Malignant Catarrhal Fever Virus

VIRUSES HERPESVIRUSES

Hosts

• Reservoir species: wildebeest, sheep, each transferring different forms of the virus
  • Innocuous to reservoir hosts
• Dead end hosts: cows, kudu, some deer

Pathogenesis

Sever Oculo-nasal Discharge of MCF (Courtesy of Alun Williams (RVC))

• Clinical signs in cattle:
  

  Fissures on tongue (no vesicles) in MCF (Courtesy of Alun Williams (RVC))
  • Necrotising lesions in upper respiratory tract and eye: conjunctivitis and corneal oedema / opacity (keratitis or "blue eye" - characteristic feature)
  • Fever and diarrhoea with severe oculo-nasal discharge
  • Not eating, dull with ulcers on muzzle may spread to rest of face with brown exudate
  • Ulcers also on tongue, dental pad, and cheeks that regularly become secondarily infected
  • Lymphocyte proliferation progresses in lymphoid tissue and blood until death

• Lymph nodes completely replaced by lymphoblasts - similar to lymphosarcoma; synonym lymphoma. (resembles lymphotropic herpes virus such as Epstein Barr)
• Also vasculitis with medial necrosis of blood vessels throughout body with infiltration of walls of vessels by lymphocytes.
• Ulcers are due to hypoxia of epithelium resulting from vascular lesions
• Sporadically induce a fatal over-active T cell division, where virus encodes anti-apoptotic protein in dead-end host
• Latent infection that is invariably fatal
• Virus excretion increased during periparturient period

Epidemiology

• Not all that common in UK
• Affects whole body but especially evident clinically in face and mouth
• Sporadic and often seen in animals mixing with sheep (carriers)
• In parts of Africa see long outbreaks (diff serotypes) carried by Wildebeest
• In deer produces very serious outbreaks, probably primarily sheep virus
• Often youngish animal 6 months to 1 year

Control

• Wildebeest should not be stocked in zoos where possible
• Sheep and deer should be housed separately