Visna virus
| Visna virus | |
|---|---|
| Virus classification | |
| Group: | Group VI (ssRNA-RT) |
| Order: | Unassigned |
| Family: | Retroviridae |
| Subfamily: | Orthoretrovirinae |
| Genus: | Lentivirus |
| Species: | Visna virus |
| Synonyms | |
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Visna virus (also known as visna-maedi virus, maedi-visna virus and ovine lentivirus) from the genus Lentivirus and subfamily Orthoretrovirinae, is a "prototype"retrovirus that causes encephalitis and chronic pneumonitis in sheep. It is known as visna when found in the brain, and maedi when infecting the lungs. Lifelong, persistent infections in sheep occur in the lungs, lymph nodes, spleen, joints, central nervous system, and mammary glands; The condition is sometimes known as "ovine progressive pneumonia" (OPP), particularly in the United States, or "Montana sheep disease".White blood cells of the monocyte/macrophage lineage are the main target of visna virus.
First described in 1954 by Bjorn Sigurdsson in Iceland, Maedi-visna virus was the first lentivirus to be isolated and characterized, accomplished in 1957 by Sigurdsson. "Maedi" (Icelandic for dyspnoea) and "visna" (Icelandic for "wasting" or "shrinking" of the spinal cord) refer to endemic sheep herd conditions that were only found to be related after Sigurdsson's work.
Visna infection may progress to total paralysis leading to death via inanition; however, if given assistance in eating and drinking, infected animals may survive for long periods of time, sometimes greater than ten years. Viral replication is almost exclusively associated with macrophages in infected tissues; however, replication is restricted in these cells—that is, the majority of cells containing viral RNA do not produce infectious virus.
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