Molecular discovery of a unique Litomosoides lineage in the Gulf coast tick Amblyomma maculatum: First evidence of potential tick infection in North America.

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.