Pathogenesis of maedi-visna.

Area of Science:

• Veterinary Virology
• Pathology
• Immunology

Background:

• Maedi-visna virus (MVV) infection in sheep typically presents as a subclinical, persistent carrier state.
• In high-prevalence flocks, MVV causes significant economic losses, primarily through ill-thrift and chronic respiratory disease (maedi) in adult ewes.
• Other manifestations include indurative mastitis affecting lamb growth, and less commonly, meningoencephalitis (visna) and arthritis.

Purpose of the Study:

• To elucidate the pathogenesis of maedi-visna virus infection in sheep.
• To understand the role of macrophages in viral replication and inflammatory responses.
• To discuss factors influencing macrophage activation, viral transmission, and disease susceptibility.

Main Methods:

• The study reviews the replication cycle of maedi-visna virus, a lentivirus.
• It examines viral gene expression in circulating monocytes and tissue macrophages.
• The presence of viral antigens on macrophages in various tissues and their role in initiating inflammatory responses are discussed.

Main Results:

• Maedi-visna virus replicates via proviral DNA in monocytes and macrophages.
• Macrophages expressing viral antigens in lungs, udder, joints, and CNS act as foci for mononuclear cell inflammation.
• These inflammatory responses contribute to the clinical manifestations of the disease.

Conclusions:

• Macrophage activation is central to the inflammatory processes in maedi-visna virus infection.
• Understanding these mechanisms is crucial for managing viral transmission and disease susceptibility in sheep flocks.
• Further research into factors affecting macrophage activation can inform disease control strategies.