The research team, led by Huan Li and Lei Ma of Hebei Normal University together with Jing Huang of Hebei Children’s Hospital, assembled an unusually large sample set for this kind of survey: 2,448 human fecal specimens and 215 ticks of the species Haemaphysalis longicornis, an aggressive, wide-ranging biting tick common across East Asia. Using polymerase chain reaction assays designed to amplify the 18S rRNA gene, a standard molecular marker for identifying eukaryotic microorganisms, the researchers screened every sample for Colpodella DNA. The 18S rRNA gene is favored in studies of protist diversity because it is present in all eukaryotes, contains both conserved and variable regions, and allows newly recovered sequences to be compared against a deep archive of reference sequences from known organisms.

The results were striking in their consistency across the two very different sample types. Colpodella DNA was detected in 136 of the human fecal samples, a detection rate of 5.56 percent, and in 11 of the tick samples, a rate of 5.12 percent. The near-identical prevalence in feces and ticks is one of the more intriguing aspects of the study, hinting at some shared route of exposure or a common environmental reservoir linking the human and tick samples, though the design of the study cannot distinguish among the many possible explanations, including ingestion of contaminated food or water, environmental pass-through, or a genuine biological association with the tick vector.

Every PCR-positive sample yielded a high-quality 18S rRNA sequence when the amplified DNA was read by Sanger sequencing, a validation step that strengthens confidence in the specificity of the detection. Because some of the tick-derived sequences were identical to one another, the researchers collapsed the data into representative sequence types, ultimately selecting one tick-derived sequence and 21 distinct human-derived sequence types for deeper analysis. These 22 representative sequences were deposited in GenBank under accession numbers QB017305 through QB017326, making them available to other researchers for comparison and future surveillance work.

Phylogenetic analysis, the technique biologists use to place newly recovered gene sequences on the tree of life, showed that all 22 representative sequences from the study clustered within previously reported Colpodella lineages. In other words, the DNA found in human stool and ticks belongs to the same evolutionary neighborhood as Colpodella species that have been described from aquatic and terrestrial habitats around the world. The sequences did not branch off into entirely novel territory, which suggests that the organisms detected in Hebei are related to known forms rather than representing a radically divergent new lineage, although species-level identification in this group remains difficult because morphology and molecular data do not always align neatly.

To probe the genetic variation within their dataset, the team performed a haplotype analysis, a method that groups sequences by their shared sets of variable sites. Among the analyzed sequences, they identified three haplotypes, indicating a modest but real degree of genetic diversity among the Colpodella organisms whose DNA was recovered from the samples. Haplotype networks and diversity statistics are standard tools in population genetics, and applying them to environmental protist DNA can reveal whether a detection reflects a single widespread genotype or a mixture of related strains circulating in the environment. In this case, the limited number of haplotypes suggests relatively constrained diversity in the sampled region, though the authors caution that broader sampling would be needed to draw firmer conclusions.

Understanding why this matters requires a short detour into evolutionary biology. Colpodella species are predatory flagellates that feed by a process called myzocytosis, in which they attach to another microbe, puncture its membrane, and suck out its cytoplasmic contents. This dramatic feeding strategy has fascinated cell biologists in part because it may resemble the evolutionary steps that gave rise to intracellular parasitism. Colpodellids are considered the free-living sister group to the Apicomplexa, the phylum that includes Plasmodium, the malaria parasite, and Toxoplasma gondii. Studying Colpodella therefore offers a window into how some of humanity’s most burdensome parasites may have evolved from free-living ancestors that once hunted their prey from the outside.

The new study also fits into a rapidly expanding literature on where Colpodella DNA shows up outside of ponds and soil. Recent surveys have reported the organism’s genetic traces in goats, foxes, and birds; in Hyalomma ticks infesting camels in Egypt; in ticks feeding on ruminants in Italy; in horses; in zoo animals; and even in the urine of a human patient. Clinically, isolated case reports have described Colpodella-like parasites in a woman in China and in a patient with neurological symptoms whose infection was linked to a potential novel tick-borne Colpodella species. A 2025 scoping review of the genus’s biological characteristics and zoonotic potential underscored how much remains unknown about whether these detections represent transient environmental exposure, colonization, or true infection.

That uncertainty is central to how the Hebei findings should be interpreted, and the authors are explicit about the limits of their method. PCR-based detection confirms only that Colpodella DNA was present in the sample; it cannot determine whether live organisms were present, whether they were actively replicating, whether they colonized the human gut or the tick, or whether they caused any disease. DNA can persist after an organism has died, and environmental contamination or passive passage through the body can both produce positive signals. Distinguishing among these possibilities will require complementary approaches, including attempts to culture the organisms, sequencing of additional genetic markers beyond the 18S rRNA gene, and biological studies of how Colpodella interacts with animal hosts.

Nevertheless, the study marks a meaningful addition to surveillance data on an understudied group of protists. The large number of human samples screened, the near-matching detection rates in feces and ticks, the successful sequencing of every positive sample, and the public deposition of 22 representative sequences collectively provide a foundation for future work. As molecular surveys continue to sweep ever more environments and host species, Colpodella keeps appearing in unexpected places, and each new detection sharpens the questions that make this genus scientifically compelling: how these predatory relatives of apicomplexan parasites move between environmental reservoirs, animals, and occasionally people, and whether any of them pose a genuine health risk. For now, the answer in Hebei Province is a well-documented molecular presence and a clear agenda for the research that must follow.

Subject of Research: Molecular detection and genetic diversity of Colpodella protist DNA in human fecal and tick samples in China

Article Title: Molecular Detection and Genetic Characterization of Colpodella spp. DNA in Human Fecal and Tick Samples from Hebei Province, China

Article References: Li, H., Huang, J., Zhang, M., Zhang, Y., Chen, Y., & Ma, L. (2026). Molecular Detection and Genetic Characterization of Colpodella spp. DNA in Human Fecal and Tick Samples from Hebei Province, China. Acta Parasitologica, 71(5), Article 234. https://doi.org/10.1007/s11686-026-01419-6

Image Credits: AI Generated

DOI: 10.1007/s11686-026-01419-6

Keywords: Colpodella, protists, Apicomplexa, Haemaphysalis longicornis, ticks, 18S rRNA, PCR detection, genetic diversity, haplotypes, Hebei Province, zoonotic potential, myzocytosis

Haemaphysalis longicornis, Neumann’s Asian longhorned tick, is widely regarded as one of the most invasive tick species in the world. Native to East Asia, it has demonstrated an extraordinary capacity for geographic expansion, most dramatically in the United States, where it was first detected in New Jersey in 2017 and has since spread across dozens of states. Unlike most tick species, females of H. longicornis can reproduce parthenogenetically, meaning a single fed female can found an entire population without ever mating. Combined with its broad host range, spanning birds, mammals, and occasionally humans, and its ability to transmit a suite of pathogens of veterinary and public health concern, including agents of theileriosis in cattle and severe fever with thrombocytopenia syndrome virus in humans, the species has earned its reputation as a serious biosecurity threat. Although H. longicornis had recently been reported from the Asian and European parts of Türkiye, georeferenced, verifiable evidence from the European continent remained conspicuously limited. The new study set out to close that gap with a rigorous, multi-method investigation.

The research team focused their fieldwork on the European side of Istanbul, a location of exceptional strategic importance for understanding tick dispersal into Europe. Istanbul sits astride a major migratory flyway linking Türkiye with northeastern and central Europe, and every spring and autumn millions of birds funnel through the region. Because birds are known to act as long-distance transport vehicles for ticks, capable of moving engorged larvae and nymphs hundreds or even thousands of kilometers in a matter of days, a ringing station in this bottleneck offered an ideal natural laboratory for detecting invasive tick incursions. During the 2025 spring and autumn migration seasons, the researchers examined birds captured at the ringing station for tick infestation. In addition to sampling avian hosts, the team collected questing ticks, host-seeking individuals that climb onto vegetation in wait of a passing host, from nearby habitats using the flagging technique, in which a cloth flag is dragged through grass and shrubs to snag feeding-stage ticks.

The scale of the sampling effort was substantial. Across the two migration seasons, a total of 4,816 birds representing the relevant host species were examined, yielding 108 Haemaphysalis specimens. Of these, 95 were identified as H. longicornis larvae and 6 as H. longicornis nymphs, with the remaining 7 specimens identified as the native species Haemaphysalis punctata nymphs. Crucially, no adult Haemaphysalis ticks were found on any of the birds examined, a pattern consistent with the known biology of the genus: immature stages, particularly larvae, are the life stages most commonly transported by birds. Ticks were recovered from 46 individual birds representing 17 host species. Remarkably, every avian host species from which H. longicornis was detected constituted a novel host association for the parasite, meaning these particular bird species had never before been documented as carriers of this invasive tick. Four of the six engorged larvae collected during the study moultered successfully to the nymphal stage under laboratory conditions, demonstrating that ticks transported by birds into the region remain viable and capable of continuing their development.

Species identification in tick research cannot rely on morphology alone, particularly for larval specimens, which are minute and morphologically conservative. The researchers therefore confirmed their identifications using molecular analysis based on the mitochondrial cytochrome c oxidase subunit I gene, or COI, a widely used DNA barcoding marker. COI sequence data generated from pooled Haemaphysalis samples were consistent with morphological identification as H. longicornis, and representative sequences clustered securely within the H. longicornis clade in phylogenetic analysis, leaving no ambiguity about the species’ identity. Of particular significance, three questing nymphs collected by trial flagging from vegetation proved morphologically indistinguishable from the COI-confirmed H. longicornis nymphs recovered from birds. The detection of host-seeking ticks in the environment is arguably the most consequential finding of the study, because questing ticks are, by definition, off the host and living independently in the local habitat. Their presence strongly suggests that H. longicornis is not simply a transient traveler through the region but may have established a self-sustaining local population on the European side of Istanbul.

The seasonal patterns uncovered by the study add an intriguing ecological dimension. When pooled across all host species, tick prevalence was higher in autumn than in spring, although the unadjusted comparison between seasons did not reach statistical significance. The team took a more sophisticated analytical approach, employing Fisher’s exact test, a two-sample test for the equality of proportions, and binomial generalized linear models that accounted for differences among host species. Once host species composition was properly controlled for in the model framework, autumn showed higher estimated odds of infestation than spring. This statistical nuance matters because raw prevalence figures can be misleading when different bird species, which vary widely in their propensity to carry ticks, are caught in different numbers at different times of year. By modeling the probability of infestation while holding host identity in the analysis, the researchers could extract a cleaner signal of seasonality, pointing toward autumn as the period of greatest tick movement through the flyway, possibly reflecting the activity rhythms of locally breeding tick populations.

The epidemiological stakes of this work are difficult to overstate. H. longicornis is a proven vector of multiple disease agents, and its parthenogenetic reproduction gives it an invasive capacity that most ticks lack. In regions where it has established, such as the eastern United States, the tick has been responsible for devastating infestations of livestock, including fatal blood loss in cattle, and has triggered intensive surveillance programs by agricultural and public health authorities. The tick’s tolerance of a broad range of climatic conditions suggests that much of Europe offers suitable habitat, and the presence of a reproductive population at the entrance to a major European flyway raises the prospect of rapid continental spread, with birds acting as a dispersal mechanism to deposit engorged larvae and nymphs across the landscapes of southeastern, central, and northeastern Europe. The Istanbul region, with its dense human population, abundant livestock in surrounding areas, and heavy bird traffic, represents an ideal staging ground for such an expansion.

The authors are careful to frame their conclusions in terms of what the evidence directly supports. The combination of ticks on multiple avian hosts and questing ticks recovered from the local environment indicates both transport and potential local establishment, but the precise extent of the established population, its origin, and its population genetic structure remain open questions. Whether the Turkish population arrived via birds from Asia, via domestic animals or trade, or through some combination of routes cannot yet be resolved from the present data. Ongoing surveillance at bird ringing stations along the flyway, together with broader environmental sampling across the European side of Istanbul and beyond, will be needed to map the true distribution and trajectory of the invasion. The researchers also emphasize the value of their methodology as a template: integrating routine bird ringing with tick collection, morphological identification, DNA barcoding, and statistically sound analysis of host effects provides a scalable model for detecting invasive ticks early, when management interventions are still feasible.

For public health authorities across Europe, the study serves as an urgent wake-up call. The European continent already contends with a growing burden of tick-borne diseases, including Lyme borreliosis and tick-borne encephalitis, transmitted by native species such as Ixodes ricinus. The arrival of an additional, highly invasive, parthenogenetic vector with an enormous host range compounds an already complex epidemiological landscape. Clinicians and veterinarians in the region may need to become familiar with H. longicornis, a morphologically distinctive tick whose presence could alter transmission dynamics for a range of pathogens. Equally, the study underscores the ecological importance of wild birds, which have often been underappreciated in invasive species risk assessments focused on trade, travel, and domestic livestock. The migratory corridors that connect Africa, the Middle East, Türkiye, and Europe function not only as conduits for avian biodiversity but, as this research demonstrates, as highways for their parasites.

What emerges from the Istanbul fieldwork is a clear and sobering picture: the Asian longhorned tick has crossed a biogeographic threshold. Georeferenced, molecularly confirmed specimens of Haemaphysalis longicornis now exist on the European continent, carried there on multiple previously unknown bird host species and recovered, in the form of host-seeking nymphs, from the soil and vegetation of the European side of Istanbul. Whether the coming years will see the species spread into the Balkans, central Europe, or beyond remains to be determined, but the ingredients for continental colonization, a suitable climate, abundant hosts, parthenogenetic reproduction, and an efficient dispersal mechanism in the form of millions of migrating birds, are all now assembled at Europe’s doorstep. The study, funded by the University of California, Los Angeles, and conducted by researchers spanning institutions in Türkiye and the United States, including Koc University Isbank Center for Infectious Diseases, Istanbul University-Cerrahpasa, Ondokuz Mayis University, Tekirdag Namik Kemal University, UCLA, and the USDA Agricultural Research Service, stands as both a warning and a call to action. Surveillance of birds, livestock, wildlife, and the environment along Europe’s migratory flyways will be essential in the years ahead, because as the new findings make clear, Europe’s next invasive tick may already be here, riding in on the wings of a songbird and waiting in the grass.