Blowfly Strike 🪰
Blowfly strike, also known as cutaneous myiasis or maggots, is a serious condition in sheep caused by the larvae of certain fly species such as the greenbottle fly (Lucilia sericata), blackbottle fly (Phormia terraenovae), and bluebottle fly (Calliphora erythrocephala). These flies lay their eggs on soiled fleece or wounds, and the hatched larvae feed on the sheep's tissue, causing significant damage and distress.
Symptoms and diagnosis of blowfly strike in sheep 🩺
Blowfly populations peak during the summer months, but due to climate changes, the risk period can extend from March to December in some areas. The entire lifecycle from egg to adult fly can occur in less than 10 days under optimal conditions.
Symptoms
Sheep affected by blowfly strike may show the following signs:
- Disrupted grazing patterns and rapid weight loss
- Agitation and dejection
- Stamping of hind legs, shaking tails, or gnawing and rubbing at the affected area
- Distinctive foul odor from the affected area
- Matted and discolored wool
- Visible maggots on the skin once the fleece is lifted
The back end of the sheep is most commonly affected, but lesions can also appear on the withers, back, shoulders, and head.
Diagnosis
Diagnosis is based on visual inspection. Look for large numbers of adult flies on discolored fleece and maggots on blackened skin. There is often a putrid smell associated with the lesions. It is a legal requirement to inspect all sheep daily during high-risk periods for signs of blowfly strike.
How to treat blowfly strike in sheep 💊
Treating blowfly strike involves several steps:
- Physically remove the maggots from the affected area.
- Clean and disinfect the wounds.
- Provide supportive treatment such as antibiotics, fluids, and non-steroidal anti-inflammatories (NSAIDs) under the direction of a vet.
- Plunge dipping using an organophosphate preparation can be undertaken, but it is more common to treat individual animals with dip wash applied directly to the struck area after clipping away the overlying wool.
How to prevent blowfly strike in sheep 🛡️
Preventing blowfly strike is crucial and involves several strategies:
- Regularly inspect sheep, especially during high-risk periods.
- Maintain good hygiene by keeping the fleece clean and free from soiling.
- Use preventive chemical treatments such as cypermethrin, alpha-cypermethrin, diazinon, deltamethrin, dicyclanil, and cyromazine. These chemicals provide varying lengths of protection and have different withdrawal periods, so consult your vet for the best option for your flock.
- Ensure proper wound management to prevent fly attraction.
- Consider shearing sheep before the high-risk period to reduce the amount of fleece that can become soiled and attract flies.