Scanning electron microscopy as a confirmatory tool for morphological identification of Dirofilaria (Nochtiella) repens

Abstract

Background: Dirofilaria repens (Railliet & Henry, 1911) is a filarial nematode that mainly affects canids. It can also infect humans accidentally, causing subcutaneous or conjunctival lesions, especially in the Old-World, including Egypt. Scanning electron microscopy (SEM) is very useful in diagnosis and identification of different parasites including D. repens. Objective: The current work aimed use SEM as a confirmatory tool for morphological identification of D. repens. Material and Methods: Morphological diagnosis of the excised nematodes was performed by studying their naked eye and light microscopic appearance. This was then confirmed using scanning electron microscopy (SEM). Results: Three worms were identified; one excised from maxillofacial subcutaneous lesion and two were excised from the bulbar conjunctival lesion. All worms were females. Scanning electron microscopic examination showed external cuticular longitudinal ridges and circular striations on the whole worm length surface especially in the mid-body region, which are characteristic for D. repens. The anterior end of the worms was wider than the posterior end that possessed a dimple-like anal orifice. The anterior end of the subconjunctival worms was spoon-like, and wider than that of the subcutaneous worm. The dimple-like anal orifice of the subconjunctival worm was more retracted than that of the subcutaneous worm. Conclusion: Two new human cases of dirofilariasis have been diagnosed in Egypt. SEM was used as a confirmatory tool for their diagnosis.