A nodular granulomatous posthitis caused by Halicephalobus sp. in a horse.

This report describes a case of nodular posthitis caused by Halicephalobus gingivalis in a 24-year-old warmblood horse. Macroscopic examination revealed a multinodular, partially ulcerated mass on the external lamina of the prepuce. Nematode migration from unfixed biopsy material in phosphate-buffered saline revealed adult nematodes with the typical morphological features of H. gingivalis: distinctive rhabditiform oesophagus with corpus, isthmus and bulb and the dorsoflexed ovary. The main histopathological features consisted of submucosal confluent granulomatous foci containing cross- and tangential sections of larval and adult nematodes surrounded by cellular debris, epitheloid macrophages, multinucleated giant cells, lymphocytes and plasma cells. Therapy including oral administration of moxidectin and local application of an ointment containing prednisolone and moxidectin was initiated but clinical response was poor. Five months later, the nodular mass was still present and histologically, the same lesions with numerous intact nematodes were identified. In the present case, a localized infection with granuloma formation in the area of the prepuce was observed. Clinically, it cannot be distinguished from other nematode infections or even from a squamous cell carcinoma. An accurate clinical examination followed by histopathological and parasitological examinations was necessary to establish the final diagnosis. This case is unusual in that the lesions were locally very extensive (10 cm), but they remained confined to the preputium and the nematodes did not spread haematogenously to other internal organs.