Veterinary Services

Parasitic diseases

The number of outbreaks of parasitic gastroenteritis (pge) and chronic fasciolosis increased this month. In one outbreak a six-month-old lamb was submitted from a unit in Aberdeenshire where both ill-thrift and a number of deaths had been reported. The affected carcass was in extremely poor body condition and post-mortem examination confirmed the presence of both an acute bacterial bronchopneumonia, due to infection with Arcanobacterium pyogenes, and significant parasitic gastroenteritis. As these lambs had reportedly been wormed five weeks previously, it was suggested that although the high worm burden could be due to reinfection from heavily contaminated pasture, the possibility of anthelmintic resistance should also be considered.

Generalised and systemic conditions

Systemic pasteurellosis associated with infection with Pasteurella trehalosi was a frequent diagnosis amongst this year's lambs, folded outside on root crops, kale or grass. Mortality rates as high as 7.5% were recorded on some premises. Although in most cases the history indicated either an absent or incomplete programme of vaccination with a multivalent Pasteurella product, some outbreaks appeared to occur despite the use of vaccines as recommended.

The St Boswells Centre was involved in the investigation of chronic wasting amongst rams in a stud, run as part of a commercial upland flock. A total of seven of the 55 mostly Suffolk rams within this group were said to be affected. When three of the wasting animals were submitted for necropsy, one ram showed thickening of mucosa in the distal small intestine. Subsequent histopathology confirmed sparse numbers of acid fast bacilli and pathological changes consistent with a diagnosis of paucibacillary Johne's disease. However when the other two rams were examined no such changes were seen. Instead, both were found to have a series of abscesses within the mediastinal lymph node chain. These ranged in size from the diameter of a golf ball to that of a tennis ball. The contents of the abscesses were caseous in nature and subsequent bacteriology confirmed a pure growth of Corynebacterium pseudotuberculosis, the causal agent of caseous lymphadenitis (CLA). Necropsy of one of these two rams also revealed an area of pleurisy and a lung abscess, from which the same organism was recovered. An association between ill-thrift and the presence of CLA abscesses within the thorax has been recognized in North America and noted in the UK on previous occasions (SAC Surveillance Report June 2004, VLA Surveillance Report June 2005).

Alimentary tract disorders

A Cheviot cross ewe was found dead with swelling of the neck and fresh blood at the mouth. A 1.5cm diameter circular wound was noted in the wall of the pharynx which contained a large blood clot and a focus of necrosis, which appeared to extend through the wall of adjacent blood vessels. Arcanobacterium pyogenes and a Bacteroides species were subsequently isolated from the lesion. The history in this case indicated a previous dosing gun injury and the farmer reported losing two other ewes and two lambs with similar symptoms.

Two faecal samples from a group of seven-month-old Hampshire Down lambs were submitted to the Edinburgh Centre with a history of chronic diarrhoea, despite regular anthelmintic treatment. Worm egg and coccidial oocyst counts were insignificant and Salmonella cultures proved negative. However selective Yersinia cultures yielded a growth of Yersinia enterocolitica from both samples. Yersiniosis in the UK has been described as a condition of high morbidity and generally low mortality, commonly associated with concurrent stress, such as inclement weather or weaning.

A four-year-old Mouflon ram from a wildlife park in the Inverness area was diagnosed with the paucibacillary form of Johne’s disease. This animal had been losing weight over a number of weeks and latterly developed diarrhoea. Grossly a mild thickening of the small intestine and the mucosa along the distal ileum with a velvety appearance was noted. However histopathology revealed evidence of widespread chronic granulomatous enteritis, with epithelioid and giant cell infiltrates. Subsequent Ziehl-Neelson staining confirmed the presence of sparse acid/alcohol fast bacteria in epithelioid cells within the intestinal mucosa. A diagnosis of Johne’s disease was also reached when a three-year-old African Pygmy goat was necropsied at Ayr after showing diarrhoea and chronic weight loss. In addition a severe hypocuprosis was demonstrated, with liver copper recorded as less than 65 µmol/kg on a dry matter basis (reference range – 314-7850 umol/kg DM).

Ruminal acidosis was diagnosed at the Perth Centre in lambs from two premises. On both occasions the affected lambs were grazing stubble fields. In the first case three, six-month-old Texel lambs died from a group of 40, with a submitted carcass showing ruminal tympany. Whole grains were evident within rumen contents, which were found to have a pH of 4.5. Similar findings were recorded when two, six-month-old Cheviot lambs died on another farm under similar circumstances.

Respiratory tract conditions

Just as systemic pasteurellosis was diagnosed frequently this month, so the pneumonic form of the disease, due to infection with Mannheimia haemolytica was recorded on seven occasions during October. In one outbreak in the Scottish Borders, a total of 12 deaths occurred in a group of 220 Scottish Blackface ewe lambs on a silage aftermath. Noteworthy in this case was the fact that mortality was restricted to the batch of 103 homebred lambs, with the purchased lambs running in the same fields apparently unaffected – representing a mortality rate of more than 10% within this homebred group. Reference to the clinical history in this case revealed that the homebred lambs had received only the first dose of a Pasteurella vaccine at the time of the outbreak, while the purchased animals were believed to have received a full course of vaccination.

Reproductive tract conditions

A unit in western Aberdeenshire routinely moves its gimmers to hill grazings for the summer, bringing them home in October for breeding. A high barren rate was reported at the mid-gestation scanning of this gimmer group for two consecutive years, whilst fertility within the rest of the breeding flock has been satisfactory. Previous investigations had failed to confirm involvement of enzootic abortion or toxoplasmosis. This year blood samples from the returning gimmers confirmed exposure to tick borne fever – raising suspicions that this infection may have been responsible for the poor fertility in previous years. Advice has now been given to bring future groups of gimmers off the hill earlier in the autumn, in order to avoid the period of increased tick activity.

Nervous system disorders

Louping-ill was diagnosed in a two year old Scottish Blackface gimmer from a flock in Inverness-shire. One previous death had occurred in the group in an animal that presented with signs of ataxia and tremor. The antibody titre to louping-ill virus was found to be 1/2,560, much of which was IgM, consistent with recent infection by the virus.

Skin diseases

The contents of a submandibular abscess from a Scottish Bluefaced Leicester ewe were submitted to the Edinburgh Centre, where a pure growth of P. trehalosi was isolated.