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.

Enzootic pneumonia in Lambs

On many farms, enzootic pneumonia is an important production limiting disease, resulting in ewe and lamb deaths, failure to achieve satisfactory lamb growth rates and downgrading of carcases at slaughter. In some flocks enzootic pneumonia causes an annual lamb mortality rate of 1 - 2%. In other flocks, few deaths occur, but growth rates are reduced and lambs cough when disturbed. Most acute pneumonia outbreaks occur during late summer and early autumn.

Enzootic pneumonia results from combined infection with respiratory viruses and/or Mycoplasma spp. and Mannheimia (Pasteurella) haemolytica bacteria, which are normally present in the upper respiratory tract of healthy sheep. These pathogens are ubiquitous, thus the appearance of disease is essentially determined by predisposing management factors. The proportion of the flock affected and the severity of the disease vary, depending on stock management practices.

The principal stressors associated with outbreaks of enzootic pneumonia in the UK are persistent rain, changes to warm or cold weather, weaning and animal handling for worming or dipping. Overseas the most important predisposing management factors are hurried mustering and yarding in dry and dusty conditions. It is presumed that panting and mouth breathing associated with these conditions aids the establishment and proliferation of pathogens. Stress associated with poor nutrition or concurrent diseases such as acute liver fluke, gastrointestinal parasitism and trace element deficiencies probably reduce the animals’ immunity and enable the establishment of respiratory pathogens.

Outbreaks of enzootic pneumonia are sporadic and more severe and common in some years than in others. The most severe outbreaks are generally seen in hill and upland flocks between weaning and entering the breeding flock and in housed sheep during the winter. Severe outbreaks are characterised by sudden onset anorexia, dullness, high rectal temperatures (>40^oC) and rapid laboured breathing. Affected animals frequently mouth breathe, have a serous nasal discharge and drool frothy fluid from the mouth. The oral and ocular mucous membranes sometimes appear cyanotic. In some cases, animals are found dead. In less severe cases clinical signs may not be noted, but a high proportion of the flock is ill thrifty.

ENZOOTIC PNEUMONIA/PNEUMONIC PASTEURELLOSIS -

PURPLE COLOURED SOLID AREAS OF CONSOLIDATION

COVERED BY THICK GREENISH-COLOURED EXUDATE

Treatment and control

Whole flock long-acting antibiotic treatment can be useful in the face of an enzootic pneumonia outbreak. M. haemolytica is sensitive to oxytetracycline and tilmicosin, but some strains are not sensitive to penicillin.

Management of enzootic pneumonia depends on avoiding the important predisposing causes. Unfortunately, nothing can be done to alter the weather, but careful gathering of lambs, with the minimum use of dogs may reduce the severity of outbreaks. Buildings used for winter housing should be well ventilated, well drained to ensure dry bedding, and not stocked too densely. Ideally, introduced animals should be housed separately to avoid introduction and spread of new viruses or bacterial biotypes.

Intranasal vaccination of lambs at housing with a cattle parainfluenza type 3 virus vaccine was widely practised during the 1980s. Anecdotal evidence suggested that the practice reduced the severity of enzootic pneumonia outbreaks, but this was not proven.

Early pasteurella vaccines were not particularly useful against the most common biotype of M. haemolytica, but modern vaccines are more effective. Introduced animals are usually vaccinated twice, 3 – 4 weeks apart and a booster dose given to pregnant ewes 4 - 6 weeks before lambing, to ensure colostral protection of their lambs to 5 weeks-old. Vaccination is usually combined with clostridial disease protection. Lambs can be actively immunised from 10 days old, using two injections 3 – 4 weeks apart. However, active immunity is only short lived, so the vaccination course should be timed so that the second injection coincides with the highest risk period.

Pasteurella vaccines also provide protection against septicaemic disease in young lambs and systemic pasteurellosis in store lambs.

The recommended dose of vaccine should be administered under the skin over the neck. Clean needles should be used and regularly changed. Vaccines should be correctly stored in a dark place at about 5^oC, but protected from freezing. Vaccines should be used before their expiry date and as a general rule, partially used packs should be discarded at the end of the day.

Neil Sargison BA VetMB DSHP FRCVS