Oestrus ovis
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- Also known as the sheep nasal bot fly
- Larvae parasitise the nasal chambers of sheep and goats
- Found in most sheep rearing areas of the world
Recognition
- 13-15mm long
- Grey colouring
- Black spots on abdomen
- Clear wings
- Larvae have distinct black bands on each body segment
Life cycle
- Larvae are squirted into the nostrils of sheep in a jet of liquid by the adult fly
- The larvae crawl caudally into the nasal cavity and feed on the nasal mucosa and mature before returning to the nostrils
- Larval development takes up to 2 months
- Larvae can overwinter in the nasal cavity if deposited late in the summer
- Once the larvae have developed they are sneezed out and pupate on the ground
- The adult fly emerges 1 months later
- Adult flies only live for 2-3 weeks
Pathogenesis
- Adult flies cause annoyance
- Interrupts feeding
- Leads to a decreased weight gain
- Larvae cause nasal irritation, nasal discharge and sneezing
- Irritate the nasal mucosa with oral hooks and spines causing a viscous exudate to be produced from which they feed
- Heavy infestations lead to erosion of the bones in the sinuses (turbinate bones)
- Penetration of the brain leads to false gid (high stepping gait and incoordination)
Control
- Systemic insecticides can be used in heavy infestations
- In warmer countries, strategic prophylactic treatment can be used
- Larvae in the nasal cavity of sheep and goats = Nasal bots
- Causes reaction in sinuses