship with high identity. Considering that B. afzelii causes infectious zoonotic diseases, continuous monitoring and attention are needed, although it has a low prevalence in this study.

Mapping ticks and tick-borne pathogens in China

Understanding ecological niches of major tick species and prevalent tick-borne pathogens is crucial for efficient surveillance and control of tick-borne diseases. Here we provide an up-to-date review on the spatial distributions of ticks and tick-borne pathogens in China. We map at the county level 124 tick species, 103 tick-borne agents, and human cases infected with 29 species (subspecies) of tick-borne pathogens that were reported in China during 1950-2018. Haemaphysalis longicornis is found to harbor the highest variety of tick-borne agents, followed by Ixodes persulcatus, Dermacentor nutalli and Rhipicephalus microplus. Using a machine learning algorithm, we assess ecoclimatic and socioenvironmental drivers for the distributions of 19 predominant vector ticks and two tick-borne pathogens associated with the highest disease burden. The model-predicted suitable habitats for the 19 tick species are 14‒476% larger in size than the geographic areas where these species were detected, indicating severe under-detection. Tick species harboring pathogens of imminent threats to public health should be prioritized for more active field surveillance.

The Unexpected Holiday Souvenir: The Public Health Risk to UK Travellers from Ticks Acquired Overseas

Overseas travel to regions where ticks are found can increase travellers' exposure to ticks and pathogens that may be unfamiliar to medical professionals in their home countries. Previous studies have detailed non-native tick species removed from recently returned travellers, occasionally leading to travel-associated human cases of exotic tick-borne disease. There are 20 species of tick endemic to the UK, yet UK travellers can be exposed to many other non-native species whilst overseas. Here, we report ticks received by Public Health England's Tick Surveillance Scheme from humans with recent travel history between January 2006 and December 2018. Altogether, 16 tick species were received from people who had recently travelled overseas. Confirmed imports (acquired outside of the UK) were received from people who recently travelled to 22 countries. Possible imports (acquired abroad or within the UK) were received from people who had recently travelled to eight European countries. Species-specific literature reviews highlighted nine of the sixteen tick species are known to vector at least one tick-borne pathogen to humans in the country of acquisition, suggesting travellers exposed to ticks may be at risk of being bitten by a species that is a known vector, with implications for novel tick-borne disease transmission to travellers.

Vector competence studies with hard ticks and Borrelia burgdorferi sensu lato spirochetes: A review

Use of emerging technology allowing for identification of genetic material from pathogens and endosymbionts in ticks collected from humans, domestic animals, wildlife, or the environment has resulted in an avalanche of new data on tick-microorganism associations. This rapidly growing stream of new information is a tremendous resource but also presents challenges, including how detection of pathogen genetic material in ticks should best be interpreted. There is a tendency in the more recent published literature to incorrectly use the term “vector” based on detection of pathogen genetic material from tick species not experimentally confirmed to serve as vectors of the pathogen in question. To serve as a vector of a horizontally maintained pathogen, such as a Borrelia burgdorferi sensu lato (s.l.) Lyme borreliosis spirochete, the tick species in question must be capable of acquiring the pathogen while feeding in the larval or nymphal stage on an infectious host, maintaining it transstadially through the molt, and then transmitting the pathogen to a naïve host while feeding in the subsequent nymphal or adult stage. This review examines the experimental evidence for and against species of hard (ixodid) ticks from different genera to serve as vectors of B. burgdorferi s.l. spirochetes. Of the 18 Ixodes species ticks evaluated to date, 13 were experimentally confirmed as vectors of B. burgdorferi s.l. spirochetes. These studies focused primarily on the three major Lyme borreliosis agents: Borrelia burgdorferi sensu stricto, Borrelia afzelii, and Borrelia garinii. In striking contrast, none of 8 tick species from other genera (1 Amblyomma species, 5 Dermacentor species, and 2 Haemaphysalis species) evaluated to date were unequivocally experimentally confirmed as vectors of B. burgdorferi s.l. spirochetes. The strength of the evidence for or against each tick species to serve as a vector of B. burgdorferi s.l. spirochetes is discussed together with key knowledge gaps and research challenges.

A molecular survey of Anaplasma, Ehrlichia, Bartonella and Theileria in ticks collected from southeastern China

To investigate the prevalence of Anaplasma, Ehrlichia, Bartonella and Theileria, we collected ticks from small mammals in six counties of Zhejiang Province in southeastern China. Polymerase chain reaction (PCR) amplification was performed to test Anaplasma, Ehrlichia, Bartonella and Theileria in tick samples. Positive PCR products were sequenced and then compared with previously published sequences deposited in GenBank using BLAST. About 292 adult ticks were captured and the dominant tick species were Ixodes sinensis and Haemaphysalis longicornis. Overall, 34 ticks (11.6%) were tested positive for at least one pathogen of Anaplasma, Ehrlichia, Bartonella and Theileria. Rates of PCR-positivity to Anaplasma, Ehrlichia, Bartonella and Theileria were 5.5, 1.7, 2.4 and 2.4%, respectively. Positive rates of Anaplasma, Bartonella and Theileria were significantly different among ticks of different species. Prevalence of Anaplasma and Theileria varied significantly among ticks of different counties. Anaplasma, Ehrlichia, Bartonella and Theileria were widely prevalent in ticks in Zhejiang Province suggesting other tick-borne pathogens should also be suspected if patients had history of tick bites.

Prevalence and Identification of Borrelia burgdorferi Sensu Lato Genospecies in Ticks from Northeastern China

Lyme disease is considered as one of important tick-transmitted zoonosis in northeastern China, where the causative agents, the Borrelia burgdorferi sensu lato (s.l.) complex, remain poorly characterized. The purpose of the present study was to determine the prevalence and genospecies of B. burgdorferi s.l. in ticks in northeastern China. In May, 2015, a total of 2785 unfed adult ticks were collected in the Jilin and Heilongjiang provinces of northeastern China, with the predominant tick species of Ixodes persulcatus (59.9%), followed by Haemaphysalis concinna (14.8%), Haemaphysalis longicornis (8.9%), Dermacentor nuttalli (9.4%), and Dermacentor silvarum (7.0%). Only I. persulcatus was tested positive for Borrelia spirochetes DNA by PCR, targeting the 5S-23S rRNA intergenic spacer and 16S rRNA genes, with a prevalence of 1.9%. Phylogenetic analysis based on the partial 5S-23S rRNA intergenic spacer and 16S rRNA genes showed that these positive samples were grouped into four pathogenic genospecies for humans, including Borrelia garinii (2.8%), Borrelia afzelii (0.2%), Borrelia bavariensis (0.1%), and Borrelia bissettii (0.1%). These results showed that B. garinii is the predominant genospecies and I. persulcatus is the main tick host and carrier in northeastern China. To our knowledge, B. bissettii were detected for the first time in China.

Potential Spatial Distribution of the Newly Introduced Long-horned Tick, Haemaphysalis longicornis in North America

The North American distributional potential of the recently invaded tick, Haemaphysalis longicornis, was estimated using occurrence data from its geographic range in other parts of the world and relevant climatic data sets. Several hundred candidate models were built using a correlative maximum entropy approach, and best-fitting models were selected based on statistical significance, predictive ability, and complexity. The median of the best-fitting models indicates a broad potential distribution for this species, but restricted to three sectors—the southeastern United States, the Pacific Northwest, and central and southern Mexico.

Discovery of Haemaphysalis longicornis (Ixodida: Ixodidae) Parasitizing a Sheep in New Jersey, United States

We report the discovery of large numbers of Haemaphysalis longicornis Neumann (Ixodida: Ixodidae) infesting a sheep in Hunterdon County, New Jersey, United States. All life stages were found on the sheep, which had no history of travel outside the country. H. longicornis is native to East Asia, and there are invasive populations in Australia, New Zealand and several Pacific islands, where this tick is a major livestock pest. It is currently unknown whether the New Jersey collections represent a limited or established population, but because this species could present a significant threat to human and animal health in the United States, vigilance is encouraged.

Molecular and morphological identification of a human biting tick, Amblyomma testudinarium (Acari: Ixodidae), in Taiwan

Genetic identity and morphological features of a human biting tick, Amblyomma testudinarium, were determined for the first time in Taiwan. Morphological features of adult male and female ticks of Am. testudinarium were observed and photographed by a stereo- microscope. The genetic identity was analyzed by comparing the sequences of mitochondrial 16S ribosomal DNA gene obtained from 18 strains of ticks representing 10 species of Amblyomma, and four outgroup species of Dermacentor and Rhipicephalus ticks. Nine major clades could be easily distinguished by neighbour-joining analysis and were congruent by maximum-parsimony method. All these Am. testudinarium ticks collected from Taiwan and Japan were genetically affiliated to a monophyletic group with highly homogeneous sequence (99.8-100% similarity), and can be discriminated from other species of Amblyomma and other genera of ticks (Dermacentor and Rhipicephalus) with a sequence divergence ranging from 6.9 to 23.9%. Moreover, intra- and inter-species analysis based on the genetic distance (GD) values indicated a lower level (GD < 0.003) within the same lineage of Am. testudinarium ticks collected from Taiwan and Japan, as compared with other lineage groups (GD > 0.108) of Amblyomma ticks, as well as outgroup (GD > 0.172) species. Our results provide the first distinguished features of adult Am. testudinarium ticks and the first genetic identification of Am. testudinarium ticks collected from humans in Taiwan. Seasonal prevalence, host range, and vectorial capacity of this tick species in Taiwan need to be further clarified.

Emerging tick-borne infections in mainland China: an increasing public health threat

Since the beginning of the 1980s, 33 emerging tick-borne agents have been identified in mainland China, including eight species of spotted fever group rickettsiae, seven species in the family Anaplasmataceae, six genospecies in the complex Borrelia burgdorferi sensu lato, 11 species of Babesia, and the virus causing severe fever with thrombocytopenia syndrome. In this Review we have mapped the geographical distributions of human cases of infection. 15 of the 33 emerging tick-borne agents have been reported to cause human disease, and their clinical characteristics have been described. The non-specific clinical manifestations caused by tick-borne pathogens present a major diagnostic challenge and most physicians are unfamiliar with the many tick-borne diseases that present with non-specific symptoms in the early stages of the illness. Advances in and application of modern molecular techniques should help with identification of emerging tick-borne pathogens and improve laboratory diagnosis of human infections. We expect that more novel tick-borne infections in ticks and animals will be identified and additional emerging tick-borne diseases in human beings will be discovered.