Maedi-Visna virus: current perspectives

Abstract

Maedi-Visna virus (MVV) and caprine arthritis-encephalitis virus are commonly known as small ruminant lentiviruses (SRLVs) due to their genetic, structural, and pathogenic similarities. They produce lifelong lasting infections in their hosts, which are characterized by slow progression till overt disease happens. There are four major clinical forms derived from a chronic inflammatory response due to the constant low grade production of viruses from monocyte-derived macrophages: respiratory (caused by interstitial pneumonia), mammary (which may produce a decrease in milk production due to subclinical mastitis), joint (characterized by lameness), and neurological (characterized by chronic nonpurulent meningoencephalomyelitis). There are three levels which try to eliminate the virus: cellular, body, and the flock level. However, SRLVs have ways to counteract these defenses. This review examines some of them.

Etiology, Epizootiology and Control of Maedi-Visna in Dairy Sheep: A Review

“…There is a continuous effort for the identification and classification of SRLVs strains due to large genetic diversity of the isolated viruses [17,29]. To date, five strain groups, namely, A, B, C, D, and E with their subtypes have been identified in sheep and goats [1,18]. Group A consists of MVV strains and has 15 subtypes, group B consists of CAEV strains with 3 subtypes, whereas, the other three groups refer to strains which have been isolated from Norway (group C), Spain and Switzerland (group D), and Italy (group E) [18].…”

“…To date, five strain groups, namely, A, B, C, D, and E with their subtypes have been identified in sheep and goats [1,18]. Group A consists of MVV strains and has 15 subtypes, group B consists of CAEV strains with 3 subtypes, whereas, the other three groups refer to strains which have been isolated from Norway (group C), Spain and Switzerland (group D), and Italy (group E) [18]. Some of the classical strains with known sequences are the K1514 (Iceland) and its neurovirulent clones KV1772-kv72/67 and LV1-1KS1, SA-OMVV (South Africa), EV1 (UK), and P1OLV (Portugal).…”

“…Immunosuppression of animals due to aging, co-existing of diseases and environmental stressors accelerates virus replication and clinical evidence of the disease becomes apparent. At the flock-level, serum detection of antibodies, the severity of clinical disease and the number of deaths/culled animals, can be affected by management practices and the co-existence of other diseases [18].…”

“…However, many animals infected with the virus remain undiagnosed due to the late (from a few months to three years) seroconversion [13,14]. In the past, several papers have reviewed the status of MV in sheep industry [5,6,[15][16][17][18][19][20][21][22]; nevertheless, the objectives of this review paper are to summarize and provide an integrated overview of the current knowledge regarding the epizootiology and control strategies of MV in dairy sheep, to describe the research framework and to cover existing gaps in understanding future challenges regarding MV.…”

Serological Results of MVV and Caev Antibodies in Samples Collected From Sheep and Goat Flocks of Romania

“…Some susceptible animals do not express any clinical sign following the viral exposure, but some could exhibit a respiratory form with interstitial pneumonia (Maedi) or a neurological form with progressive inflammatory disease of the central nervous system (Visna). Also, sheep and goats could be affected by inflammatory processes (located in joints and/or mammary gland) (Grego et al, 2007;Gomez-Lucia et al, 2018). The clinical signs are: coughing, lameness, weight loss and failures to mount (Hamza & Ozkan, 2017).…”