Veterinary Services

Parasitic diseases

Nematodiriasis, due principally to Nematodirus battus infection, was recorded on more than 90 occasions in Scotland during the month of June. This total represented 23.8% of diagnosable submissions for June 2006, compared to 13.9% in June 2005. A summary of Nematodiriasis outbreak diagnoses from 1995- June 2006 is shown in figure 1 (use link on the right). In most cases the condition affected lambs born between March and May, which had not received any anthelmintic treatment. In many cases morbidity rates were high and in the most severe outbreaks, mortality rates approaching 10% were recorded.

As reported last month, a small number of cases were associated with an apparent failure of efficacy by the benzimidazole class of anthelmintics in treating N. battus infection. This was indicated by the results of faecal egg counts following treatment. This finding is noteworthy given the fact that anthelmintic resistance has not been regarded as a significant problem in Nematodirus species to date and such cases will now be followed-up closely. From the perspective of the local veterinary practitioner, it is important that outbreaks of nematodiriasis, in which lambs continue to scour and/or die following dosing, should be investigated. Apart from the possibility that anthelmintic resistance is present within the worm population, there also exists the possibility of under-dosing with the benzimidazole anthelmintic, or a concurrent disease such as coccidiosis or nephrosis. It is also likely that the stress of gathering very ill, dehydrated lambs for treatment will o contribute to further deaths in the immediate post-dosing period.

Three from a group of six, eight-week-old goat kids, died suddenly over the course of a week. This group was housed and had been fed on bottled goat’s milk; hay and lamb creep since four days of age. Two of the kids were reported to have shown signs of colic prior to death, after which they were submitted for a postmortem examination at the Dumfries centre. In each case the distal half of the jejunum contained what appeared to be frank blood and the mucosa here was covered with multiple nodules of 1mm in diameter (figure 2; use link on the right). In addition the mesenteric lymph nodes were very enlarged. Within the rectum the faeces was formed but malaenic. In one case the kid was found to have been profoundly anaemic prior to death with a PCV of 3% (normal range 24 – 36%). Examination of the faeces failed to identify coccidial oocysts but subsequent histopathology revealed lesions of severe coccidiosis within the small intestine. The species involved was identified as Eimeria christenseni by its location and morphology. This species has been associated with disease in goats although it is not considered to be one of the more pathogenic species. It was assumed that the kids must have been exposed to a massive environmental challenge to die so rapidly in what was the pre-patent phase of the disease.

Alimentary tract disorders

Four ewes died suddenly from a flock of 410, with all carcases noted to be very bloated. The pasture on which the group was grazed had recently been treated with potash and phosphate. The animal submitted to the Dumfries centre had bloody ascitic fluid, with a gassy distension and congestion of the caecum and colon. Further examination confirmed a 360º torsion of the caecum around the mesentery, with the gut wall in this region being necrotic and friable. It was suggested that the underlying problem in this case might have been the availability of lush, fermentable grass.

Respiratory tract conditions

A three-month-old Cheviot ram lamb was reported to have shown signs of sneezing and to have died before treatment could be administered. At necropsy it was found to have a severe fibrinous pleurisy, from which a profuse growth of Mannheimia haemolytica was isolated. In addition a total worm count yielded 50,000 Nematodirus battus larvae and small numbers of other species.

Reproductive tract conditions

Arcanobacterium pyogenes and Prevotella species were isolated from a large epididymal abscess in a ram with a chronic unilateral testicular swelling.

Nervous system disorders

A six-week-old Cheviot lamb from a small flock in Inverness-shire died two days after being noted standing alone, hunched and grinding its teeth. The following day the condition of the lamb was said to have deteriorated, as it became laterally recumbent and showed signs of opisthotonus. On necropsy the cerebral cortex was found to have a yellowish tinge and the cerebral gyri were visibly swollen. On examination of the brain under ultraviolet light, there was seen to be multiple large areas of fluorescence in the cortex. Neuropathology confirmed this as a case of cerebrocortical necrosis (CCN); a condition that is very unusual in young sucking lambs.

The cause of blindness was investigated after four or five ewes and ewe hoggs on a croft in Skye lost sight over a five-month period. Clinical examination had revealed no corneal opacity in any of the cases, there had been no change of pasture and there was no history of significant exposure to bracken. When one of the affected ewe hoggs was submitted for postmortem examination neuropathology confirmed a chronic widespread, non-suppurative meningomyeloencephalitis. When a small number of protozoal cysts, with the appearance of sarcocysts were detected, a protozoal aetiology was suggested as the most likely cause of the neuropathology. However, on histopathology of the eye itself there was found to be changes consistent with a degenerative retinopathy, with some similarities to bracken poisoning. Unfortunately there were no additional significant abnormalities on histopathology of the viscera to help identify the cause of this retinal degeneration.

A six-week-old Scottish Blackface lamb from a flock in Inverness-shire was found unable to stand. The lambs had received a prophylactic treatment for ticks one-month previously. On neuropathology there was a non-suppurative meningoencephalitis consistent with louping ill. This diagnosis was supported when serological examination detected antibodies to louping ill virus at a titre of 1/320; a proportion of which was IgM consistent with recent infection

A group of 150 Scottish Blackface ewes and their lambs were moved to Highland hill ground, which had not been previously grazed by the flock. The group was dipped using an organophosphate product some two weeks later, after the ground was found to be heavily infested with ticks. By this point there had been a number of lamb deaths within the group including one case this being identified as due to pasteurellosis and nematodirosis. The deaths did cease for a time after the dipping and treatment of the lambs with anthelmintic and a long acting tetracycline antibiotic. However, the following week, ten ewes and approximately ten lambs died over the space of a few days prompting the submission of two lambs and two ewes for postmortem examination. The first lamb was diagnosed with tick pyaemia, while both lambs and one of the ewes showed both serological and histopathological evidence of louping ill.

Skin diseases

A two-year-old, Cheviot gimmer from a flock in Ross-shire was found to have an abscess on its head. The purulent contents of this lesion were cultured due to concerns over caseous lymphadentitis. A moderate growth of Arcanobacterium pyogenes was isolated. On another unit a bought-in Texel ewe developed an abscess in the submandibular area. In this case a profuse growth of an Actinomyces species and a mixed growth of anaerobes, including Fusobacterium necrophorum subsp. necrophorum, was isolated on culture.