Humoral immune response to caprine arthritis-encephalitis virus in goat herds

Caprine arthritis-encephalitis (CAE) is an infectious contagious disease of goats caused by single-stranded RNA virus belonging to the family Retroviridae genus Lentivirus [1]. Caprine arthritis-encephalitis virus infects monocytes where, thanks to the enzyme – reverse transcriptase – it changes into DNA provirus and becomes integrated into the host genome [2]. Such latent infection is life-long and persists despite vigorous humoral immune response mounted by the host usually in 2 to 8 weeks after infection. Intensively produced neutralizing antibodies are incapable of eliminating the virus although they markedly reduce its load. The virus is able to evade the humoral immune response by making various antigenic variants of itself [3]. Infected monocytes migrate to the various tissues, mainly synovium, lung, udder and central nervous system where they differentiate into macrophages. Caprine arthritisencephalitis virus replication takes place exclusively at this moment. Infected macrophages secrete inflammatory cytokines which attract lymphocytes and induce chronic immune-mediated inflammation in infected tissues [4, 5]. As it is a very slow process, the disease develops slowly with clinical manifestation not sooner than 12 months after infection [6]. By now no cases in which goats have cleared the infection have been reported, which is consistent with observations in other lentiviral infections in animals [7]. Therefore humoral immune response is rather the hallmark of the life-long infection than of any protective value. Caprine arthritis-encephalitis was first described in the United States, in 1974 [8]. Even though the neurologic form was the manifestation primarily reported, it soon turned out that four other clinical presentations – polyarthritis, induration of the udder with hypogalactia, chronic interstitial pneumonia and wasting syndrome – can also be encountered, with chronic progressive polyarthritis being the most common [9]. By now CAE has been reported from all over the world [10] with confirmation in Poland in 1996 [11]. The objective of the study was to evaluate humoral immune response to CAEV infection in goat herds. Abstract The serological study was performed to assess the humoral immune response to caprine arthritisencephalitis virus infection in goat herds. The collection of 1074 sera harvested in 76 randomly selected breeding herds was tested using commercial ELISA test. Positive and inconclusive results were verified with AGID test. As serial mode of testing was applied, only these sera which turned out positive in the latter test were classified truly positive. Eventually, 161 goats (15.0%) produced humoral immune response to CAEV. They originated from 20 (26.3%) herds. Within-herd prevalence rate of caprine arthritisencephalitis CAE ranged from 4.2 to 80.0% with a median 33.3%. The prevalence of CAE was lowest (16.5%) in young goats and highest (55.7%) in a group of four year-old goats. The results of our investigation indicate that CAEV infection tends to spread slowly within a goat herd but eventually the seroprevalence can reach such high values that the only way to eradicate the disease is to cull the entire herd. That shows the importance of early detection of CAE in a herd which allows eradication of the disease by culling only seropositive animals.