Myxomatosis, sometimes shortened as myxo, is a disease caused by the myxoma virus, a strain of Leporipoxvirus, that affects rabbits. It is a usually fatal disease in domestic and wild old-world rabbits and more likely when mosquitos are numerous such as the summer and fall. The virus is spread primarily through insect bites (mosquitoes, flies, fur mites, fleas, ticks), but it can also be transmitted by mechanical factors such as nonbiting insects, thorns, bedding, and food.
Myxomatosis was first reported by an Italian microbiologist in 1896 when a laboratory rabbit colony he had imported into Uruguay for public health research suddenly died of an extremely infectious disease. The virus was identified in the 1930s and had been intentionally introduced in Australia and France in biological warfare against the rabbit population in the 1950s. It spread from France to the UK in 1953 where it decimated the European wild rabbit population. Resistance has since developed. Several strains of myxoma viruses exist.
Myxomatosis can be found in Europe, South America, North America, and Australia. In the United States, the disease is seen primarily in California as an extremely virulent strain with mortality rates exceeding 99%.
The Myxoma virus causes a trivial infection in its natural host, either Sylvilagus brasiliensis (Tapeti, forest rabbit, found in Mexico or Argentina) or Sylvilagus bachmani (brush rabbit), which is native to California. Myxomatosis can occur in hares but infection is rare and usually mild.
For the California strain of myxo in domestic rabbits, incubation period is usually 1 to 3 days. It can attack domestic rabbits in peracute (extremely active and violent), acute, and chronic forms.
The disease starts with a skin lesion which typically develops 4 to 5 days after inoculation and enlarges to about 3 cm in diameter 9 to 10 days after infection. The eyelids become thickened and then completely closed by the 9th day with a semipurulent ocular discharge. Secondary lesions develop throughout the body, typically on the nares, lips, eyelids, and base of the ears and on the external genitalia and anus.
Rabbits vaccinated against myxomatosis can also be affected and develop an atypical form of the disease called lumpy bunny syndrome. The severity of the disease is variable and can range from a single lump to multiple skin lesions.
Treatment and prevention
Unfortunately, most treatment for myxomatsosis is non-effective, and supportive care is generally unsuccessful. Myxomatosis is usually fatal for domestic rabbits due to exhaustion from lack of nourishment or secondary bacterial infection. However, high ambient temperature of over 85°F can increase recovery rate.
Rabbits with lumpy bunny syndrome have a less bleak prognosis, and many of them can recover with appropriate supportive care.
To prevent myxo, your best options are to do the following:
- Control its vectors - add screening to keep out insects; use flea control; keep your rabbits indoors.
- Disinfect - 10% bleach, 10% NaOH, 1% to 1.4% formalin
- Quarantine new rabbits and do not house wild rabbits with domestic pet rabbits.
- Vaccinate your rabbits if it is available in your country. It can provide temporary protection. Unfortunately the vaccination is not available in Australia or the United States.
- House Rabbit Society. (2017). Myxomatosis in the US
- Bunny Bunch S.P.C.R. (2010). Myxomatosis Alert in San Gabriel, California
- Poublon, J. (2014). Myxomatosis: Vaccination
- van Praag, E. (2010). Myxomatosis in rabbits
- McLeod, L. (2017). Myxomatosis in Pet Rabbits
- Foster and Smith. Myxomatosis in Rabbits: Transmission, Signs, Diagnosis, Treatment, Prevention
- Kerr, PJ, & Best, SM. (1998). Myxoma virus in rabbits [PDF]
- Mayer, J. Viral Diseases of Rabbits
- Rabbit Welfare Association & Fund. (2006). Deadly, But Preventable: What rabbit owners need to know about myxomatosis & VHD. [PDF]
- Stern, H. (2014). Myxomatosis Outbreak – Bring your Bunnies Indoors!
- Hood, GM et al. (2000). Biological control using sterilizing viruses: host suppression and competition between viruses in non-spatial models
The following pages are from rabbit breeding websites. Please note that we do not condone breeding for the common pet owner and provide these links for information only.
- Three Little Ladies Rabbitry. Myxomatosis and Your Rabbits Health
The following groups are resources to help keep track of outbreaks in countries that have regular occurrences of myxo.
- Facebook. Myxomatosis map for the UK
- Watkins & Tasker Veterinary Group. (n.d.) Myxomatosis in rabbits. Retrieved 2 June 2016 from https://www.vetstream.com/watkinsandtasker/html/Factsheets/Otherpets/24_286496.asp
- Varga, M. (2013). Textbook of rabbit medicine. (2nd ed.).
- Oglesbee, B. (2011). Blackwell's five-minute veterinary consult: Small mammal. (2nd ed.).