Clinical cases associated with each species have a seasonal distribution with P.haemolytica more prevalent in the spring and summer and P.trehalosi in the autumn.

P.haemolytica

This is a disease of both lambs and ewes and most outbreaks occur in May, June and July. Flock outbreaks often start with sudden deaths in young lambs. These sudden deaths are due to an overwhelming septicaemia rather than pneumonia. Lambs older than three months and adults are more likely to present as pneumonia. Pneumonic pasteurellosis can be seen as an individual sheep problem.

Enviromental factors can predispose flocks to an outbreak. Stresses such as warm,cold or wet weather, dipping, castration and dosing can be linked to subsequent outbreaks. Concurrent infection with respiratory viruses can also predispose flocks.

Clinical signs include sudden death, dullness, anorexia and high temperature. The animal will show varying degrees of respiratory distress. Discharge from the eye and nose will be noticed.

P. trehalosi

This usually affects sheep 6-9 months old in October, November and December. Predisposing factors include a change to cold, wet weather, and turning out onto improved pasture. The main feature of the disease is sudden death with numbers being highest at the onset and quickly dropping over a few days.

Treatment and Prevention

Treatment with antibiotics can be helpful either as a response to disease or as a prophylactic measure. However due to the sporadic nature of pasteurellosis, vaccination is the recommended course of action. The vaccine for pasteurella is a combined vaccine which also covers the clostridial diseases. The primary course for naïve sheep is two injections 4-6 weeks apart. The second of which should be given in the pre-lambing period, 4-6 weeks before lambing. A booster is required every year, again to be given 4-6 weeks prior to lambing. This aids in the control of the disease in young lambs. Lambs that are retained for fattening or as future breeding will require a primary course once they are over 3 weeks of age.