Survey of Ovine Nasal Bots (Oestrus ovis) and Associated Nasal Cavity Pathology in Sheep in Kogi State

Oestrosis caused by larvae of the nasal botfly Oestrus ovis is a widespread parasitic condition of sheep in the Guinea Savannah ecological zone of Nigeria's North Central geopolitical zone. This survey determined the prevalence of Oestrus ovis infestation and characterised associated gross and histopathological lesions of the nasal cavities in sheep slaughtered at Lokoja Abattoir, Kogi State, from March to August 2023. A total of 150 slaughtered sheep had their heads subjected to thorough anatomical dissection of the nasal passages and sinuses. Larvae recovered were identified by morphological examination and staged. Nasal mucosal samples were collected and processed histopathologically. The overall prevalence of Oestrus ovis was 34.0 percent, with mixed-stage infestations most common. Third-instar larvae were most frequently recovered. Gross lesions included mucopurulent nasal exudate, mucosal erosions, sinus congestion, and nasal turbinate destruction in heavy infestations. Microscopically, chronic rhinitis with transmural eosinophilic infiltration, goblet cell hyperplasia, and submucosal fibrosis were prominent. Severe infestations resulted in focal turbinate bone erosion visible on histology. These findings represent the first systematic documentation of Oestrus ovis pathology in Kogi State. Seasonal antiparasitic treatment with ivermectin during the fly season and improved sheep housing are recommended. Keywords: Oestrus ovis, oestrosis, sheep, nasal pathology, Kogi State