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PNEUMONIC PASTEURELLOSIS (Transit Fever) This disease is a pneumonia caused by Pasteurella species. Weaned suckled calves are usually affected soon after they have been housed. AETIOLOGY Pasteurella haemolytica biotype A serotype 1 (Al) represents about 75 per cent of the organisms isolated from cases in Britain although P.haemolytica A2 (10%) and P.multocida (10%) have also been found in the respiratory tracts of pneumonic animals. EPIDEMIOLOGY The incidence is highest in newly purchased, weaned, suckled calves from September to December when the majority of the calf sales occur. Consequently, the disease is seen predominantly in the northern and eastern areas of Britain on fattening beef farms. However, severe outbreaks with fatalities have also been confirmed in homebred, suckling beef calves housed with their dams as well as in milk fed and weaned dairy cross calves. Respiratory signs almost invariably develop within 4 weeks of suckled calves being housed (75% within 14 days) and, once the initial incident has passed, further group pneumonic episodes are uncommon. CLINICAL SIGNS Many outbreaks are called ‘transit fever * because they develop in cattle which have only been on the farm for a short time. Individuals are first seen to be standing alone and not eating. In severe incidents, the food intake of the whole group can suddenly decrease markedly. Occasional coughing may be heard, but frequent coughing is rare. Breathing difficulty and a nasal discharge may be common in the group, conjunctivitis and ocular discharge have only been seen when IBR is also involved.The morbidity and mortality rates vary greatly from group to group and from year to year. In a study involving 2026 weaned suckled calves the morbidity rate was found to be 11 per cent and the mortality rate less than 1 per cent. DIAGNOSIS The epidemiological findings and the clinical signs are usually sufficient although post mortem findings, when available, will confirm the diagnosis. In early stages of the disease, Pasteurellae species can frequently be isolated in pure culture from nasopharyngeal swabs. TREATMENT P.haemolytica is susceptible to the penicillins, oxytetracycline and trimethoprimsulphonamide and other broad-spectrum antibiotics. P.multocida has a similar susceptibility pattern. Long acting antibiotic preparations are very useful since they obviate the need for daily handling. The prognosis is good provided treatment is given during the early stages of the disease. CONTROL It is not possible to prevent the development of pneumonic pasteurellosis but physical stress factors should be minimised in newly purchased, weaned, suckled calves. If such animals are kept outside for as long as possible (at least 2 weeks) before being housed, then the prevalence and severity of the disease should be less. On some units, an injection of long-acting penicillin is given when the calves are housed and it has been claimed that this reduces the severity of the disease. Vaccination can be considered. |
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