Caprine Arthritis Encephalitis Virus

Introduction

This disease is caused by a virus from the family retrovirus (lentivirus) and is serologically related to Maedi-Visna virus described in sheep. They have different antigenic and genetic envelopes. This virus affects goats only.

The disease is characterised by an immune complex induced by T cells. Transfer is by milk and colostrum, particularly batch mixing from antibody positive dams. The disease is present in roughly 10% of UK herds, however clinical disease is rare.

Signalment

Goats contract the disease as kids, but clinical disease can be seen then, or in adults.

Clinical Signs

There are two forms that the disease can take, depending on the age of the animal. In kids a non-suppurative leukoencephalomyelitis occurs, whereas in adult goats chronic, non-suppurative arthritis occurs. The virus also causes interstitial pneumonia which tends to be obscured by other clinical signs.

Diagnosis

In older goats where pantropic arthritis occurs, this disease is usually suspected.

The Visna-Maedi serology (ELISA) test can be used to remove positive stock.

Post mortem examination can be performed. Signs characteristic of the disease include firm lungs, especially caudal lobes, pink-grey focal lesions are found here. On micro-pathology there will be a thickened alveolar wall, lymphocyte infiltration and type II pneumocyte hyperplasia is also seen. This can be confused with or coexisting with parasitic pneumonia. In limbs, large limb joints are thickened and carpal hygroma is often present. There will also be cystic swelling on the cranial surface of the knee containing serous fluid. In advanced cases synovial fluid hypertrophy, necrosis, mineralisation and articular cartilage formation will be seen.

Control

In herds where the virus is known to exist, separate kids from virus positive mothers at birth and do not allow them to suckle. The mothers' colostrum can be treated (56 deg for 1 hour) OR rear the kids on artificial milk.

References

Blood, D.C. and Studdert, V. P. (1999) Saunders Comprehensive Veterinary Dictionary (2nd Edition), Elsevier Science

Bridger J and Russell, P (2007) Virology Study Guide, Royal Veterinary College

Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition), Merial

Radostits, O.M, Arundel, J.H, and Gay, C.C. (2000) Veterinary Medicine: a textbook of the diseases of cattle, sheep, pigs, goats and horses, Elsevier Health Sciences