Oestriasis

infestation of sheep with botfly larvae that parasitize the paranasal and frontal sinuses. The disease is prevalent in sheep-raising countries, causing great economic harm by lowering meat, wool, and milk productivity.

The causative agent is the viviparous female botfly Oestrus ovis, whose larvae enter the sheep’s nostrils and develop first on the mucous membrane of the turbinate bones and then in the frontal sinuses and horn cavities. The larvae traumatize the mucous membrane of the upper respiratory tract, causing a mucopurulent inflammation and tissue destruction (necrosis). Most infected sheep have copious mucupurulent and bloody discharges from the nasal passages and have difficulty breathing. Sometimes the disease is fatal.

Treatment includes washing the nasal passages or introducing a larvicide (for example, trichlorfon solution) into the frontal sinuses. Prevention involves treating the animals with insecticides and repellents during the swarming period of the botflies.