City Life Reshapes the Microbes Inside Thailand’s Brown Dog Ticks

The brown dog tick is one of the most successful parasites on the planet, quietly riding alongside domestic dogs into homes, kennels, and veterinary clinics on every inhabited continent. In Thailand, where the species Rhipicephalus linnaei thrives in both crowded city neighborhoods and remote rural villages, this arachnid does more than irritate pets. It can carry and transmit bacteria that sicken animals and people alike, making it a vector of genuine veterinary and public health concern. Now, a team of Thai and international researchers has mapped the invisible ecosystem living inside these ticks, and their findings reveal something striking: the microbial world within a tick looks dramatically different depending on where that tick calls home.

The study, published in the open-access journal Parasites & Vectors, was led by Artharee Rungrojn of the Mahidol Oxford Tropical Medicine Research Unit at Mahidol University in Bangkok, working with colleagues from Chulalongkorn University, Thailand’s Veterinary Research and Development Center, the French National Centre for Scientific Research, and the University of Oxford. The team collected 131 brown dog ticks from dogs across five Thai provinces, deliberately choosing sampling sites that spanned different geographical regions and contrasting ecological settings, from dense urban environments to rural landscapes. This design allowed them to ask a deceptively simple question with powerful implications: which forces, environmental or host-related, actually shape the community of bacteria that lives inside a tick?

To answer it, the researchers turned to a technology that has been transforming microbiome science. Rather than using conventional short-read sequencing, which reads only fragments of a gene and often leaves bacterial species ambiguously identified, they employed Oxford Nanopore Technology to sequence the full-length bacterial 16S rRNA gene. This gene, present in all bacteria, serves as a molecular barcode, and reading it in its entirety allows far more precise identification of which bacterial genera and species are present. For a vector like R. linnaei, where distinguishing a harmless symbiont from a dangerous pathogen matters enormously, that extra resolution is not a luxury but a necessity.

The headline finding concerns a single dominant organism. Candidatus Coxiella mudrowiae, a bacterium related to the genus that includes the agent of Q fever, was detected in every single tick examined. This kind of universal presence is the signature of a vertically transmitted symbiont, a microbe passed from mother to offspring through the generations rather than picked up from the environment. Such symbionts are increasingly recognized as essential partners in tick biology, often supplying vitamins and other nutrients that the tick’s blood-only diet lacks. The complete dominance of the R. linnaei microbiome by this one bacterium suggests a deep, ancient co-evolutionary relationship that persists regardless of where the ticks live.

Yet beneath that shared foundation, the researchers found substantial variation, and the drivers of that variation were unambiguous. Using a battery of statistical tools, including alpha diversity metrics that measure how many bacterial types are present, Bray-Curtis dissimilarities that quantify how different communities are from one another, principal coordinates analysis to visualize those differences, and PERMANOVA to test whether the patterns are statistically significant, the team showed that geography, habitat type, and blood-feeding status all left clear fingerprints on the tick microbiome. Ticks from different regions of Thailand harbored measurably different bacterial communities, and so did ticks from urban versus rural settings.

One of the most intriguing results concerns the urban-rural divide. Ticks collected in cities showed lower bacterial diversity than their rural counterparts. This pattern echoes findings from human microbiome research, where urban lifestyles and environments are repeatedly associated with reduced microbial diversity, but seeing the same signature in a tick population raises fascinating ecological questions. Urban ticks may encounter fewer environmental microbes, feed on dogs with different health and treatment profiles, or experience pressures such as acaricide exposure and habitat fragmentation that prune their microbial communities. Whatever the mechanism, the implication is that urbanization does not just change the landscape a tick inhabits; it changes the microscopic ecosystem the tick carries within it.

Blood-feeding status told a complementary story. Ticks that had engorged themselves with a blood meal showed altered microbial diversity compared with ticks that were still actively feeding or unfed. A blood meal is a transformative event in a tick’s life, triggering physiological changes, immune responses, and digestive activity, and the new data suggest it also reshuffles the bacterial residents of the tick’s body. This has direct relevance to disease transmission, because the ability of a tick to acquire, maintain, and pass on a pathogen, its so-called vector competence, is increasingly understood to depend on the microbial community that competes with or facilitates that pathogen. A feeding-induced shift in the microbiome could therefore influence whether a tick that picks up an infection while biting one host successfully transmits it to the next.

By contrast, the effects of tick sex and developmental stage were less pronounced, a somewhat surprising result given that these factors have been shown to matter in other tick species. The researchers also used ANCOM-BC2, a modern differential abundance method designed to handle the compositional quirks of microbiome data, to pinpoint specific bacterial taxa whose numbers rose or fell in association with ecological and host-related factors. Among the low-frequency taxa they detected were putative tick-associated pathogens, including species of Anaplasma and Ehrlichia, two genera of intracellular bacteria responsible for significant disease in dogs and, in some cases, in humans. Their detection at low frequency underscores both the value of sensitive full-length sequencing and the importance of continued surveillance in a region where tick-borne disease burden remains incompletely characterized.

The significance of this work extends beyond Thailand’s borders. R. linnaei belongs to the broader brown dog tick complex, a group of morphologically similar species whose taxonomy has only recently been untangled with molecular tools, and whose members transmit pathogens such as Rickettsia, Ehrlichia, and Babesia worldwide. Understanding what shapes the microbiome of this vector in Southeast Asia, a region of intense biodiversity, rapid urbanization, and close human-animal contact, provides a baseline for predicting how tick-borne disease risk might shift as landscapes change. If urban environments consistently simplify tick microbiomes, and if that simplification affects pathogen dynamics, then cities may be quietly engineering new patterns of disease risk that current surveillance systems are not designed to detect.

Methodologically, the study also makes a case that will resonate with microbiome researchers everywhere: full-length 16S rRNA sequencing on Nanopore platforms is a practical and powerful approach for vector microbiome investigations. The work emerged from Rungrojn’s doctoral research at Mahidol University and received support from the Wellcome Trust, MOTIP, and the Royal Society of Tropical Medicine and Hygiene, reflecting the growing international investment in understanding the hidden microbial dimensions of vector-borne disease. As sequencing technology becomes faster and cheaper, studies of this kind could move from snapshot surveys to longitudinal monitoring, tracking how tick microbiomes respond seasonally and as cities expand. For now, the message from Thailand’s dogs and their tiny passengers is clear: the microbes inside a tick are not a fixed inheritance but a living community, responsive to geography, habitat, and the simple act of taking a blood meal, and that responsiveness may hold keys to controlling the diseases these ticks spread.

Subject of Research: Environmental and host-associated factors shaping the bacterial microbiome of the brown dog tick Rhipicephalus linnaei in Thailand

Article Title: Environmental and host-associated determinants of microbiome variation in the brown dog tick Rhipicephalus linnaei in Thailand

Article References: Rungrojn, A., Chaisiri, K., Thaipadungpanit, J., Batty, E. M., Taweethavonsawat, P., Thempachana, O., Kongkaew, W., Morand, S., & Blacksell, S. D. (2026). Environmental and host-associated determinants of microbiome variation in the brown dog tick Rhipicephalus linnaei in Thailand. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07656-y

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07656-y

Keywords: Rhipicephalus linnaei, brown dog tick, microbiome, 16S rRNA, Oxford Nanopore sequencing, Candidatus Coxiella mudrowiae, Thailand, tick-borne pathogens, Anaplasma, Ehrlichia, urban ecology, vector competence