Visna virus

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colspan=2 style="text-align: center; background-color: rgb(250,250,190)" | Visna virus
colspan=2 style="min-width:15em; text-align: center; background-color: rgb(250,250,190)" | Virus classification
Species	''Visna/maedi virus''

The Visna virus is a member of the Lentivirus genus within the Retroviridae family. It is a slow virus that causes progressive neurological disease in sheep, known as Visna, and a respiratory condition called Maedi. The virus is closely related to the Human Immunodeficiency Virus (HIV), which causes AIDS in humans, and is used as a model to study lentiviral infections.

History

The Visna virus was first identified in Iceland in the 1930s, where it caused significant economic losses in the sheep industry. The name "Visna" means "wasting" in Icelandic, reflecting the debilitating nature of the disease. The virus was isolated in the 1950s, and subsequent research has provided insights into its pathogenesis and relationship to other lentiviruses.

Virology

Visna virus is an enveloped virus with a single-stranded RNA genome. Like other retroviruses, it replicates through a DNA intermediate using the enzyme reverse transcriptase. The virus integrates into the host cell's genome, leading to persistent infection. The genome of Visna virus encodes several structural proteins, including the envelope protein, which is crucial for viral entry into host cells.

Pathogenesis

The Visna virus primarily infects macrophages and monocytes, cells of the immune system. The infection leads to chronic inflammation and demyelination in the central nervous system, resulting in the neurological symptoms characteristic of Visna. In the lungs, the virus causes interstitial pneumonia, known as Maedi, characterized by progressive respiratory distress.

Clinical Manifestations

Infected sheep may exhibit a range of symptoms depending on the form of the disease. Visna is characterized by ataxia, weakness, and paralysis, while Maedi presents with coughing, nasal discharge, and labored breathing. The disease is progressive and ultimately fatal.

Diagnosis

Diagnosis of Visna virus infection is based on clinical signs, serological tests, and detection of viral RNA by polymerase chain reaction (PCR). Histopathological examination of affected tissues can also aid in diagnosis.

Prevention and Control

There is no vaccine for Visna virus, and control measures focus on preventing the spread of infection. This includes culling infected animals, implementing biosecurity measures, and maintaining closed flocks to prevent introduction of the virus.

Research and Significance

Visna virus serves as an important model for studying lentiviral infections, including HIV. Research on Visna virus has contributed to understanding viral pathogenesis, immune evasion, and potential therapeutic strategies for lentiviral diseases.

Also see

• Lentivirus
• Retrovirus
• Human Immunodeficiency Virus (HIV)
• Maedi-Visna
• Sheep diseases