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Bolo disease: a specific, localised skin disease of woolled sheep.

Bolo disease is limited to Merino and Döhne merino sheep in the Stutterheim and Cathcart districts of the eastern Cape Province. It occurs under natural grazing conditions regardless of the season of the year and the condition of the natural grazing. Ewes and wethers are most frequently affected. Skin lesions are well-defined, and the corresponding fleece has dark-grey to almost black spots, patches or bands varying in number, size and distribution between individual sheep. The wool in the affected areas is visibly shorter, less dense and tender, and the tips of the staples are spiky. In freshly-shorn sheep, the affected areas appear chalky white. Chronic and superimposed acute lesions are present in the same specimen histologically. Skin lesions include superficial and follicular hyperkeratosis, acanthosis, and sebaceous gland hyperplasia and hypertrophy. These changes are accompanied by dilatation of some of the follicles in the midshaft area, and collapse of the subepidermal tissue with only a few remaining collagen fibres separating the follicles and the sebaceous glands from the thickened epidermis. Corynebacterium spp. is the most consistent bacterium isolated from the lesions. Lesions produced by suspensions of this organism simulated both clinical signs and histopathological findings of the natural condition.

Animals↗

Environmental influences on the progression of clinical and microbiological parameters of sheep periodontal disease.

The responses of some clinical and microbiological parameters of periodontal disease (PD) in sheep were examined subsequent to transferring animals between PD-affected and PD-free farms. Previously healthy animals showed transient deterioration in some clinical, but not microbiological parameters, which suggests either that a different microbiota to the one studied may be more important in the initiation of the disease, or that sampling did not intercept periods of destructive disease activity in the early lesions. In sheep with established disease, those parameters indicative of periodontitis which included pocket depth and bleeding on probing as well as the proportions of black-pigmented Bacteroides species were not significantly altered by environmental changes. This observation suggests that once the disease is established on PD-affected farms, the hand, some clinical signs of the disease including lengthening and mobility of incisor teeth increased in sheep on the PD-affected farm relative to the PD-free farm. This suggests that the disease may have a complex aetiology.

Animals↗

New transtracheal bronchoalveolar lavage technique for the diagnosis of respiratory disease in sheep.

A new transtracheal bronchoalveolar lavage technique for the diagnosis of respiratory disease in sheep under field conditions was tested in 76 sheep. The sheep were divided into three groups, normal sheep, sheep with clinical signs of respiratory disease and housed sheep, on the basis of their respiratory disease history and husbandry conditions. The detection of Mannheimia haemolytica and Mycoplasma ovipneumoniae or parainfluenza virus type 3 and bovine respiratory syncytial virus antigen in the lavage samples was closely correlated with clinical disease. The sheep with clinical respiratory disease had a higher mean percentage of neutrophils in the lavage fluid than the sheep in the other two groups.

Animal Husbandry↗

Ovine lentivirus is aetiologically associated with chronic respiratory disease of sheep on the Laikipia Plateau in Kenya.

A study was undertaken to investigate the occurrence of ovine lentivirus (OvLV) infection in sheep with chronic respiratory disease on the Laikipia Plateau, Kenya. All seven Merino crossbred sheep with chronic dyspnoea and emaciation examined for gross and microscopic lesions had lymphoid interstitial pneumonia (LIP), and one also had pulmonary abscesses. Two of the sheep with LIP also had lesions of ovine pulmonary carcinoma (OPC, jaagsiekte). Using in situ hybridization, OvLV DNA localized to a high proportion of pulmonary macrophages in lungs with lesions of LIP. Lung tissue samples from six of these sheep were positive for a syncytium-inducing virus in cultures of lamb testis cells. Thin-section electron microscopy of infected cells showed virions with morphogenesis typical of lentiviruses. In a western blotting assay, monoclonal antibodies to the OvLV capsid (CA, p27) and matrix (MA, p15) proteins of a North American OvLV isolate reacted with similar-sized bands of the virus, and serum from six of the sheep were reactive with CA from the Kenyan viral isolate. Using an OvLV agar gel immunodiffusion (AGID) test, all seven sheep were positive for serum antiviral antibody, as were 29% of 63 clinically normal sheep from Laikipia District. However, when sera from the healthy sheep were tested in a western blot assay, only 52% had IgG reactive to the OvLV CA, indicating a high rate of false negative reactions with the AGID test. Serum samples from 87 Red Maasai or Dorper crossbred sheep from two farms in other parts of Kenya were OvLV seronegative by both the AGID test and the western blot assay. These results document the first identification of OvLV as a cause of chronic respiratory disease in sheep in Kenya and show a high rate of infection in sheep flocks, with a high prevalence of chronic respiratory disease.

Animals↗

Border disease in sheep.

The current knowledge on border disease in sheep is reviewed. This is a congenital and teratogenic disorder induced by pestivirus. The history, etiology, epidemiology, clinical aspects, and pathologic lesions at postnatal and intrauterine infections (as well as in congenitally affected animals), pathogenesis, immunity, diagnosis, and control and prevention of the syndrome are discussed.

Animals↗

White liver disease of sheep.

Outbreaks of ovine white liver disease (WLD) on 7 farms in eastern Victoria were investigated. Most occurred in late spring and mainly affected lambs 3 to 6 months old, with a morbidity of 20 to 100% and mortality of 8 to 15%. Clinically affected lambs showed illthrift, emaciation and bilateral, serous, ocular discharge. Clinical pathology showed mild anaemia, elevated serum liver enzymes (GGT, OCT, AST) and low levels of serum vitamin B12. Grossly, the livers were pale, fatty and friable; microscopically there was parenchymal fatty change, bile duct proliferation and ceroid pigmentation. Liver cobalt values were consistently low (mean 0.4 +/- 0.4 mumol/kg D.W.). Levels of cobalt in pasture from 2 properties were very low (0.34 mumol/kg D.W.) The diagnosis of white liver disease was made on the basis of clinical features, specific liver pathology and low cobalt status. Treatment trials established that cobalt injections or oral bullet administration resulted in clinical improvement, significant weight gains, and improved serum vitamin B12 levels. WLD did not recur in previously affected sheep using these treatments. However, when blocks containing cobalt were available continuously, WLD recurred 2 years after the initial outbreak.

Animals↗

Introduction to the transmissible spongiform encephalopathies or prion diseases.

Sheep scrapie has been known for at least 200 years and was described as a transmissible disease over 100 years ago. Since then, three groups of transmissible spongiform encephalopathies or TSE diseases have been identified in humans including familial, infectious and sporadic types. The discovery of the prion protein (PrP) in the 1980s greatly accelerated knowledge of the biology and pathogenesis of TSE diseases as this protein was found to play a critical role in disease susceptibility and the TSE species-barrier and may also be a component of the infectious agent itself. Nevertheless, the nature of the TSE agents remains an enigma. Proof of the protein-only hypothesis may require generation of biologically active transmissible agent in a cell-free environment where a virus cannot replicate. Conversely, proof of a viral aetiology will require identification and isolation of a candidate virus. Further understanding of the structure of the disease-associated protease-resistant PrP should help elucidate the mechanism of PrP conversion from the normal to the abnormal form. Such information should open up new approaches to both diagnosis and therapy.

Animals↗

Early diagnosis of lentivirus-induced infiltrative lung disease in sheep by high resolution computed tomography.

The visna-maedi lentivirus can induce an interstitial pneumonitis in sheep, and provides a convenient example to study natural or experimental lentiviral pathology. We wanted to determine whether high resolution computed tomography (HRCT) is able to detect early morphological changes following lentiviral infection in the lungs. Spontaneously infected adult sheep (n=3) and experimentally infected lambs (n=5) were compared to uninfected controls (n=4). The HRCT scans generally showed abnormal features in infected animals, including: increased parenchymal density; alveolar oedema; thickened interlobular septa; and increased density in peribronchiolar areas. HRCT was more sensitive than chest radiography for the early diagnosis of interstitial pneumonitis, although one sheep with advanced disease and radiographic and histopathological abnormalities had a paradoxically normal scan. One control animal showed minor abnormalities on scanning, which were probably due to the procedure used for anaesthesia. The HRCT observations were confirmed by postmortem histological examination of the lungs. In conclusion, high resolution computed tomography provides a noninvasive means of following the development of lung pathology in a natural ovine model of lentiviral disease.

Animals↗

The pathology of Johne's disease in sheep.

The clinical, gross and histopathological findings in 50 sheep affected with Johne's disease are described. Clinically 90% were emaciated and 20% showed severe diarrhoea. On necropsy there was thickening of the walls of the intestines, particularly of the ileum, caecum and less frequently the jejunum, but in 36% of sheep the changes were only mild. Histologically there was a granulomatous enteritis, typhlitis and colitis, with the most severe changes in the terminal ileum. High numbers of acid-fast organisms were present in the terminal ileum in over 70% of sheep. Mycobacterium paratuberculosis was cultured from only 8% of the sheep examined.

Animals↗

First report of paratuberculosis (Johne's disease) in sheep in Morocco.

Paratuberculosis (Johne's disease) was suspected in a flock of approximately 1000 sheep after weight losses and scouring had increased in adult animals despite repeated anthelmintic treatment. A total of 10 ewes showing clinical symptoms were submitted to laboratory examination. Gross pathological and histological examination of tissue samples rendered results compatible with Johne's disease in all 10 ewes. The diagnosis could only be confirmed by cultural isolation and identification of Mycobacterium paratuberculosis in the faeces of two ewes. This is considered the first documented isolation of Mycobacterium paratuberculosis in sheep in Morocco.

Animals↗