Ticks are well-known vectors of pathogens, including filarial nematodes, which can affect animal and human health. This review synthesizes current knowledge of filarial nematodes that utilize ticks as vectors, focusing on the Onchocercidae. Five genera of onchocercid filarial nematodes (Cercopithifilaria, Cherylia, Cruorifilaria, Monanema, and Yatesia) have demonstrated vector–parasite relationships with ticks, while Acanthocheilonema has only demonstrated molecular detection without confirmed vector competence. Vector competence has been experimentally proven for several species through documented development to infective stages. However, our understanding of tick-borne filarial nematodes remains limited owing to insufficient detection efforts and methodological challenges. Detection methods include traditional dissection, advanced imaging techniques such as microcomputed tomography (micro-CT), and molecular approaches, each with distinct advantages and limitations. To address knowledge gaps, future research should focus on conducting large-scale surveys of tick populations and wildlife to investigate vector competence, health impacts, and coinfection dynamics. Multi-disciplinary collaboration and community involvement in tick surveillance will advance our understanding of tick-borne filarial nematode ecology and epidemiology. Future research priorities include confirming vector competence where only molecular detection exists, investigating natural transmission patterns, and understanding the mechanisms influencing successful development in tick vectors. By addressing these knowledge gaps through systematic surveillance and experimental studies, we can better understand these complex host–parasite–vector relationships and their implications for animal health. Graphical Abstract

Tick‐borne filarial nematodes are a complex and understudied group of parasites that rely on ticks for transmission in vertebrates. This review examines how intrinsic and extrinsic factors may influence the successful transmission of filarial nematodes in tick vectors, drawing insights from extensively studied haematophagous dipteran vector systems. We explore how different tick life stages contribute to potential nematode transmission to the host and the influence of abiotic factors on nematode survival and development within ticks. Understanding nematode life stage periodicity and enhancement phenomena in tick‐borne filarial systems is equally important for determining transmission dynamics and co‐infection patterns. Also important to nematode transmission are vertebrate host movement and tick feeding patterns, which create opportunities for parasite exchange across ecological environments. Knowledge gaps include the physical and molecular mechanisms of transmission, the potential influence of tick genetic variation on vector competence, immune responses across different tick–filarial associations, and epidemiological studies of host and tick patterns of nematode infection. Comprehensive empirical data are also needed to model transmission patterns, including temperature and humidity thresholds for nematode development and survival, field‐based tick infection rates, and how tick immune responses affect these processes. Understanding these factors requires integrating expertise from multiple disciplines and adopting an ecosystem‐based perspective that considers the interconnected nature of vertebrate hosts, vectors, and environment in the transmission of filarial nematodes.

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Tick-transmitted filarioids are increasingly recognized globally, yet their diversity and transmission dynamics in North American ticks remain poorly characterized. We investigated the prevalence and genetic diversity of filarioids in Amblyomma maculatum (Gulf Coast tick), a vector of multiple pathogens in the United States. We screened 383 samples comprising 471 individual ticks collected from small mammals and vegetation between 2012 and 2016 from across Texas, using PCR assays targeting filarioid mitochondrial 12S rDNA and cox1 genes. The overall prevalence of filarioid DNA detection was 6.0%, with Litomosoides sp. the only filarioid worm detected. Host-associated ticks showed significantly higher detection rates than questing ticks (12.6% vs. 0.9%). Most positive samples were detected in ticks collected from Sigmodon hispidus (82.6%), a known natural vertebrate host for Litomosoides species in North America. Bayesian phylogenetic analyses of both genes revealed that all tick-derived Litomosoides sequences formed a strongly supported monophyletic clade sister to all known Litomosoides species, with 3.70-5.32% genetic divergence from the closest relative, L. sigmodontis, suggesting a previously uncharacterized lineage. Our study represents the first molecular detection of Litomosoides sp. in North American ixodid ticks, expanding the known diversity of tick-borne filarioids. Experimental studies are needed to establish whether A. maculatum supports complete parasite development and transmission of this unique Litomosoides lineage.