CASE REPORT
Maedi-visna Virus Infection in Rams in Nova Scotia R. G. STEVENSON*
Introduction In 1971, formalin-fixed lung tissue from a five year old Dorset X Leicester ewe suspected of having progressive interstitial pneumonia was forwarded to this laboratory from Rock Forest, Quebec (R. Bellavance, Personal Cummunication). Histopathological examination confirmed the tentative diagnosis of chronic interstitial pneumonia resembling Montana progressive pneumonia (12). Bellavance and Phaneuf (2) and Bellavance et al (3) subsequently reported the presence of serum neutralizing antibody titres to maedi-visna virus of up to 1:128 in adult sheep from the affected flock in Quebec. This report describes two cases of chronic interstitial pneumonia and encephalomyelitis in rams which had originally come from the same flock as those reported by Bellavance et al (3). History In December, 1972, a live Dorset X Leicester ram (72) was submitted to this laboratory for necropsy. It had originated in an experimental flock in the Province of Quebec, and had been brought to another institutional flock in Nova Scotia in 1972. On November 1, 1972 as a yearling, it had been turned out with a group of ewes. Several weeks later, the ram was noticed to be circling in either direction and staggering. It then became recumbent but continued to eat. Further submissions were not received until February 25, 1974 when the head and lungs of another Dorset X Leicester ram (741) from the same premises were submitted. This ram originated in the same flock as ram 72. Clinical signs, as reported by the shepherd, included deviation of the head and circling which had been going on for approximately four weeks. The ram had been treated with a broad spectrum antibiotic but there was no improvement and the animal was euthanized. Macroscopic Examination In ram 72, thick-walled abscesses in the left
retropharyngeal and mediastinal lymph nodes and throughout the enlarged lungs were the only abnormalities noted. In ram 741, the lungs were larger than normal and contained several small, thick-walled abscesses and, in addition, there was one large abscess in the left cardiac lobe. Gross abnormalities were not observed in the brain. Bacteriology Smears from the pulmonary abscesses revealed the presence of numerous Gram-positive pleomorphic rods suggestive of Corynebacterium spp. but routine culture on blood agar, MacConkey and triple sugar iron agar plates and in thioglycollate and Robertson's meat broths was negative for bacteria. Histopathology Significant lesions were confined to the lungs and central nervous system (CNS) and were similar in both rams. In the lungs, the most striking features were lymphoid hyperplasia, smooth muscle hypertrophy and interstitial pneumonia. Accumulations of lymphocytes, associated with bronchi, bronchioles and blood vessels (Figure 1), for the
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-- r- h 3 M. 1~~~~ FIGURE 1. Marked lymphoid hyperplasia and interstitial pneumonia. H & E. x 32.
*Animal Pathology Division, Health of Animals Branch, Agriculture Canada, Atlantic Area Laboratory, P.O. Box 1410, Sackville, New Brunswick EOA 3CO Can. vet. J. 19: 159-163 (June 1978)
most part formed follicles with the germinal centers containing a few necrotic cells and mitotic
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figures. Accumulations about small blood vessels and bronchioles were most pronounced, and often tended to form complete cuffs along the length of the vessel or airway. Occasionally, lymphoid follicles seemed not be related to either bronchioles or blood vessels. Bronchi and bronchioles were normal except for some lymphocytic infiltration of the mucosa in a few airways. There was hypertrophy of the smooth muscle. surrounding smaller bronchioles, which became more pronounced at the level of alveolar ducts and alveoli (Figure 2). In the latter sites, the hypertrophy was very conspicuous but did not uniformly involve the whole lung. Fibrosis was minimal except in areas where abscesses were present. Interalveolar septa were thickened due to accumulations of mononuclear cells. Some of these cells were lymphocytes but most were cells with larger paler nuclei. Occasionally, alveoli contained macrophages and in some areas there was pseudo-epithelialization of alveoli. Adenomatous foci were not observed. Atelectasis was confined to alveoli in the immediate vicinity of abscesses. Inclusions were not observed in epithelial cells or macrophages.
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FIGURE 3. Perivascular lymphocytic cuffing and increased numbers of microglia in the cerebellum. H & E. x 32.
Lesions in the spinal cord of the one ram examined were minimal and consisted of perivascular cuffing in the ventral horn of C5 and one focus of gliosis in the adjacent white matter. Generally, lesions in both brains could be classified in the following manner: a) Severe - Medulla oblongata - Pons - Cerebellum b b) Moderate - Area of the thalamus c) Mild or Absent - Cerebrum In the medulla and pons there was marked 4C i_: _F infiltration of the Virchow-Robin perivascular increased numbers of oligodendroglia and * --= xwspace, microglia, sometimes forming glial nodes, and in sections stained with luxol fast blue, demyelina*
Maedi-visna Virus Infection in Rams in Nova Scotia R. G. STEVENSON*
Introduction In 1971, formalin-fixed lung tissue from a five year old Dorset X Leicester ewe suspected of having progressive interstitial pneumonia was forwarded to this laboratory from Rock Forest, Quebec (R. Bellavance, Personal Cummunication). Histopathological examination confirmed the tentative diagnosis of chronic interstitial pneumonia resembling Montana progressive pneumonia (12). Bellavance and Phaneuf (2) and Bellavance et al (3) subsequently reported the presence of serum neutralizing antibody titres to maedi-visna virus of up to 1:128 in adult sheep from the affected flock in Quebec. This report describes two cases of chronic interstitial pneumonia and encephalomyelitis in rams which had originally come from the same flock as those reported by Bellavance et al (3). History In December, 1972, a live Dorset X Leicester ram (72) was submitted to this laboratory for necropsy. It had originated in an experimental flock in the Province of Quebec, and had been brought to another institutional flock in Nova Scotia in 1972. On November 1, 1972 as a yearling, it had been turned out with a group of ewes. Several weeks later, the ram was noticed to be circling in either direction and staggering. It then became recumbent but continued to eat. Further submissions were not received until February 25, 1974 when the head and lungs of another Dorset X Leicester ram (741) from the same premises were submitted. This ram originated in the same flock as ram 72. Clinical signs, as reported by the shepherd, included deviation of the head and circling which had been going on for approximately four weeks. The ram had been treated with a broad spectrum antibiotic but there was no improvement and the animal was euthanized. Macroscopic Examination In ram 72, thick-walled abscesses in the left
retropharyngeal and mediastinal lymph nodes and throughout the enlarged lungs were the only abnormalities noted. In ram 741, the lungs were larger than normal and contained several small, thick-walled abscesses and, in addition, there was one large abscess in the left cardiac lobe. Gross abnormalities were not observed in the brain. Bacteriology Smears from the pulmonary abscesses revealed the presence of numerous Gram-positive pleomorphic rods suggestive of Corynebacterium spp. but routine culture on blood agar, MacConkey and triple sugar iron agar plates and in thioglycollate and Robertson's meat broths was negative for bacteria. Histopathology Significant lesions were confined to the lungs and central nervous system (CNS) and were similar in both rams. In the lungs, the most striking features were lymphoid hyperplasia, smooth muscle hypertrophy and interstitial pneumonia. Accumulations of lymphocytes, associated with bronchi, bronchioles and blood vessels (Figure 1), for the
t_
, .
.~~~~~~.
-- r- h 3 M. 1~~~~ FIGURE 1. Marked lymphoid hyperplasia and interstitial pneumonia. H & E. x 32.
*Animal Pathology Division, Health of Animals Branch, Agriculture Canada, Atlantic Area Laboratory, P.O. Box 1410, Sackville, New Brunswick EOA 3CO Can. vet. J. 19: 159-163 (June 1978)
most part formed follicles with the germinal centers containing a few necrotic cells and mitotic
.Z.}.
figures. Accumulations about small blood vessels and bronchioles were most pronounced, and often tended to form complete cuffs along the length of the vessel or airway. Occasionally, lymphoid follicles seemed not be related to either bronchioles or blood vessels. Bronchi and bronchioles were normal except for some lymphocytic infiltration of the mucosa in a few airways. There was hypertrophy of the smooth muscle. surrounding smaller bronchioles, which became more pronounced at the level of alveolar ducts and alveoli (Figure 2). In the latter sites, the hypertrophy was very conspicuous but did not uniformly involve the whole lung. Fibrosis was minimal except in areas where abscesses were present. Interalveolar septa were thickened due to accumulations of mononuclear cells. Some of these cells were lymphocytes but most were cells with larger paler nuclei. Occasionally, alveoli contained macrophages and in some areas there was pseudo-epithelialization of alveoli. Adenomatous foci were not observed. Atelectasis was confined to alveoli in the immediate vicinity of abscesses. Inclusions were not observed in epithelial cells or macrophages.
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FIGURE 3. Perivascular lymphocytic cuffing and increased numbers of microglia in the cerebellum. H & E. x 32.
Lesions in the spinal cord of the one ram examined were minimal and consisted of perivascular cuffing in the ventral horn of C5 and one focus of gliosis in the adjacent white matter. Generally, lesions in both brains could be classified in the following manner: a) Severe - Medulla oblongata - Pons - Cerebellum b b) Moderate - Area of the thalamus c) Mild or Absent - Cerebrum In the medulla and pons there was marked 4C i_: _F infiltration of the Virchow-Robin perivascular increased numbers of oligodendroglia and * --= xwspace, microglia, sometimes forming glial nodes, and in sections stained with luxol fast blue, demyelina*
