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Myxomatosis

Clapis

Introduction

  • Myxomatosis was first described in laboratory rabbits in Uruguay in 1896. The myxoma virus was identified in the 1930s and subsequently used in biological warfare against the rabbit population of Australia and France in the 1950s. It spread from France to the UK in 1953 where it decimated the European wild rabbit population. All pet rabbits, both indoor and outdoor rabbits, are at risk. Rabbits living outside (especially if wild rabbits enter the garden) are at greater risk.
  • Cause: myxoma virus (a double-stranded DNA poxvirus) Myxoma virus is spread by biting flies or fleas and by mechanical vectors such as non-biting insects, bedding and food. Direct spread via respiratory secretions between rabbits is possible, but an uncommon route of spread.
  • Signs: severe edema of lips, eyelids and genitals, pyrexia, depression, chronic localized skin nodules, up to 100% mortality in acute systemic form, much lower in the more chronic nodular form which only affects skin.
  • Diagnosis: clinical signs, viral testing may be performed.
  • Treatment: supportive and palliative only.
  • Prognosis: very poor in the acute systemic form. Good to excellent in the more chronic skin form.

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

Presenting signs

  • In the acute form, the initial signs are lethargy and conjunctival erythema with watery or milky ocular discharge progressing rapidly to severe edema of the lips, eyelids and genitals.
  • The chronic nodular form manifests by edematous swellings called 'pseudotumors', or myxomas which develop within 10-15 days on the ears, nose and paws. These typically regress, leaving skin lesions.

Acute presentation

  • The acute presentation is a highly contagious, high mortality form (up to 100% in unvaccinated rabbits).
  • The incubation period has been reported to be 8-21 days.

Geographic incidence

  • Myxomatosis is widespread throughout the UK and has a higher seasonal prevalence in late summer, autumn and early winter. It is perhaps more commonly seen in the warmer parts of the UK and has a longer season there.
  • In one study, cases were reported in all months but February and were distributed across the country.

Morbidity

  • Both pet and wild rabbits are susceptible with no breed specificity.
  • The European Brown Hare can sometimes be affected.

Mortality

  • There can be up to 100% mortality in the acute form.
  • The chronic form has a more than 50% survival rate so may be worth treating supportively. Recovery can take weeks to months.
  • A milder form of the chronic nodular form may be seen in vaccinated rabbits, from which they usually recover unremarkably with supportive nursing treatment, eg nutritional support if the lesion is affecting appetite, if on the lips. A scabbing lesion on the nose or face is a common presentation, sloughing 10-14 days later, leaving variably sized wounds which may need further management.

Age predisposition

  • In wild rabbits, juveniles are more susceptible, and antibody levels rise rapidly in their first year of life as they develop immunity against it. There is maternally derived immunity for 4-5 weeks post weaning, eg up to approximately 10 weeks of age. There is some degree of paternally derived immunity from bucks previously infected within 7 months of conception.
  • In domestic rabbits maternally derived protection due to natural infection of the dam is unlikely, and would rely on previous vaccination of the dam. Naïve animals of any age are equally susceptible to disease.

Sex predisposition

  • In one study it was reported that female entire pet rabbits were almost twice as likely to be affected by myxomatosis in the study population.
  • Further studies are required to understand those features of entire female rabbits and their care that place them at heightened risk for myxomatosis. It has also got to be considered that neutering was less common than for cats and dogs. In another study it was reported that only 45.8% of rabbits were neutered, and that neutering was also less common in female rabbits.
  • In wild populations males show a greater tendency to roam, being most at risk.

Breed predisposition

  • None known, although an atypical form is known to affect angora rabbits following the stress of being plucked for wool, akin to the chronic nodular form above. Mortality is low.

Public health considerations

  • Few.
  • Myxomatosis is not itself a health issue for non-lapine species.
  • Secondary Pasteurella infection may render wild shot rabbits with myxomatosis unsuitable for human or animal consumption, but such animals are obvious and would be rejected for eating.

Cost considerations

  • Expensive - affected rabbits usually require very intensive nursing and supportive therapy.
  • Mortality is high despite treatment.

Special risks

  • The involvement of the lungs, with pulmonary edema common in the later stages, makes such animals a high anesthetic risk (ASA Grade 2-5 depending on lung involvement). The biggest risk is infection of other rabbits within the practice.

Pathogenesis

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Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Farrell S, Noble P J-M, Pinchbeck G L et al (2020) Seasonality and risk factors for myxomatosis in pet rabbits in Great Britain. Prevent Vet Med 176, 104924 PubMed.
  • Sánchez-Vizcaíno F, Noble P-J M, Jones P H et al (2017) Demographics of dogs, cats, and rabbits attending veterinary practices in Great Britain as recorded in their electronic health records. BMC Vet Res 13, 218 PubMed.
  • Meredith A (2012) A vaccine against myxomatosis and RHD: a step forward for rabbit health. Vet Rec 170 (12), 307-308 PubMed.
  • Spibey N, McCabe V J, Greenwood N M et al (2012) Novel bivalent vectored vaccine for control of myxomatosis and rabbit haemorrhagic disease. Vet Rec 170 (12), 309 PubMed.
  • Sant R & Rowland M (2009) Skin disease in rabbits. In Pract 31 (5), 233-238 VetMedResource.
  • Scarff D (2008) Skin diseases of pet rabbits. UK Vet: Companion Animal 13 (2), 66-75 VetMedResource.
  • Marchandeau S, Bertagnoli S, Peralta B et al (2004) Possible interaction between myxomatosis and calicivirosis related rabbit haemorrhagic disease affecting the European rabbit. Vet Rec 155 (19), 589-592 PubMed.
  • Farsang A, Makranszki L, Dobos-Kovács M et al (2003) Occurrence of atypical myxomatosis in Central Europe: clinical and virological examinations. Acta Vet Hung 51 (4), 493-501 PubMed.
  • Calvete C, Estrada R, Villafuerte R et al (2002) Epidemiology of viral haemorrhagic disease and myxomatosis in a free-living population of wild rabbits. Vet Rec 150 (25), 776-82 PubMed.
  • Robinson A J, Müller W J, Braid A L et al (1999) The effects of buprenorphine on the course of disease in laboratory rabbits infected with myxoma virus. Laboratory Animals 33 (3), 252-257 PubMed.
  • Hillyer E V (1994) Pet rabbits. Vet Clin North Am Small Anim Pract 24 (1), 25-65 PubMed.
  • Marshall I D (1959) The influence of ambient temperature on the course of myxomatosis in rabbits. J Hyg Lond 57 (4), 484–497 PubMed.
  • Hyde R R & Gardner R E (1932) Infectious myxoma of rabbits. Am J Epidemiol 17 (2), 446-465 OxfordAcademic.

Other sources of information

  • Delaney M A, Treuting P M & Rothenburger J L (2018) Lagomorpha. In: Pathology of Wildlife and Zoo Animals. Eds: Terio K A, McAloose D & St Leger J. Academic Press, UK. pp 481-497.
  • Meredith A (2014) Dermatoses. In: BSAVA Manual of Rabbit Medicine. Eds: Meredith A & Lord B. BSAVA, UK. pp 255-263.
  • Knott T (2014) Ophthalmology. In: BSAVA Manual of Rabbit Medicine. Eds: Meredith A & Lord B. BSAVA, UK. pp 232-254.
  • Varga M (2015) Textbook of Rabbit Medicine. 2nd edn. Butterworth Heinemann, UK.
  • Harcourt-Brown F (2002) Textbook of Rabbit Medicine. 1st edn. Butterworth Heinemann, UK.
  • Robinson & Kerr (2001) Infectious Diseases. In: Infectious Diseases of Wild Mammals. Eds: Williams E S & Barker I K. Iowa State University Press, USA. pp 179-201.
  • Okerman (1998) Disease of Domestic Rabbits. 2nd edn. Blackwell Science, USA.
  • Harkness & Wagner (1995) The Biology and Medicine of Rabbits and Rodents. 4th edn. Wiley-Blackwell, USA.
  • Fenner & Radcliffe (1965) Myxomatosis. Cambridge University Press, UK.
  • Rabbit Welfare Association & Fund (RWAF) Myxomatosis. Website: www.rabbitwelfare.co.uk

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