Veterinary Services

Parasitic diseases

Eight cows died in a 250-cow herd in Aberdeenshire that had grazed marshy fields with a history of redwater. The cows were treated with deltamethrin in May but then not treated again until two weeks previously at weaning when a few ticks were observed on some of the cows. None of the sick cows had responded to treatment with imidocarb. The farm was visited and a postmortem examination was carried out. Babesiosis was confirmed in a live sick cow by demonstration of Babesia divergens in a blood smear. The diagnosis was suspected in the dead cow. The stress of weaning and a concomitant increase in tick activity were suspected to be predisposing factors in the outbreak.

Generalised and systemic conditions

As reported previously (Veterinary Record; 25 August 2007, pages 249-252) there is an increase in the number of confirmed Malignant Catarrhal Fever (MCF) cases in beef suckler herds in Shetland, Orkney, Caithness and Sutherland in 2007. Eight of the 19 outbreaks diagnosed by SAC between January and August were in this region that is served by the Thurso Centre. This figure compares with a total of 20 outbreaks recorded by Thurso between 1993 and 2006 with between none and four in any one year. Most cases were single occurrences in large or small herds affecting animals aged three months to four years. In some of the cases there was no direct contact with sheep or deer (there are no deer in Shetland and Orkney) but in others there was during their lifetime. The presenting clinical signs have been unusual in some cases with the initial problem being diarrhoea, pyrexia and then depression with facial swelling, upper respiratory tract and eye lesions being last to appear. The majority of cases became clinically severe and most were humanely destroyed. The diagnosis was confirmed by examination for MCF antibody in serum. In some cases blood samples may have been collected very soon after the appearance of clinical signs and no antibody has been detected but the progression of symptoms has been typical of the disease. A PCR test can be used to detect the MCF virus if heparinised blood is submitted. Further investigations into these outbreaks include postmortem examinations of cases and the investigation of possible risk factors.

Alimentary tract conditions

The carcase of a three-month-old beef suckler calf was submitted from a farm in Fife. The calf had been found collapsed, cold and dehydrated. At necropsy the lungs were congested and the liver was an orange/brown colour. There were occasional patches of haemorrhage evident on the luminal surface of the abomasum. The small intestine was thickened, pale and empty while the large intestine thickened and pale but contained watery contents. Histological findings indicated severe damage to the intestines and kidneys. The small intestine showed dramatic mucosal distortion with dilation of the glands, attenuated epithelium and fibrosis. This was accompanied by a mild interstitial lymphocytic infiltrate. The large intestine showed collapse of the mucosa into the submucosal lymphoid deposits. Changes in the kidneys were consistent with a patchy chronic interstitial nephritis. There was extensive, acute tubular degeneration and necrosis with interstitial congestion. Proteinaceous debris was present within the damaged tubules. These changes were typical of necrotising enteritis syndrome, which affects single, suckled calves.

Respiratory tract conditions

Lungworm infection was again a common diagnosis across Scotland this month. 18 outbreaks were recorded. This compares with 3 in August 2006. A two-year-old dairy heifer was submitted for postmortem examination from a herd in Ayrshire with a history of poor milk yields and coughing. Faecal samples from seven affected animals were submitted previously and all had been negative for lungworm larvae. Postmortem examination revealed a heavy burden of lungworm evident in the trachea, bronchi and bronchioles (figure 1 - see top right-hand side). There was anteroventral consolidation of the left lung lobes and emphysema of the right lung lobes. Unlike the earlier faecal samples from the herd, lungworm larvae were detected in the caecal contents of the animal that died. The SAC considers that the failure to detect larvae in the faecal samples may have been due to pre-patent infection at the time of sampling.

Reproductive tract conditions

St Boswells identified Campylobacter fetus fetus as the cause of abortion in a 12-year-old pedigree Limousin cow, the only affected animal in a 10-strong herd.