How does myiasis develop?
The fly lays clusters of 1000 to 3000 eggs in the sheep’s wool. This can occur anywhere on the body. Within hours to days, the larvae hatch. These larvae need moisture to survive, which is why they develop particularly well in wet, dirty or dense wool. This includes areas with:
- urine or faecal contamination
- small wounds
- wet or dirty fleece
The first damage can occur within 4 hours after contact with the larvae. After 24 hours, the condition worsens rapidly, and within 48 hours deep skin damage can develop. In severe cases, a sheep can die within 5 days.
Not every sheep is equally attractive to flies. Smell likely plays a role, although this is not yet fully understood.
What are the signs of myiasis?
Sheep with myiasis behave differently. In the early stages, you may notice subtle changes.
Animals experience itching and may:
- rub themselves
- bite at their skin
- show restless behaviour
As the condition progresses, sheep become lethargic, eat less and deteriorate quickly.
The wool and skin at the affected area are often moist, discoloured and have a strong odour. Large numbers of maggots are usually visible in the wound. Once the skin is damaged, these areas attract even more flies, causing the problem to worsen rapidly.
Treatment of myiasis
Myiasis is an emergency and must always be treated immediately.
Treatment involves carefully examining the animal and addressing all affected areas. The wool around dirty or affected areas is clipped away, after which the maggots are removed as thoroughly as possible. The areas are then treated with a suitable product, such as diazinon.
In cases of severe skin damage, additional treatment by a veterinarian may be required, for example with antibiotics.
Preventing myiasis
Prevention plays a major role but requires a well-considered approach.
The development of maggots strongly depends on moisture in the wool. Factors such as wool length, density and contamination are important. Shearing is therefore an effective preventive measure. Wool shorter than 2.5 cm makes it difficult for larvae to develop.
Many sheep farmers choose to shear around lambing time. This means that myiasis is rarely seen in the months immediately afterwards. However, it is important to realise that winter shearing can also have disadvantages, depending on when myiasis typically occurs on the farm.
There are also preventive products available, such as dicyclanil and diazinon. These offer protection for several weeks to months, but it is important to use them only when truly necessary. Routine treatment from April to October is usually not advisable and may contribute to resistance and environmental impact.
Key considerations for prevention
Not every farm experiences myiasis every year. It is therefore advisable to:
- check animals regularly
- stay alert for the first cases
- use preventive products only when needed
Breeding also plays a role. Susceptibility to myiasis is partly hereditary. By selecting less susceptible animals, the problem can be reduced over time.
Safe use of products
When using products such as diazinon, caution is important. This substance is also harmful to humans. Protect yourself properly with gloves, protective clothing and preferably a mask and goggles. Work outdoors whenever possible and avoid skin contact.
Myiasis is a serious but often preventable condition. The key is to act quickly at the first signs and to check your flock regularly. Prevention is important, but should always be applied in a targeted and considered way.
Are you unsure whether you are dealing with myiasis? Always contact your veterinarian. Prompt treatment can make all the difference.
