Lumpy wool disease in sheep

What is lumpy wool?

Lumpy wool, or 'dermo', is a contagious bacterial infection caused by the bacterium Dermatophilus congolensis. The infection inflames the skin and forms hard scabs that lift from the skin as fleece grows, resulting in the characteristic lumpy wool.

Lumpy wool disease in sheep can occur after prolonged rainfall. It results in loss of condition, reduced skin/wool value, and possible death in affected mobs.

When to watch out for it

Lumpy wool often develops following prolonged wetting of the fleece and skin. The bacteria are dormant on the skin when dry, but spread rapidly when wet, causing skin discharge and scab formation.

Lumpy wool mainly occurs in weaners or hoggets, especially those with a fleece type that wets easily. Young lambs less than six weeks of age are susceptible due to the low protective wax content of their wool. Wet weather coinciding with lambing presents high-risk conditions as the infection spreads from the ewe to the newborn lamb.

Clinical signs

Infection causes the skin to become inflamed. Serum, pus and dead skin repeatedly lift into the fleece forming scabs.

• Columns of hard lumps form along the wool staple
• Scabs are more significant on woolled areas; advanced cases have hard lumps or plates of scabs across the back
• In non-wool areas such as the face and ears, scabs are generally less than 1 cm in diameter
• Scabs lift from the skin with the fleece as it grows, causing the characteristic lumpy wool appearance

What is the difference between lumpy wool and fleece rot?

Because the cause and treatment of lumpy wool is different to fleece rot, it is important to differentiate between the two:

• Lumpy wool tends to form columns of hard lumps along the wool staples.
• Fleece rot appears as crusty, discoloured bands parallel to the skin.

How to manage

To reduce the spread and impact of lumpy wool:

• Separate infected sheep from the flock to help reduce spread and assist blowfly management.
• Limit physical contact between wet sheep and avoid yarding wet sheep.
• Shear and dip young sheep first, before the area becomes contaminated by older carriers.
• Shear or dip infected sheep last.

How to treat

• Most sheep will develop immunity, and in most cases the active skin infection heals within four to six weeks.
• In severe cases, sheep can be treated with antibiotics.
• Cull chronically infected sheep due to their ongoing susceptibility to flystrike.

How to prevent

• Use commercially available dip additives (e.g. 0.5% zinc sulphate solution) as a preventative.
• Maintain good shearing and dipping order to reduce contamination risk.
• Avoid yarding wet sheep and minimise contact between wet and dry animals.