Molecular and morphological comparison of two different types of Habronema muscae (Nematoda: Habronematidae) in horse.

Habronema muscae is a spirurid nematode that undergoes developmental stages in the stomach of equids, causing chronic catarrhal gastritis. Despite preceding investigations have developed polymerase chain reaction (PCR)-based assays for molecular diagnosis, we aimed to assess the applicability of cytochrome c oxidase subunit 1 (cox1) sequences to identify the H. muscae infection and to assess the level of intraspecific variations in this parasite obtained from affected horses in Southern Iran. According to the morphological characterizations, two different isolates of H. muscae were identified. Although the majority of the recovered specimens had normal characterizations of H. muscae, a number of parasites showed an abnormal feature as large, asymmetrical, and thick cuticular extensions was observed at their anterior end (head region) in gross and histologic examinations. Unexpectedly, molecular assay disclosed that both morphologically distinct samples were completely identical to each other based on cox1 sequence. Multiple alignment of the cox1 amino acid sequences showed that all polymorphism sites were silent. Also, phylogenetic analysis provided strong support that H. muscae form a sister group to Spirocerca lupi and Thelazia callipaeda.