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

  • In warmer countries, strategic prophylactic treatment can be used


Media:Oestrus ovis.mp4