Myiasis Take Two

There are three further important diseases/parasites involved in myiasis. 

Hypoderma 

Hypoderma Larvae 

'Warble.' 

• Hypoderma Bovis.
• Hypoderma Lineatum. 

Abberant migration patterns and spend a long time inside the host. 

Economical Importance

• Perforation of the hide by larvae.
• 'Gadding,' fly avoidance which interrupts feeding patterns.
• Butcher's jelly- gelatinous material on tracks in the muscle by the larvae leads to carcass trimming and money loss.
• Paralysis. 

Eradicated in the UK by ELISA monitoring of infection with prevalence and import risk.

Life Cycle

1. H.Bovis lays eggs on the skin above the legs, this is the same for H.Lineatum but this parasite lays its eggs in rows on the hair. 
2. H.Bovis larvae migrate and moult to L2 where they overwinter in the cow from Nov-Mar. H.Lineatum moults to L2 stage but overwinters in the submucosa of the oesophagus from Nov-Mar. 
3. H.Lineatum pierces the hide between Mar-May as an L3. H.Bovis L3 resides in the epidural fat of the spinal cord and penetrates the back hide between May and June. 
4. Both types of larvae fall to the ground and pupate for 5 weeks.
5. The adult fly emerges in June/July and has a 1-2 week lifespan. Generally only 1 generation of eggs per year per fly. 

Diagnosis & Treatment 

• Warbles are palpable on the back hide.
• ELISA antibody detects the larval stages. 
• Treatment is with organophosphate or ivermectin.

Oestrus Ovis

'Sheep Nasal Bot.' 

Prevalent in the south. Larviparous species. 

Life Cycle

1. Adult flies in July squirt L1 up the sheep nose.
2. L1-L2 moult in the nasal passages.
3. Overwinter in the frontal sinus before moving back to the nasal cavity.
4. L2-> L3.
5. In spring the L3 fall/are sneezed out and pupate on the ground for 5-8 weeks.
6. Adults hatch. 1 generation of flies/year. 

Pathology, Diagnosis and Treatment 

• Welfare issue due to nasal discharge/sneezing.
• 'False gidding.' 
• Control via ivermectin.

Gasterophilus

'Horse Bot Fly.'

• G.intestinalis (most common).
• G.nasalis.
• G.haemorrhoidalis.

1. G.nasalis and G.haemorrhoidalis penetrate the tongue and buccal cavity whereas G.intestinalis is via eggs groomed off the fur-> L1.
2. L3 overwinters in the stomach (colic signs).
3. Faeces are passed out between feb-march where the larvae drop to the grown and pupate. 
4. Pupate for 4-6 weeks. 
5. Adult flies in July/Aug.