Sheep Pulmonary Adenomatosis

Also known as: Jaagsiekte (driving sickness in Afrikaans) — Pulmonary Carcinomatosis — Ovine Pulmonary Carcinoma — OPC — SPA

Introduction

This is a progressive disease in sheep caused by the Retrovirus family. The virus causes an infectious, bronchiolar-alveolar lung tumour of sheep. This is the virus that killed Dolly, the famous cloned ewe, at 6 years old. The virus works by causing a proliferation of the alveolar lining cells in the lungs, causing mass amounts of fluid to be produced. The proliferative foci project into the alveoli and bronchi and then form slow-growing tumours with death at 3-4 years of age or older.

The virus is found in Europe, Africa and the Americas. It is found in around 25% of cases of pneumonia in sheep in Scotland and is prevalent throughout the rest of the British Isles. It is absent from the United States. The virus is found to be commonest under intensive management systems, which favour aerosol and close contact transmission of disease.

Signalment

All sheep are affected but Merino sheep are found to be the most at risk. Sheep are generally 3 - 4 years of age or older when clinical signs first appear.

Clinical Signs

Low exercise tolerance, gradual weight loss, dyspnoea, coughing and the presence of nasal discharges, bilaterally. Secondary bacterial infection by Pasteurella haemolytica often precipitates death.

Diagnosis

Clinical signs plus the age of the sheep can often be indicative of the disease. Differential diagnoses include chronic progressive pneumonia (maedi - lentivirus causing lymphofollicular interstitial pneumonia with little to no significant alveolar epithelial hyperplasia). Also bacterial bronchopneumonias and verminous pneumonias may be present in addition to OPC.

A 'wheelbarrow test', where the sheep is lifted by its hind legs so its head drops down can be used to detect any nasal discharge seeping out when the test is performed.

Pathology

At post mortem the tumour is fawn-grey in colour but may be obscured by autolysis or pneumonia. The lungs will appear heavy and fail to collapse. The cut surface will ooze fluid and there is often secondary bacterial infection present concurrently. There may occasionally be metastasis to bronchial and mediastinal lymph nodes. There may also be right ventricular dilation and hypertrophy.

The virus cannot be grown in cultures, but it can be seen on electron microscopy of tumour cells of infected sheep. Multiple proliferative foci of cuboidal or columnar cells which line alveoli and form papillary projections into their lumina (i.e., adenomatous hyperplasia, adenomas and adenocarcinomas). In larger masses the pattern is obscured and fibroplasia often occurs in more disorganized and degenerative areas. Early or uncomplicated lesions may have little to no accumulation of inflammatory cells; however, there are usually low to moderate aggregations of alveolar macrophages in alveolar lumina. PCR on blood is being developed at Moredun.

Control

All affected animals should be culled. There is no vaccine to the disease, as the disease is progressive and no specific antibodies have yet been detected.

References

Dungworth DL: The Respiratory System, In:Pathology of Domestic Animals, 4th edition, ed. Jubb KVF, Kennedy PC, and Palmer N, pp.690-2, Academic Press, San Diego, CA, 1993.

Fenner FJ, Gibbs EPJ, Murphy FA, Rott R, Studdert MJ, and White DO: Retroviridae, In: Veterinary Virology, 2nd edition, pp. 578-9, Academic Press, Inc., San Diego CA, 1993.

Hecht SJ, Sharp JM, and Demartini JC: Retroviral Aetiopathogenesis of Ovine Pulmonary Carcinoma: A Critical Appraisal. Br Vet J (1996) 152:395-406.

Kimberling CV: Diseases of Adult Sheep, In: Jensen and Swift’s Diseases of Sheep, 3rd edition, pp. 270-3, 1988.

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