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Introduction
Myiasis is the parasitism of living animals by dipteran larvae. Myiasis can be oligatory or facultative (optional) and is described as cutaneous, nasal or somatic.
Oestridae
- The larvae of Oestridae spp. are obligatory parasites
- The three important species of veterinary interest are Hypoderma, Oestrus and Gasterophilus
Hypoderma spp.
- Also known as warble flies
- Important cattle parasites
- Also parasitise horses, small ruminants and sometimes humans
- The two main species in cattle are H. bovis and H. lineatum
- H. diana parasitises deer
- Infestation is largely confined to the Northern Hemisphere
Recognition
- Large 13-15mm long
- Similar to bumble bees in appearance
- Yellow abdomen
- Band of black hairs
- One pair of wings
Life Cycle
- Adult flies emerge on warm, sunny days between June and August
- White eggs are laid around the belly and legs of the animal
- Eggs are attached to hairs by cement and a small terminal clasp
- H. lineatum lays a whole row of eggs as it approaches the animal stealthily
- H. bovis only deposits a single egg before the animal runs away ('gadding) as it makes a loud buzzing noise
- The adult lives for 3 weeks
- Females can lay several hundred eggs in their life
- A few days after eggs are laid, larvae emerge and crawl down the hairs into the hair follicles
- Larvae penetrate the skin through wounds made by biting flies
- Larvae migrate through the subcutaneous tissue towards the diaphragm
- Enzymatic secretions and mouth hooks aids larval migration
- After 3 months larvae reach winter resting sites where they remain from November to Feburary/March whilst moulting to the L2 stage
- Epidural fat in the spinal canal for H. bovis
- Wall of the oesophagus for H. lineatum
- Larvae then migrate back to the subcutis along the midline of the back where they bore a breathing hole through the skin and moult to the L3 stage
- Larvae are palpable as distinct swellings called warbles
- L3 larvae emerge after 4-10 weeks where they fall to the ground and pupate under loose vegetation
- Adult flies emerge from the pupa after one month where they copulate, lay eggs and die within two weeks
- H. lineatum are on the wing 6-8 weeks before H. bovis
- There is only one generation of warble flies per year
Pathogenesis
- Causesmyositis
Control
Oestrus ovis
- Also known as the sheep nasal bot fly
Recognition
Life Cycle
Pathogenesis
Control
Gasterophilus spp.
- Also known as the horse bot fly
Recognition
Life Cycle
Pathogenesis
Control
Dermatobia hominis
Recongition
Life Cycle
Pathogenesis
Control
Calliphoridae
Recongition
Life Cycle
Pathogenesis
Control
Screw Worm Myiasis
Recongition
Life Cycle
Pathogenesis
Control
Wohlfahrtia sp.
Recongition
Life Cycle
Pathogenesis
Control