Caseous Lymphadenitis (CLA) – cheesy gland – is a common chronic disease in sheep and goats. It occurs in around 97% of flocks in NSW and is responsible for up to 50% of condemned sheep carcasses at slaughter. The cheesy gland organism, the bacterium Corynebacterium pseudotuberculosis, causes abscess formation in the lung, liver, spleen, kidneys and lymph nodes of infected sheep.
The loss of CLA carcasses costs meat producers over $14 million per year and for wool producers, annual wool losses of $15-20 million.
Sheep affected by cheesy gland are often less productive and can lose around 4-7% of their clean wool production. CLA can also affect ram and ewe fertility – the disease leads to mastitis and uterine infections in ewes, and abscesses in the testes of rams.
Clinical signs
There are two forms of the disease. Both occur in sheep and goats, the superficial form is more common in goats, and the visceral (internal) form more often diagnosed in sheep. In goats, cheesy gland can be fatal and affected goats in milking herds should be culled.
In the superficial form, abscesses form in lymph nodes near the skin surface – most commonly around the head, neck, shoulder and flanks. The nodes become enlarged and will eventually burst, releasing a thick purulent (pus) discharge. The second form of the disease involves abscess formation in lymph nodes associated with internal organs, usually the lungs, kidney, liver and intestine.
While many infected animals don’t show clinical signs, CLA can cause a range of symptoms: decreased wool production, weight loss, coughing or superficial abscess formation as above.
Cheesy gland spreads through a flock in a number of ways – through contact with pus from abscesses, or most frequently, via airborne bacteria from coughing sheep. Management practices can encourage spread – holding sheep under cover after shearing, or the use of dips contaminated by sheep with open abscesses.
Prevention
Treatment of cheesy gland is impractical and prevention by vaccination is recommended. Cheesy gland vaccine is included in 3-in-1 and 6-in-1 vaccines. Lambs should be vaccinated at marking and again at weaning, followed by annual boosters 4-6 weeks before shearing. To ensure immunity, it is critical that two doses of vaccine are given close together to establish initial good protection, and lambs must be vaccinated twice before their first shearing.
The spread of cheesy gland can be minimised in a flock by:
- disinfecting shears regularly
- shearing lambs first
- releasing sheep as soon as possible after shearing
- avoiding dipping off shears unless shearing cuts have healed and animals have been vaccinated against the disease 4-6 weeks before shearing.
Crookwell Veterinary Hospital stocks vaccines protecting against cheesy gland. We strongly recommend any vaccination schedule in sheep flocks – for both wool or meat producers – includes protection against cheesy gland.
Article acknowledgment: Dini Hapukotuwa, veterinary student, Faculty of Veterinary Science, University of Sydney. CVH is a Faculty of Veterinary Science Partner Practice and Dini spent 4 weeks at CVH in 2015 as part of her final year practical rotations.