Veterinary Handbook Disease Finder

Nasal Bots


Other Names

  • Oestrus ovis



The sheep nasal bot fly deposits larvae in the nostrils of its host. Once deposited, the larvae will grow and can move within the nasal cavity and frontal sinuses causing irritation, resulting in sneezing and mucopurulent discharge from the nostrils. They can lead to debilitating secondary bacterial infections. Animals may attempt to avoid flies by running with their head down and nosing into corners. Infection is very common in Australian sheep and goats. Fly activity typically peaks around spring and late summer with warmer weather. However, this varies between regions.

Clinical Signs and Diagnosis

Infected sheep may not show any obvious clinical signs. Some sheep may be seen sneezing, snorting, coughing and congregating in shade where flies are less active. 

Wandering maggot-like larvae up to 20 mm long may be an incidental finding at necropsy when the nasopharynx is exposed during longitudinal craniotomy for brain examination.


Anthelmintics are highly effective at killing larvae.


Prevention is usually achieved incidentally with helminth control programs using macrocyclic lactones.