Signalment:  

1-year-old intact female Rocky Mountain goat (Oreamnos americanus) This goat exhibited 3 months of progressive respiratory difficulty that was unresponsive to antibiotic therapy, leading to euthanasia. She was one of a small group (approximately 25) of captive bred Rocky Mountain goats at a private facility. This animal and several others were raised on raw goats milk obtained from a local dairy goat farm. At the time the animals were raised the dairy goat farm was believed to be free of caprine arthritis encephalitis virus (CAEV), but CAEV was subsequently confirmed on the premises. A 2-year-old mountain goat that had received the raw goats milk from the same dairy was euthanized approximately 1 month later due to progressive weight loss, dyspnea, and recent onset of left sided spastic hemiparesis. Pulmonary lesions were similar in this second animal, and in addition there was a locally extensive unilateral nonsuppurative inflammatory and demyelinating lesion within the cranial cervical spinal cord.


Gross Description:  

Postmortem was performed approximately 24 hours following euthanasia. The animal was in thin body condition. The lungs failed to collapse and were diffusely dark red, firm, and meaty. Pulmonary lymph nodes were moderately enlarged. There were no other significant gross findings.


Histopathologic Description:

Slides from two different blocks are submitted. Both exhibit similar changes. There is severe diffuse interstitial fibrosis with priminent perivascular and peribronchiolar lymphoid aggregates. There is diffuse type II pneumocyte hyperplasia, although many cells have sloughed due to postmortem artifact. Alveoli contain protein, often in aggregates, and many prominent macrophages. Smooth muscle associated with terminal bronchioles is hyperplastic. One section contains a locally extensive zone of intrabronchial necrotic debris.


Morphologic Diagnosis:  

Lung: Severe diffuse chronic interstitial pneumonia with lymphoid hyperplasia consistent with Caprine Arthritis Encephalitis Virus (CAEV) infection


Lab Results:  

Escherichia coli isolated from lung and pulmonary lymph node. No mycoplasma isolated from lung or pulmonary lymph node. Fluorescent antibody testing of lung and pulmonary lymph node was negative for IBR and BVD viruses.


Condition:  

Small ruminant lentivirus; CAEV


Contributor Comment:  

The history of progressive dyspnea associated with weight loss and the histopathologic lesions within the lung are characteristic of pulmonary disease due to CAEV infection. It should be noted, however, that the severe interstitial fibrosis in this case is somewhat unusual (1). Secondary infection by E. coli is suspected.

CAEV is one of a family of small ruminant lentiviruses (SRLV) that cause chronic inflammatory disease in goats (genus Capra, subfamily Caprinae, family Bovidae) and sheep (genus Ovis, subfamily Caprinae, family Bovidae). Viral integration into host DNA causes persistent infection, primarily of monocytes, macrophages, and dendritic cells (2,4). Mammary gland involvement is common, and infection is most often due to ingestion of milk from infected dams. Infection from direct contact is also possible, but is less common. Experimental infection of Mouflon-domestic sheep hybrids by CAEV has been reported (3). Recent phylogenetic studies have identified multiple subgroups of SRLV. One group, SRLV subtype A4, has been found to be directly transmissible and interchangeable between goats and sheep(5).

This is the first known instance of disease compatible with CAEV occurring in a Rocky Mountain goat (genus Oreamnos, subfamily Caprinae, family Bovidae). No involvement of joints or mammary gland were identified in these two cases. Neurologic disease due to CAEV is most common in goats 2-4 months of age, but sporadic cases occur in adults (6). Although immunohistochemical confirmation of CAEV was still in progress at the time of submission, various factors strongly suggest CAEV as the cause of infection in this and the second affected Rocky Mountain goat. The histopathologic lesion of diffuse interstitial pneumonia with type II hyperplasia and lymphoid hyperplasia are characteristic of pulmonary lentivirus infection (1). Although infection by another member of the SRLV family cannot be ruled out in this case based on findings to date, the history of ingestion of raw goats milk from a CAEV positive herd, and the characteristic locally extensive demyelinating myelitis in the second goat (as opposed to the more diffuse and strongly periventricular spinal cord lesions of maidi-visna virus)(6)) strongly suggest CAEV infection in this captive bred Mountain goat.


JPC Diagnosis:  

Lung: Pneumonia, interstitial, chronic, diffuse, moderate, with marked interstitial fibrosis, lymphoid hyperplasia, and type II pneumocyte hyperplasia.


Conference Comment:  

Slide variability included multifocal areas of acute neutrophilic alveolitis likely due to secondary bacterial infection. However, no organisms were seen. 

Small ruminant lentiviruses (SRL), in the family Retroviridae, include the closely related maedi-visna virus (ovine progressive pneumina) and caprine arthritis encephalitis Virus. The viral gene of lentiviruses is a single-stranded RNA and encodes for various genes, including:1


Infection with CAEV results in two main manifestations of the disease: slowly progressive arthritis in adult goats and more acute neurologic disease in kids 2-4 months old.1 The arthritic lesions tend to localize within the carpus, but the tarsus, fetlock, stifle, and atlanto-occipital joint can be affected as well. Neurologic signs are variable and include encephalitis, progressive ataxia and weakness. Pneumonia occurs less frequently but can be the main presenting feature or occur in combination with the joint or neurologic lesions. The distinctive pulmonary lesion includes alveoli filled with densely eosinophilic fluid, type II pneumocyte hyperplasia, and alveolar septa thickened by lymphocytes. Type II pneumocyte hyperplasia is not a prominent feature in the pneumonia of ovine progressive pneumonia.1

In contrast to other lentiviruses in animals (including the various species specific immunodeficiency viruses of simians, humans, felines, and bovines), the SRLs do not cause immunosuppression as a primary feature. However, secondary bacterial infection by Pasteurella multocida or Arcanobacterium pyogenes, as well as parasitic infection by Dictyocaulus sp. or Protostrongylus sp., can commonly be seen in association with SRL infection.1


References:

1. Caswell JL, Williams KJ: Respiratory system. In: Jubb, Kennedy, and Palmers Pathology of Domestic Animals, ed. Maxie MG, 4th ed., vol. 2, pp. 618-620. Elsevier Limited, St. Louis, MO, 2007
2. Guiguen F, Mselli-Lakhal L, Durand J, Du J, Favier C, Fornazero C, Grezel D, Balleydier S, Hausmann E, Chebloune Y: Experimetnal infection of Mouflon-domestic sheep hybrids with caprine arthritis-encephalitis virus. Am J Vet Res 61:456-461, 2000
3. H+�-�tzel I, Cheevers WP: Host range of small-ruminant lentivirus cytopathic variants determined with a selectable caprine arthritis-encephalitis virus pseudotype system. J Virol 75:7384-7391, 2001
4. Mdurvwa EG, Ogunbiyi PO, Gakou HS, Reddy PG: Pathogenic mechanisms of caprine arthritis-encephalitis virus. Vet Res Commun 18:483-490, 1994
5. Shah C, Huder JB, Boni J, Schonmann M, Muhlherr J, Lutz H, Schupbach J: Direct evidence for natural transmission of small-ruminant lentiviruses of subtype A4 from goats to sheep and vice versa. Virol 78:7518-7522, 2004
6. Summers BA, Cummings JF, de Lahunta A: Veterinary Neuropathology, pp. 128-132. Mosby, St. Louis, MO, 1995

A virtual slide is not available for this case.


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