Caprine Arthritis And Encephalitis - Generalized Conditions

Caprine arthritis encephalitis virus is an enveloped, single-stranded RNA lentivirus in the family Retroviridae. There are several genetically distinct isolates of the virus that differ in virulence.

This virus is closely related to the ovine lentiviruses that cause ovine progressive pneumonia and maedi-visna in North America and Europe, respectively. Cross-species transmission is possible via feeding of infected milk and colostrum. Therefore, the ovine and caprine lentiviruses are commonly referred to as small ruminant lentiviruses.

CAEV infection is widespread in dairy goat breeds but uncommon in meat- and fiber-producing goats. This distinction has been attributed to genetic factors, management practices such as feeding colostrum and milk from a single dam to multiple kids, and farming practices in high-income countries (eg, frequent introductions of new animals into a herd). Prevalence of infection increases with age but is apparently not influenced by sex. Most goats are infected at an early age, remain seropositive for life, and may develop signs of disease months to years after infection.

The chief mode of spread of CAEV is via ingestion of virus-infected colostrum or milk by kids. The feeding of pooled colostrum or milk to kids is a particularly risky practice, because a few infected does will spread the virus to a large number of kids. Horizontal transmission also contributes to disease spread within herds and may occur through direct contact, exposure to fomites at feed bunks and waterers, ingestion of contaminated milk in milking parlors, or serial use of needles or equipment contaminated with blood. Unlikely methods of transmission, as indicated by results of experimental studies, include in utero transmission to the fetus, infection of the kid during parturition, and infection via natural breeding or embryo transfer.

The pathogenesis of CAE is not fully understood. Virus-infected macrophages in colostrum and milk are absorbed intact through the gastrointestinal mucosa. Infection is subsequently spread throughout the body via infected mononuclear cells. Periodic viral replication and macrophage maturation induce characteristic lymphoproliferative lesions in target tissues and organs such as the lungs, synovium, choroid plexus, and udder. Persistence of CAEV in the host is facilitated by its ability to become sequestered as provirus in host cells. Infection induces strong humoral and cell-mediated immune responses, but neither response is protective.