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Ovine diseases. Orf
1Moredun Research Institute, International Research Centre, Penicuik, Midlothian, Scotland, UK. haigd@mri.sari.ac.uk
Veterinary Research
|August 5, 1998
Summary
Orf virus causes skin lesions in sheep, goats, and humans. Despite a strong immune response, the virus can reinfect sheep due to specific virulence genes that overcome host defenses.
Area of Science:
- Virology
- Immunology
- Genetics
Background:
- Orf virus is a globally distributed DNA parapoxvirus causing skin lesions in livestock and humans.
- Orf virus exhibits a typical poxvirus gene distribution, with essential replication genes centrally located and virulence genes terminally positioned.
Purpose of the Study:
- To investigate the genetic basis of orf virus virulence and its interaction with host immunity.
- To identify specific orf virus genes contributing to immune evasion and recurrent infections.
Main Methods:
- Genome sequencing and genetic mapping of orf virus.
- Analysis of immune responses (T cells, interferons, antibodies) to orf virus infection.
- Identification and characterization of putative orf virus virulence genes.
Main Results:
- Orf virus infection elicits a robust antiviral immune response involving CD4+ and CD8+ T cells, interferons, and antibodies.
- Despite effective immunity, orf virus can repeatedly infect sheep, indicating mechanisms of immune evasion.
- Putative virulence genes identified include viral homologues of ovine VEGF and IL-10, an interferon resistance gene (E3L), and a GM-CSF inhibitory activity.
Conclusions:
- Orf virus possesses virulence factors that enable it to temporarily evade host immunity and promote viral replication.
- These virulence genes, including VEGF and IL-10 homologues, are crucial for orf virus persistence and reinfection in sheep.
- Understanding these mechanisms is key to developing strategies against orf virus infections.