Systemic Pasteurellosis

NADIS disease bulletins are written specifically for farmers, to increase awareness of prevalent conditions and promote disease prevention and control, in order to benefit animal health and welfare. Farmers are advised to discuss their individual farm circumstances with their veterinary surgeon.

January 2004

By Neil Sargison BA VetMB DSHP FRCVS

NADIS Sheep Disease Focus

Systemic Pasteurellosis

Over a period of 5 days at the end of October, 7 of 120 store lambs were found dead, or died within a few hours of being seen ill. 

Another three lambs recovered following prompt treatment for acute onset, severe respiratory disease. The 38 – 45 kg lambs had recently been moved onto good pasture in the south-east of Scotland and were nearly finished.

6% OF A GROUP OF SUFFOLK AND TEXEL CROSS LAMBS DIED WITHIN A FEW HOURS OF BEING SEEN ILL

On postmortem examination of dead lambs, the lungs were dark purple and blotchy indicating generalised congestion and subpleural haemorrhages. The linings of the trachea and bronchi were dark red and exuded frothy blood tinged fluid. 

Cut surfaces of the lungs oozed foam and mucus. There was, however no evidence of lung consolidation or plurisy. The laryngeal mucosa had a roughened and congested appearance. These findings were consistent with systemic pasteurellosis.

DARK PURPLE AND BLOTCHY LUNGS TYPICAL OF SYSTEMIC PASTEURELLOSIS

The first signs of illness were sudden onset dullness, a slight purulent nasal discharge, congestion of mucus membranes and increased respiratory rate and effort, leading rapidly to a state of recumbency and to death within a few hours.

CONGESTION OF THE OCCULAR MUCUS MEMBRANES – WHEN IDENTIFIED PROMPTLY, SOME AFFECTED LAMBS RESPOND TO TREATMENT INCLUDING INTRAVENOUS CORTICOSTEROID AND SYSTEMIC ANTIBIOTIC INJECTIONS

There were numerous other reports of systemic pasteurellosis during the same period, mostly from the south of Scotland.

Systemic pasteurellosis is the most commonly diagnosed cause of sudden death in store lambs between October and December. Mortality rates of 20% have been reported, but losses of about 2% are more commonplace. 

Systemic pasteurellosis is caused by the bacterium Pasteurella trehalosi, but the reasons for disease outbreaks are not fully understood. Outbreaks frequently follow movement of lambs onto rape, turnips or improved pastures. Wet and cold weather has also been implicated. 

P. trehalosi is found in the tonsils and upper gastro-intestinal tract of healthy sheep and it has been suggested that under certain stressful conditions, the bacteria multiply and spread rapidly to the lungs and other organs. Concurrent diseases such as cobalt deficiency or tick borne fever may also predispose to outbreaks of the disease.

In the face of an outbreak of systemic pasteurellosis, whole flock treatment with a single injection of long-acting antibiotic may help to prevent further losses, although the stress of gathering and injecting the lambs may itself precipitate some deaths. 

It is, therefore, impossible to determine the effectiveness of this strategy and the decision to treat or not is based on individual flock circumstances.

Prevention of systemic pasteurellosis is also problematic. Avoidance of nutritional stress and wet weather conditions, which predispose to the disease, is difficult and pasteurella vaccines only afford variable short-lasting protection.

• While every effort is made to ensure that the content of this forecast is accurate at the time of publication, NADIS cannot accept responsibility for errors or omissions. All information is general and will need to be adapted in the light of individual farm circumstances in consultation with your veterinary surgeon.

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