Caprine Arthritis and Encephalitis

Caprine Arthritis and Encephalitis (CAE) virus is widespread in dairy goats but uncommon in meat and fibre-producing goats. Goats usually get infected as kids through virus-infected colostrum or milk. Horizontal transfer can also occur.

Once infected, goats remain virus positive for life, and the disease may manifest months or years later. Only about 20 % of CAE virus infected goats display clinical signs during their lifetime. CAE most commonly manifests as polyarthritis in adult goats, but may less commonly present as pneumonia, encephalitis, or mastitis.

Arthritis is the most common form of CAE. Adult goats will exhibit a swelling of one or both carpal joints (hence the name “big knee”). It may extend above the knee when the tendons are affected. The stifle, coxofemoral, atlanto- occipital, and hock joints are also potential locations. The swellings are usually soft but can progress to hard masses. The presence of lameness is variable but usually progressive. Some animals can have significant lameness. Goats may also present with illthrift and poor hair coats.

The encephalitis form rarely presents in adult goats; it is generally seen in kids 2-4 months old. This form presents as ascending paresis or paralysis, and can be accompanied by urinary retention and bloating when severe. The pulmonary form of CAE presents as chronic interstitial pneumonia which can appear clinically similar to the pulmonary form of caseous lymphadenitis. The “hard udder” syndrome in lactating animals presents only as a firm udder and reduced milk production.

Diagnosis is usually by clinical signs and history, but definitive diagnosis requires biopsy or necropsy samples, chilled for virus isolation, and in formalin for histology. Serological testing can aid in diagnosis and is also used in prevention; ELISA is the most accurate test. Differential diagnoses for arthritis in goats are traumatic arthritis or infectious arthritis caused by Mycoplasma sp.