Rickettsial seropositivity in the indigenous community and animal farm workers, and vector surveillance in Peninsular Malaysia

Challenges for ticks and tick-borne diseases research in Southeast Asia: Insight from the first international symposium in Cambodia

BACKGROUND

Ticks, as critical vectors of a variety of pathogens, pose a significant public health challenge globally. In Southeast Asia (SEA), ticks are responsible for transmitting a diverse array of pathogens affecting humans and animals. The geographical and ecological diversity of SEA provides a unique environment that supports a wide range of tick species, which complicates the management and study of tick-borne diseases (TBDs).

METHODOLOGY/PRINCIPAL FINDINGS

This article synthesizes findings from the first international symposium on ticks and TBDs in Southeast Asia, held in Phnom Penh on June 22 and 23, 2023. It highlights regional efforts to understand tick ecology and pathogen transmission. This paper proposes to present a summary of the various presentations given during the symposium following 3 main parts. The first one is devoted to the state of knowledge regarding ticks and TBDs in SEA countries, with presentations from 6 different countries, namely Cambodia, Indonesia, Laos, Malaysia, Thailand, and Vietnam. The second part focuses on the development of new research approaches on tick-borne pathogens (TBPs) and TBDs. The last part is a summary of the round table discussion held on the final day, with the aim of defining the most important challenges and recommendations for researches on TBP and TBD in the SEA region.

CONCLUSIONS/SIGNIFICANCE

Key topics discussed include advancements in diagnostic tools, such as MALDI-TOF MS and proteomics, and the development of sustainable strategies for tick management and disease prevention. The symposium facilitated the exchange of knowledge and collaborative networks among experts from various disciplines, promoting a unified approach to tackling TBDs in the region. The symposium underscored the need for enhanced surveillance, diagnostics, and inter-regional cooperation to manage the threat of TBDs effectively. Recommendations include the establishment of a regional database for tick identification and the expansion of vector competence studies. These initiatives are crucial for developing targeted interventions and understanding the broader implications of climate change and urbanization on the prevalence of TBDs.

Molecular surveillance of microbial agents from cattle-attached and questing ticks from livestock agroecosystems of Antioquia, Colombia

Ticks are obligate ectoparasites and vectors of pathogens affecting health, agriculture, and animal welfare. This study collected ticks from the cattle and questing ticks of 24 Magdalena Medio Antioquia region cattle farms. Genomic DNA was extracted from the specimens (individual or pools) of the 2088 adult ticks collected from cattle and 4667 immature questing ticks collected from pastures. The molecular detection of Babesia, Anaplasma, Coxiella and Rickettsia genera was performed by polymerase chain reaction amplification and subsequent DNA sequencing. In a total of 6755 Rhipicephalus microplus DNA samples, Anaplasma marginale was the most detected with a frequency of 2% (Confidence Interval- CI 1.68-2.36), followed by Babesia bigemina with 0.28% (CI 0.16-0.44), Coxiella spp. with 0.15% (CI 0.07-0.27), and Rickettsia spp. with 0.13% (CI 0.06-0.25). Molecular analysis of the DNA sequences obtained from the tick samples revealed the presence of Coxiella-like endosymbiont and R. felis. These results demonstrated the diversity of microorganisms present in R. microplus ticks predominantly associated with cattle and questing ticks from livestock agroecosystems, suggesting their role as reservoirs and potential biological vectors of these microorganisms on the studied sites. Also, it emphasizes the need to combine acarological surveillance with clinical diagnoses and control strategies on regional and national levels.

Haemaphysalis wellingtoni (Acari: Ixodidae) from the helmeted guineafowl, Numida meleagris (Galliformes: Numididae): A new tick-host record in Peninsular Malaysia

This paper describes a new tick-host record of Haemaphysalis wellingtoni from the helmeted guineafowl (Numida meleagris) in Peninsular Malaysia. This record is also the first report of a tick infestation from N. meleagris in Asia. A checklist of the tick-guineafowl associations has been designed, resulting in 32 tick species including H. wellingtoni recorded as infesting N. meleagris worldwide. A list of pathogens harboured or transmitted by H. wellingtoni is provided. The status of H. wellingtoni as a true parasite of N. meleagris, and the health threat posed to the guineafowls are discussed in this paper.

Molecular Survey of Rickettsia raoultii in Ticks Infesting Livestock from Pakistan with Notes on Pathogen Distribution in Palearctic and Oriental Regions

Ticks are hematophagous ectoparasites that transmit different pathogens such as Rickettsia spp. to domestic and wild animals as well as humans. Genetic characterizations of Rickettsia spp. from different regions of Pakistan are mostly based on one or two genetic markers and are confined to small sampling areas and limited host ranges. Therefore, this study aimed to molecularly screen and genetically characterize Rickettsia spp. in various tick species infesting camels, sheep, and goats. All the collected tick specimens were morphologically identified, and randomly selected tick species (148) were screened molecularly for the detection of Rickettsia spp. by amplifying three rickettsial DNA fragments, namely, the citrate-synthase gene (gltA), outer-membrane protein A (ompA), and outer-membrane protein B (ompB). After examining 261 hosts, 161 (61.7%) hosts were found infested by 564 ticks, including 287 (50.9%) nymphs, 171 (30.3%) females, and 106 (18.8%) males in five districts (Kohat, Dera Ismail Khan, Lower Dir, Bajaur, and Mansehra). The highest occurrence was noted for Hyalomma dromedarii (number = 72, 12.8%), followed by Haemaphysalis sulcata (n = 70, 12.4%), Rhipicephalus turanicus (n = 64, 11.3%), Rhipicephalus microplus (n = 55, 9.7%), Haemaphysalis cornupunctata (n = 49, 8.7%), Hyalomma turanicum (n = 48, 8.5%), Hyalomma isaaci (n = 45, 8.0%), Haemaphysalis montgomeryi (n = 44, 7.8%), Hyalomma anatolicum (n = 42, 7.5%), Haemaphysalis bispinosa (n = 38, 6.7%), and Rhipicephalus haemaphysaloides (n = 37, 6.6%). A subset of 148 ticks were tested, in which eight (5.4%) ticks, including four Hy. turanicum, two Ha. cornupunctata, one Ha. montgomeryi, and one Ha. bispinosa, were found positive for Rickettsia sp. The gltA, ompA, and ompB sequences revealed 100% identity and were phylogenetically clustered with Rickettsia raoultii reported in China, Russia, USA, Turkey, Denmark, Austria, Italy, and France. Additionally, various reports on R. raoultii from Palearctic and Oriental regions were summarized in this study. To the best of our knowledge, this is the first report regarding genetic characterization and phylogenetic analysis of R. raoultii from Pakistan. Further studies to investigate the association between Rickettsia spp. and ticks should be encouraged to apprise effective management of zoonotic consequences.

Metagenomics of culture isolates and insect tissue illuminate the evolution of Wolbachia, Rickettsia and Bartonella symbionts in Ctenocephalides spp. fleas

While fleas are often perceived simply as a biting nuisance and a cause of allergic dermatitis, they represent important disease vectors worldwide, especially for bacterial zoonoses such as plague (transmitted by rodent fleas) and some of the rickettsioses and bartonelloses. The cosmopolitan cat (Ctenocephalides felis ) and dog (Ctenocephalides canis ) fleas, as well as Ctenocephalides orientis (restricted to tropical and subtropical Asia), breed in human dwellings and are vectors of cat-scratch fever (caused by Bartonella spp.) and Rickettsia spp., including Rickettsia felis (agent of flea-borne spotted fever) and Rickettsia asembonensis , a suspected pathogen. These Rickettsia spp. are members of a phylogenetic clade known as the ‘transitional group’, which includes both human pathogens and arthropod-specific endosymbionts. The relatively depauperate flea microbiome can also contain other endosymbionts, including a diverse range of Wolbachia strains. Here, we present circularized genome assemblies for two C. orientis -derived pathogens (Bartonella clarridgeiae and R. asembonensis ) from Malaysia, a novel Wolbachia strain (w Cori), and the C. orientis mitochondrion; all were obtained by direct metagenomic sequencing of flea tissues. Moreover, we isolated two Wolbachia strains from Malaysian C. felis into tick cell culture and recovered circularized genome assemblies for both, one of which (w CfeF) is newly sequenced. We demonstrate that the three Wolbachia strains are representatives of different major clades (‘supergroups’), two of which appear to be flea-specific. These Wolbachia genomes exhibit unique combinations of features associated with reproductive parasitism or mutualism, including prophage WO, cytoplasmic incompatibility factors and the biotin operon of obligate intracellular microbes. The first circularized assembly for R. asembonensis includes a plasmid with a markedly different structure and gene content compared to the published plasmid; moreover, this novel plasmid was also detected in cat flea metagenomes from the USA. Analysis of loci under positive selection in the transitional group revealed genes involved in host–pathogen interactions that may facilitate host switching. Finally, the first B. clarridgeiae genome from Asia exhibited large-scale genome stability compared to isolates from other continents, except for SNPs in regions predicted to mediate interactions with the vertebrate host. These findings highlight the paucity of data on the genomic diversity of Ctenocephalides -associated bacteria and raise questions regarding how interactions between members of the flea microbiome might influence vector competence.

The dynamics of the microbiome in Ixodidae are shaped by tick ontogeny and pathogens in Sarawak, Malaysian Borneo

Tick-borne diseases have recently been considered a potential emerging public health threat in Malaysia; however, fundamental studies into tick-borne pathogens and microbiome appear limited. In this study, six tick species (Ixodes granulatus, Haemaphysalis hystricis, Haemaphysalis shimoga, Dermacentor compactus, Dermacentor steini and Dermacentor atrosignatus) collected from two primary forests and an oil palm plantation in Sarawak, Malaysian Borneo, were used for microbiome analysis targeting bacterial 16S rDNA using next-generation sequencing (NGS). In addition, bacterial species were further characterized in conventional PCRs to identify potential pathogens. Sequences generated from NGS were first filtered with the Decontam package in R before subsequent microbial diversity analyses. Alpha and beta analyses revealed that the genus Dermacentor had the highest microbial diversity, and H. shimoga significantly differed in microbial composition from other tick species. Alpha and beta diversities were also significantly different between developmental stages of H. shimoga. Furthermore, we observed that some bacterial groups were significantly more abundant in certain tick species and developmental stages of H. shimoga. We tested the relative abundances using pairwise linear discriminant analysis effect size (LEfSe), which also revealed significant microbial composition differences between Borrelia-positive and Borrelia-negative I. granulatus ticks. Finally, pathogenic and potentially pathogenic bacteria circulating in different tick species, such as Rickettsia heilongjiangensis, Ehrlichia sp., Anaplasma sp. and Bartonella spp. were characterized by PCR and sequencing. Moreover, Coxiella and Francisella-like potential symbionts were identified from H. shimoga and D. steini, respectively. More studies are required to unravel the factors associated with the variations observed in this study.

Advanced approaches for the diagnosis and chemoprevention of canine vector-borne pathogens and parasites-Implications for the Asia-Pacific region and beyond

Vector-borne pathogens (VBPs) of canines are a diverse range of infectious agents, including viruses, bacteria, protozoa and multicellular parasites, that are pernicious and potentially lethal to their hosts. Dogs across the globe are afflicted by canine VBPs, but the range of different ectoparasites and the VBPs that they transmit predominate in tropical regions. Countries within the Asia-Pacific have had limited prior research dedicated to exploring the epidemiology of canine VBPs, whilst the few studies that have been conducted show VBP prevalence to be high, with significant impacts on dog health. Moreover, such impacts are not restricted to dogs, as some canine VBPs are zoonotic. We reviewed the status of canine VBPs in the Asia-Pacific, with particular focus on nations in the tropics, whilst also investigating the history of VBP diagnosis and examining recent progress in the field, including advanced molecular methods, such as next-generation sequencing (NGS). These tools are rapidly changing the way parasites are detected and discovered, demonstrating a sensitivity equal to, or exceeding that of, conventional molecular diagnostics. We also provide a background to the armoury of chemopreventive products available for protecting dogs from VBP. Here, field-based research within high VBP pressure environments has underscored the importance of ectoparasiticide mode of action on their overall efficacy. The future of canine VBP diagnosis and prevention at a global level is also explored, highlighting how evolving portable sequencing technologies may permit diagnosis at point-of-care, whilst further research into chemopreventives will be essential if VBP transmission is to be effectively controlled.

Serological Evidence of Hepatitis E Virus (HEV) Infection Among Ruminant Farmworkers: A Retrospective Study from Malaysia

Background

As scant data are available about Hepatitis E virus (HEV) infection in Malaysia, this study aimed to determine the seroprevalence of HEV amongst ruminant farmworkers in Malaysia.

Methods

A total of 87 farmworkers provided serum samples, which were collected from eight farms. All serum samples were tested for anti-HEV IgG and anti-HEV IgM by an enzyme-linked immunosorbent assay (ELISA) using the Wantai HEV-IgG and HEV-IgM ELISA kits from Beijing Wantai Biological Pharmacy Enterprise Co., Ltd, Beijing, China.

Results

Farmworkers from six cattle farms, one sheep farm and one goat farm were investigated in this study. Only one farm practices zero-grazing, with the rest using rotational grazing. Of the 87 farmworkers, males comprised 83.9%, and almost half (47.1%) were aged 20-35 years old. By ethnic group, the vast majority were Malay. Most of the farmworkers have good hygiene practices; washing or changing their clothes and showering after dealing with farm animals were common. None of the farmworker serum samples had anti-HEV IgM and IgG detected (95% confidence interval (CI): 0, 0.0415).

Conclusion

The finding suggests that the farmworkers had no previous exposure to Hepatitis E, and were not at risk of occupational exposure to HEV infection. Our findings suggest that a zero seroprevalence of HEV infection among ruminant farmworkers in the Muslim majority country. Good farm management, hygiene practices and the absence of contact with swine-related contamination might have contributed to the no or minimal zoonotic risks of HEV amongst farmworkers surveyed in this study.

First report of Rickettsia asembonensis in small ruminants

Rickettsioses is a group of emerging infectious diseases in Southeast Asia caused by Gram-negative obligate intracellular bacteria in the Rickettsiae tribe. However, there is limited information regarding the vertebrate hosts of Rickettsia spp. in this region. This study aims to detect and identify Rickettsia agents present in wildlife and domesticated animals in Malaysia using Polymerase Chain Reaction (PCR) and sequencing of citrate synthase gene (gltA), followed by genotyping and phylogenetic analysis. Rickettsia sp. was detected in 2 (0.67%) of 300 wildlife and domesticated animal blood samples. The positive samples were derived from a goat (5.56% of 18) and a sheep (2.22% of 45). Both sequences demonstrated 99.64% sequence similarity to Rickettsia asembonensis, a species that is known to infect humans and macaques. This study reported for the first time the detection of R. asembonensis in sheep and goats in Malaysian farms, suggesting this species may be adapting to a wider range of animals, specifically farm animals. Therefore, this bacterium may pose a zoonotic threat to the local community particularly to the farmworkers or animal handlers. The low infection rate of this pathogen across different animals highlighted the need of continuous surveillance of emerging and reemerging pathogens among animal populations.

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

In this study, we investigated the presence of tick-borne pathogens in ticks removed from tick-bitten humans in the southwestern provinces of the Republic of Korea (ROK). We identified 33 ticks from three tick species, namely Amblyomma testudinarium (60.6%), Haemaphysalis longicornis (27.3%), and Ixodes nipponensis (12.1%) in order of occurrence via morphology and 16S rDNA-targeting polymerase chain reaction (PCR). Tick-borne pathogens were detected in 16 ticks using pathogen-specific PCR. From the results, 12 ticks (36.4%) tested positive for spotted fever group (SFG) Rickettsia: Rickettsia monacensis (1/12), R. tamurae (8/12), and Candidatus Rickettsia jingxinensis (3/12). Three ticks (9.1%) were positive for Anaplasma phagocytophilum. In addition, three ticks (9.1%) tested positive for Babesia gibsoni (1/3) and B. microti (2/3). In conclusion, we identified three tick species; the most common species was A. testudinarium, followed by H. longicornis and I. nipponensis. SFG Rickettsia, A. phagocytophilum, and Babesia spp. were the most frequently detected pathogens in ticks removed from tick-bitten humans. To our knowledge, this is the first report of R. tamurae and Ca. R. jingxinensis detection in Korea. The present results will contribute to the understanding of tick-borne infections in animals and humans in the ROK.

Current tools for the diagnosis and detection of spotted fever group Rickettsia

Spotted fever group (SFG) rickettsiae causes a number of diseases in humans worldwide, which can range from mild to highly lethal. Since the clinical presentations of rickettsioses caused by SFG rickettsiae are variable and may be similar to the diseases caused by other rickettsiae, such as Orientia tsutsugamushi (agent for scrub typhus), Coxiella burnetii (agent for Q fever) and the typhus group rickettsiae (agents for epidemic and murine typhus), the accurate diagnosis of infections caused by SFG Rickettsia remains challenging especially in resource-poor settings in developing countries. This review summarizes the various diagnostic and detection tools that are currently available for the confirmation of infections by SFG rickettsiae. The advantages and challenges pertaining to the different serological and molecular detections methods, as well as new assays in development, are discussed. The utility of the detection tools contributing to the surveillance of SFG rickettsiae in arthropods and animals are reviewed.

Seroprevalence of Rickettsial Infections in Northeast India: A Population-Based Cross-Sectional Survey

A cross-sectional survey was undertaken to estimate seroprevalence of immunoglobulin G antibodies against scrub typhus, spotted fever group rickettsiae, and typhus group rickettsiae in randomly selected 48 clusters in 12 districts of 3 Northeast states of India: Assam, Meghalaya, and Tripura. Individuals in 3 age groups (5-8, 9-17, and 18-45 years) were selected from each cluster. Sera (N = 2360) tested were collected as part of a national survey on dengue seroprevalence conducted between September 2017 and February 2018. Overall, seroprevalence of 2.5% was detected against rickettsioses, with highest positivity against spotted fever group rickettsiae, followed by scrub typhus and typhus group rickettsiae. Seroprevalence was highest in Tripura (3.7%), followed by Assam (2.6%) and Meghalaya (1.04%). Adults of 18 to 45 years of age were found to be most affected (3.8%). The study findings indicate the need for increasing testing facilities for active case detection at hospital levels. Efforts on implementing effective preventing strategies are suggested to be targeted in disease-specific endemic foci.

Occurrence of Anti-Rickettsia spp. Antibodies in Hospitalized Patients with Undifferentiated Febrile Illness in the Southern Region of Kazakhstan

Undifferentiated febrile illness still represents a demanding medical problem all over the world, but primarily in low- and middle-income countries. Scientific and clinical investigations related to undifferentiated febrile illness and rickettsial diseases in Kazakhstan are lacking. This study reflects the investigation of antibodies against spotted fever group (SFG) and typhus group (TG) rickettsiae in patients with undifferentiated febrile illness in the southern region of Kazakhstan (Almaty and Kyzylorda oblasts). Paired serum samples were gathered from 13 hospitals in these two oblasts and explored for the presence of IgM and IgG antibodies against typhus group and IgG antibodies against spotted fever group rickettsiae using ELISA. Patient's questionnaires were statistically analyzed. In total, 802 inpatients from Almaty (N = 9) and Kyzylorda (N = 4) hospitals were included in this research. Based on ELISA results, 250 patients out of 802 (31.2%) from both oblasts had IgG antibodies against SFG rickettsiae. Results from 11 (1.4%) patients indicated acute infection with tick-borne rickettsiosis. Regarding TG rickettsiae (R. typhi), a past infection was detected in 248 (30.9%) febrile patients and acute infection in 22 (2.7%) patients in the two selected oblasts. The data indicated that SFG and TG rickettsioses are present in Kazakhstan. Kazakh physicians should be aware of these emerging diseases in both investigated oblasts because the occurrence of these diseases is not suspected during day-to-day clinical practice. The identification of rickettsial pathogens and implementation of modern laboratory methods for the diagnostics of rickettsioses are in need throughout Kazakhstan.

Ticks and tick-borne pathogens in animals and humans in the island nations of Southeast Asia: A review

Ticks are blood-feeding ectoparasites and major vectors of pathogens that cause infectious diseases in humans and animals worldwide including mammals, birds and reptiles. Despite the growing scientific effort in the 20th century, there is still limited information on ticks and tick-borne pathogens in Southeast Asia, especially concerning medical, veterinary, socioeconomic and agricultural aspects in the island nations. This review provides an overview of the current state of knowledge of ticks and their pathogens in the island nations of Southeast Asia and peninsular Malaysia. We aim to stimulate further research studies on ticks and tick-borne pathogens of human and veterinary importance in this geographical region.

An overview of rickettsiae in Southeast Asia: Vector-animal-human interface

Rickettsioses are emerging, and re-emerging diseases caused by obligate intracellular arthropod-borne bacteria that infect humans and animals worldwide. Various rickettsiae such as Orientia, Rickettsia, Anaplasma and Ehrlichia have been circulated in companion, domesticated and wild animals through bites of infected ticks, fleas, lice or mites. This review summarizes the infections of rickettsiae, including the newly discovered regional species Rickettsia thailandii, Candidatus Rickettsia sepangensis, Candidatus Rickettsia johorensis, Candidatus Rickettsia laoensis, Candidatus Rickettsia mahosotii, Candidatus Rickettsia khammouanensis, Candidatus Anaplasma pangolinii, and other novel genotypes in vectors, humans and animals in Southeast Asia. Issues on some unidentified rickettsiae that elicit immune responses and production of antibodies that are cross-reactive with the antigens used are discussed. Knowledge gaps which required attention are also identified in this review.

Bacterial communities in Haemaphysalis, Dermacentor and Amblyomma ticks collected from wild boar of an Orang Asli Community in Malaysia

Ticks are hematophagous vectors of arthropod-borne disease agents globally. In Malaysia, despite seroprevalence studies indicating the presence of tick-borne diseases among the indigenous people, the etiological agents of these diseases are still unclear. These indigenous people, also known as the Orang Asli, still live in forested areas with frequent contact with wildlife. Wild boar are ubiquitously found in the forested areas where the Orang Asli communities are located and are commonly hunted as a food supplement. In this study, we aim to determine the tick species parasitizing wild boar from an Orang Asli community, and explore the tick-associated bacterial communities using 16 s rRNA amplicon sequencing on the Ion Torrent PGM™ platform. A total of 72 ticks were collected from three wild boar and were morphologically identified as Haemaphysalis hystricis (n = 32), Dermacentor compactus (n = 15), Amblyomma testudinarium (n = 13), Dermacentor steini (n = 10) and Dermacentor atrosignatus (n = 2). Across all tick samples, 910 bacterial taxa were identified. Although the bacterial communities were not significantly distinct between tick species in beta-diversity analyses, Coxiella, Rickettsia and Francisella were detected at high relative abundance in H. hystricis, D. compactus and D. steini respectively. Many other bacterial genera, including those that have been described in many different tick species, were also identified, including Pseudomonas, Acinetobacter, Staphylococcus and Corynebacterium. Beta-diversity analyses also showed that the bacterial communities were separated based on the animal host from which the ticks were collected from, suggesting that the bacterial communities here may be influenced by the animal skin microflora, host blood or the environment. PCR screening confirmed the presence of Rickettsia sp. related to spotted fever group Rickettsia in some of the ticks. This study provides baseline knowledge of the microbiome of H. hystricis, D. atrosignatus, D. compactus, D. steini and A. testudinarium parasitizing wild boar in this region. The information gained in this study provides the basis to target our efforts in H. hystricis, D. compactus and D. steini for the future investigation of vector competence and the zoonotic potential for the Coxiella, Rickettsia and Francisella detected here, as well as their implications for the risks of tick-borne diseases among the Orang Asli communities.

Distribution and Ecological Drivers of Spotted Fever Group Rickettsia in Asia

Spotted fever group and related rickettsia (SFGR) are a neglected group of pathogens that belong to the genus Rickettsia. SFGR are zoonotic and are transmitted by arthropod vectors, primarily ticks, fleas and mites to accidental hosts. These emerging and re-emerging infections are widely distributed throughout the world. Land-use change and increasing human-wildlife conflict compound the risk of SFGR infection to local people in endemic areas and travelers to these regions. In this article, we discuss the rickettsial organisms causing spotted fever and related diseases, their arthropod vectors in Asia and the impact of land-use change on their spread.

Assessment of a metabarcoding approach for the characterisation of vector-borne bacteria in canines from Bangkok, Thailand

BACKGROUND

Globally, bacterial vector-borne disease (VBD) exerts a large toll on dogs in terms of morbidity and mortality but nowhere is this more pronounced than in the tropics. Tropical environments permit a burgeoning diversity and abundance of ectoparasites some of which can transmit an extensive range of infectious agents, including bacteria, amongst others. Although some of these vector-borne bacteria are responsible for both animal and human diseases in the tropics, there is a scarcity of epidemiological investigation into these pathogens' prevalence. The situation is further exacerbated by frequent canine co-infection, complicating symptomatology that regular diagnostic techniques may miss or be unable to fully characterise. Such limitations draw attention to the need to develop screening tools capable of detecting a wide range of pathogens from a host simultaneously.

RESULTS

Here, we detail the employment of a next-generation sequencing (NGS) metabarcoding methodology to screen for the spectrum of bacterial VBD that are infecting semi-domesticated dogs across temple communities in Bangkok, Thailand. Our NGS detection protocol was able to find high levels of Ehrlichia canis, Mycoplasma haemocanis and Anaplasma platys infection rates as well as less common pathogens, such as "Candidatus Mycoplasma haematoparvum", Mycoplasma turicensis and Bartonella spp. We also compared our high-throughput approach to conventional endpoint PCR methods, demonstrating an improved detection ability for some bacterial infections, such as A. platys but a reduced ability to detect Rickettsia.

CONCLUSIONS

Our methodology demonstrated great strength at detecting coinfections of vector-borne bacteria and rare pathogens that are seldom screened for in canines in the tropics, highlighting its advantages over traditional diagnostics to better characterise bacterial pathogens in environments where there is a dearth of research.

Diversity of Rickettsiae in Feeding and Questing Ticks Collected From a Malaysian Forest Reserve Area

High seropositivity to Rickettsia conorii and Rickettsia felis has been reported in Malaysian indigenous community living in settlements adjacent to forest areas. The current study was conducted to determine the type and distribution of rickettsiae in feeding and questing ticks that were collected from a forest reserve area at Kuala Lompat in Pahang, Malaysia. Using PCR assays targeting citrate synthase (gltA), outer membrane protein A (ompA) and B (ompB) genes, rickettsiae were detected from approximately one-third of 98 ticks (mainly Dermacentor and Haemaphysalis spp.) collected from the forest reserve. BLAST analysis reveals the predominance of Rickettsia sp. RF2125 in both feeding and questing ticks and Rickettsia sp. TCM1 in the questing ticks. Sequences exhibiting close genetic relationship with Rickettsia raoultii, Rickettsia tamurae, Rickettsia heilongjiangensis, and Rickettsia asiatica were also detected from the ticks. This study highlights the diversity of rickettsial species and potential tick vectors which may contribute to the high seropositivity observed among the local communities.

Identification of Rickettsial Infections (Rickettsia sp. TH2014) in Ctenocephalides orientis Fleas (Siphonaptera: Pulicidae)

Rickettsia felis (Rickettsiales: Rickettsiaceae) is an emergent human pathogen that causes febrile illnesses in various parts of the world. This study describes the identification and growth characteristics of a R. felis-like organism (designated as Rickettsia sp. TH2014) cultured from Ctenocephalides orientis fleas in rural Malaysia. In this study, culturing of rickettsiae from filtered triturated flea lysates was performed in Aedes albopictus C6/36 cells. Cytopathic effects were observed from one of the samples 4 d post-inoculation. Electron microscopy revealed actively replicating intracytosolic coccobacillary organisms in the rickettsia-infected cells. Sequence analysis of amplified citrate synthase (gltA) gene fragment shows complete match of the rickettsia with Rickettsia sp. Rf31 in Southeast Asia, and 'Candidatus Rickettsia senegalensis' strain PU01-02 in Africa. The whole-genome sequence of Rickettsia sp. TH2014 was determined and assembled. The estimated genome size and guanine + cytosine content of the rickettsia are 1.37 Mb and 32.9%, respectively. The high values of average nucleotide identity and tetra-nucleotide signature correlation index obtained from pairwise genome comparison study suggest the identification of the rickettsia as R. felis. The whole-genome single-nucleotide polymorphism analysis demonstrates close genetic relatedness of the rickettsia with R. felis and Rickettsia asemboensis. However, based on sequence analyses of rickettsial genes (16S rDNA, gltA, ompB, and sca4), Rickettsia sp. TH2014 is found to be distinct from R. felis and R. asemboensis. The sequence analyses reveal that Rickettsia sp. TH2014 is highly similar to 'Ca. Rickettsia senegalensis' detected in fleas from Africa, Asia, and North America. Further investigation to provide insights on pathogenic potential and transmission dynamics of the rickettsia is warranted.

Worldwide Presence and Features of Flea-Borne Rickettsia asembonensis

Rickettsia asembonensis, the most well-characterized rickettsia of the Rickettsia felis-like organisms (RFLO), is relatively unknown within the vector-borne diseases research community. The agent was initially identified in peri-domestic fleas from Asembo, Kenya in an area in which R. felis was associated with fever patients. Local fleas collected from domestic animals and within homes were predominately infected with R. asembonensis with < 10% infected with R. felis. Since the identification of R. asembonensis in Kenya, it has been reported in other locations within Africa, Asia, the Middle East, Europe, North America, and South America. With the description of R. asembonensis-like genotypes across the globe, a need exists to isolate these R. asembonensis genotypes in cell culture, conduct microscopic, and biological analysis, as well as whole genome sequencing to ascertain whether they are the same species. Additionally, interest has been building on the potential of R. asembonensis in infecting vertebrate hosts including humans, non-human primates, dogs, and other animals. The current knowledge of the presence, prevalence, and distribution of R. asembonensis worldwide, as well as its arthropod hosts and potential as a pathogen are discussed in this manuscript.

Ehrlichia and Anaplasma Infections: Serological Evidence and Tick Surveillance in Peninsular Malaysia

Little information is available on human anaplasmosis and ehrlichiosis in Southeast Asia despite increasing reports of the detection of Anaplasma spp. and Ehrlichia spp. in the ticks. We report herein the serological findings against the tick-borne pathogens in a group of animal farm workers (n = 87) and indigenous people (n = 102) in Peninsular Malaysia. IgG antibodies against Ehrlichia chaffeensis were detected from 29.9% and 34.3% of farm workers and indigenous people, respectively, using commercial indirect immunofluorescence assays. Comparatively, only 6.9% of the indigenous people but none of the animal farm workers were seropositive to Anaplasma phagocytophilum. A polymerase chain reaction (PCR) assay targeting the 16S rRNA gene of Anaplasmataceae was used to identify Anaplastamataceae in ticks collected from various locations adjacent to the areas where the serological survey was conducted. In this study, a total of 61.5% of ticks infesting farm animals, 37.5% of ticks infesting peri-domestic animals in rural villages, 27.3% of ticks collected from wildlife animals, and 29.1% of questing ticks collected from forest vegetation were positive for Anaplasmataceae DNA. Sequence analyses of 16S rRNA gene region (238 bp) provide the identification for Anaplasma marginale, Anaplasma bovis, Anaplasma platys, A. phagocytophilum, and Anaplasma spp. closely related to Candidatus Cryptoplasma californiense in ticks. E. chaffeensis DNA was not detected from any ticks, instead, Ehrlichia sp. strain EBm52, Ehrlichia mineirensis and Candidatus Ehrlichia shimanensis are the only Ehrlichia sp. identified from cattle ticks in this study. Further investigation is required to ascertain the occurrence of zoonotic transmission of Ehrlichia and Anaplasma infections in Peninsular Malaysia.