Caprine arthritis/encephalitis

Most infected goats stay clinically normal. In kids under about six months, the neurological form begins as hind-limb weakness and incoordination and progresses to paralysis. In adults, the usual picture is chronic arthritis: stiffness, lameness, swollen joints, reluctance to rise and walking on the knees, with weight loss. Does may develop a firm, swollen udder with low milk output. Some adults show cough and laboured breathing from interstitial pneumonia. Signs develop over months to years.

Caprine arthritis/encephalitis is caused by caprine arthritis encephalitis virus, a small ruminant lentivirus (family Retroviridae) closely related to maedi-visna virus of sheep. The virus targets cells of the monocyte/macrophage lineage and integrates into host DNA, so infection is lifelong despite a vigorous immune response. It stays largely silent in circulating monocytes; viral expression switches on as those cells mature into macrophages inside tissues. The result is slow, progressive inflammation with mononuclear cell infiltration in the joints, udder, lungs and central nervous system, giving four clinical pictures: encephalomyelitis, polyarthritis, indurative mastitis and interstitial pneumonia. There is a long eclipse phase before any signs appear.

Goats are the main host, and the virus also infects sheep. Colostrum and milk are the principal route in goats; virus is also present in respiratory secretions, lung fluids and faeces, and infection can pass by close contact, in utero, venereally, and on shared needles, ear-tagging and dehorning equipment. Symptomatic and asymptomatic carriers both shed virus, and most infected animals never show signs. Distribution is highest in industrialised countries and followed the international movement of European dairy goat breeds. In western Iran, a PCR survey found 17% of goats infected (27% in Kurdistan province) and 13 of 15 farms affected, with no seasonal pattern. It is not zoonotic and is a WOAH-listed disease.

Joints, mammary gland, lungs, central nervous system (brain and spinal cord), monocyte/macrophage system

Test and cull; quarantine and test new animals twice at least 60 days apart; pasteurised colostrum and milk for kids; sterilise needles and dehorning equipment; artificial insemination; strict biosecurity.

No treatment and no vaccine. Infection is lifelong, and goats that develop clinical disease do not recover; care is supportive only, and the disease is ultimately fatal.