Introduction

Classification

Taxonomy

• Family: Poxviridae.
• Subfamily: Chordopoxvirinae.
• Genus:Leporipox.
• Species:myxoma virus.

Etymology

• Gk:muxa- slime, mucus.

Active Forms

Clinical Effects

Epidemiology

Habitat

• Virus remains infectious for several months in vectors such as fleas   Flea infestation  .
• Can survive for months or years in a dry, dusty environment.
• Wild rabbits act as a reservoir host for domestic rabbits.

Transmission

• Direct contact between rabbits.
• Aerosol, especially in large outbreaks.
• Biting arthropods such as mosquitos, fleas   Flea infestation  , fur mites   Cheyletiellosis  and biting flies can act as vectors. 
• Fomite spread from contaminated environment (spiny thistles, etc).

Pathological effects

• Myxoma virus can replicate in the presence of an active humoral immune response.
• This is carried out by:
  • Production of virus-encoded proteins that mimic host receptors or cytokines.
  • Retardation of anti-viral responses such as apoptosis (programed cell death).
• Inheritable resistance is reported but this may be due to emergence of viral strains of reduced virulence.
• South American rabbits (Slyvilagus brasiliensis)   Cottontail   are resistant to severe disease; localized skin tumors are observed.
• Infection with the related shope fibroma virus   Pox virus    Fibromatosis  or vaccination with an attenuated shope strain is protective against myxoma virus. Shope fibroma virus does not cause serious disease in European rabbits (Oryctolagus cuniculus).
• Causes myxomatosis   Myxomatosis  .
• The virus replicates subcutaneously at the point of infection to produce a gelatinous nodule in 2-3 days.
• Viremia develops, followed by localization in connective tissue cells.
• This stimulates cell proliferation, especially in the head, resulting in blepharoconjunctivitis     .
• Subcutaneous lesions may develop over the entire body.
• Death usually follows 11-18 days after the onset of clinical signs.

Other Host Effects

• Some rabbits show inheritable resistance.
• The virus is only mildly pathogenic in its native South American host (Sylvilagus brasiliensis)   Cottontail  .
• 5-10 year cycles, in which isolates of changed virulence appear, occur in wild rabbit populations.

Control

Control via animal

• Supportive therapy may be attempted, but case fatality is high.

Control via environment

• Reduce wild rabbit population in the immediate area.
• Prevent contact of domestic rabbits with wild rabbits.
• Control insect vectors such as mosquitoes, fleas, fur bites, biting flies.

Vaccination

• See Myxomatosis.

Print off the Owner factsheet Vaccinations - essential protection to give to your clients.

Diagnosis

Further Reading

Publications

Refereed papers

• Recent references from PubMed and VetMedResource.
• Spiesschaert B, McFadden G, Hermans K et al (2011) The current status and future directions of myxoma virus, a master in immune evasion. Vet Res 42 (1), 76 PubMed.
• Kerr P & McFadden G (2002) Immune responses to myxoma virus. Viral Immunol 15 (2), 229-246 PubMed.
• Marlier D, Mainil J, Linde A et al (2000) Infectious agents associated with rabbit pneumonia - isolation of amyxomatous myxoma virus strains. Vet J 159 (2), 171-178 PubMed.
• Gelfi J, Chantal J, Phong T T et al (1999) Development of an ELISA for detection of myxoma virus-specific rabbit antibodies - test evaluation for diagnostic applications on vaccinated and wild rabbit sera. J Vet Diag Invest 11 (3), 240-245 PubMed.
• Kerr P J & Best S M (1998) Myxoma virus in rabbits. Rev Sci Tech 17 (1), 256-268 PubMed.
• Flowerdew J R, Trout R C & Ross J (1992) Myxomatosis - population dynamics of rabbits (Oryctolagus cuniculus Linnaeus, 1758) and ecological effects in the United Kingdom. Rev Sci Tech 11 (4), 1109-1113 PubMed.
• Ross J, Tittensor A M, Fox A P et al (1989) Myxomatosis in farmland rabbit populations in England and Wales. Epidemiol Infect 103 (2), 333-357 PubMed.

Other sources of information

• van Pragg E (2010) Skin diseases of Rabbits. Website:www.medirabbit.com.
• Carter G R & Wise D J A (2005) Poxviridae. In:A Concise Review of Veterinary Virology. Eds: Carter G R, Wise D J & Flores E F. International Veterinary Information Service, Ithaca, New York. Website:www.ivis.org.