|Trujillo, Jessie - WASHINGTON STATE UNIV|
Submitted to: Animal Health and Production Compendium
Publication Type: Review Article
Publication Acceptance Date: June 22, 2005
Publication Date: June 30, 2006
Citation: Hoesing, L.M., Trujillo, J.D. 2006. CAEV Review. Animal Health and Production Compendium. ISSN 1477-2086. Interpretive Summary: Current literature is consolidated on the pathogenesis, diagnostic testing, and transmission of caprine arthritis-encephalitis virus (CAEV) in this review article. There are no known therapeutics or commercially available vaccines for CAEV infection. Control methods for CAEV have been primarily based on diagnostic testing and separation of CAEV-positive and negative goats. Currently, there is genomic evidence that CAEV and the other small ruminant lentiviruses, ovine progressive pneumonia virus (OPPV) and maedi-visna virus (MVV), can cross infect both sheep and goats naturally. Therefore, eradication of OPPV and MVV need to be also considered before implementing CAEV eradication.
Technical Abstract: Caprine arthritis-encephalitis virus (CAEV) is a small ruminant lentivirus (SRLV) in a family of retroviruses also including maedi-visna virus (MVV) and ovine progressive pneumonia virus (OPPV). SRLV infections are life long in sheep and goats and are characterized by periods of latency, followed by recrudescence of virus replication. There is no known therapeutics and no commercially available vaccines. Manifestations of clinical signs in naturally infected animals are dichotomous; where greater than 70% of animals demonstrate sub-clinical disease (non-progressor goats, NP) and 30% of animals have moderate to severe, chronic recurrent disease (progressor goats, P). Immunological control of SRLVs is associated with non-progressor status and likely dependent on various factors including SRLV strain pathogenicity and tissue/cell tropisms, immunogenetics, and environmental conditions. The original characterization of CAEV includes two primary disease manifestations: syndesmological (joint) disease (arthritic form) and neurological disease (neurological form). The joint disease form manifests as chronic recurrent arthritis of primarily the carpi (Crawford et al., 1980). Clinically affected goats (progressors) are typically juvenile or adult animals that develop moderate to severe swelling of the bursa of the extensor carpal radialis tendon with variable involvement of the radiocarpal, middle carpal and carpometacarpal joints. Advanced lesions are characterized by marked synovial membrane hyperplasia with diffuse mononuclear cell infiltrates commonly accompanied by soft tissue mineralization and osteolysis. The neurological disease form of CAEV was first clinically described and is characterized by leukoencephalomyelitis of primarily kid goats 1-5 months of age and less commonly adult goats (Cork et al., 1974; O'Sullivan et al., 1978; Norman and Smith, 1983). More recently, the reporting of neurological manifestation of CAEV, MVV and OPPV has declined which may be a reflection of virus-host adaptation or control measures aimed to reduce neonatal transmission. Other clinical manifestations of CAEV in goats can occur alone or in combination with the primary disease manifestations and include cachexia, weight loss, chronic pneumonia with dyspnea and mastitis (Phelps & Smith 1993, Ellis et al., 1988, Cork et al., 1974). Clinical signs and the detection of antibodies to CAEV in the serum typically diagnose CAEV infection. The most commonly used serological antibody detection systems include enzyme-linked immunosorbent assays (ELISA) or the agar gel immunodiffusion assay (AGID). A recently developed and validated competitive inhibition ELISA for CAEV has shown higher sensitivity than CAEV AGID (Knowles et al., 1994; Özyörük et al., 2001; Herrmann et al., 2003). As with all serological diagnostic tests, there is no such thing as 100% sensitivity and 100% specificity. Therefore, diagnosticians need to be aware of the potential for false negatives and positives. The number of false negatives depends upon the antigenic similarity of the infecting CAEV strain and the CAEV strain used in the diagnostic test. In addition, the number of false positives may depend upon the age of the animal with kids less than 1 year of age maintaining passively transferred maternal antibody. Moreover, delayed seroconversion has been reported in sheep and goats infected with SRLV. Given these issues with serological diagnostic tests, there is a need to develop and employ ancillary antemortem methods of confirming CAEV infection. Efforts to develop and validate some new tests such as PCR detection of integrated provirus and immunohistochemical detection of viral antigens will be discussed. The primary mode of transmission of CAEV is through ingestion of colostrum/ milk following birth (Adams et al., 1983), however horizontal transmission between adult goats has been reported (Rowe et al., 1992a). The relative contribution of NP and P goats to transmission of CAEV is not known. However, it is generally believed that both groups of CAEV infected goats serve as potential reservoirs of CAEV. Therefore, control measures include 1) serologic testing of adult goats and separation or elimination of seropositive animals and 2) heat inactivation of colostrum or milk (56ºC for 1 hour) from CAEV positive nannies.