Myxomatosis is a severe and usually fatal viral disease of European rabbits (Oryctolagus cuniculus) caused by the myxoma virus, a poxvirus. The disease is endemic in the United Kingdom, continental Europe, and Australia, where it was deliberately introduced in the 1950s as a biological control agent for wild rabbit populations. Myxomatosis is rare in the United States (limited to the West Coast) but remains a devastating threat to pet rabbits in endemic areas. There is no specific antiviral treatment, and the mortality rate in unvaccinated European rabbits is approximately 95 to 99%. Vaccination is the primary preventive strategy in endemic regions.
Overview
The myxoma virus is transmitted primarily by biting insects:
- Rabbit fleas (Spilopsyllus cuniculi) — The primary vector in the UK
- Mosquitoes — The primary vector in Australia and parts of continental Europe
- Direct contact — With infected rabbits or contaminated objects (fomites)
The virus is highly species-specific, primarily affecting European rabbits (Oryctolagus cuniculus), which includes all domestic pet rabbits. Wild cottontail rabbits (Sylvilagus species) in the Americas are the natural reservoir and typically show only mild disease.
Incubation period is typically 5 to 14 days after exposure.
Symptoms
Myxomatosis presents in two forms:
Classic (nodular) form:
- Swelling and edema of the eyelids, face, ears, and genital area (the hallmark “lion head” appearance)
- Conjunctivitis with purulent discharge progressing to sealed-shut eyes
- Swollen, thickened ears (hot, edematous)
- Subcutaneous nodules (myxomas) on the body
- Nasal discharge
- Fever, lethargy, anorexia
- Progressive decline and death within 10 to 14 days in unvaccinated rabbits
Atypical (amyxomatous / respiratory) form:
- Pneumonia and upper respiratory signs
- Less dramatic swelling
- Skin nodules may be absent or mild
- Can be more difficult to diagnose clinically
- Still carries a high mortality rate
Secondary bacterial infections (pneumonia, skin infections) commonly complicate the disease.
Diagnosis
- Clinical presentation — The classic facial swelling and conjunctivitis in a rabbit in an endemic area is highly suggestive.
- PCR testing — Confirms myxoma virus from skin lesions, conjunctival swabs, or blood.
- Histopathology — Skin biopsies showing characteristic myxoma cells with eosinophilic intracytoplasmic inclusions.
- Differential diagnosis — Must be differentiated from pasteurellosis, abscesses, allergic reactions, and other causes of facial swelling.
Treatment
There is no specific antiviral treatment for myxomatosis. Treatment is purely supportive, and the decision to treat vs. euthanize is guided by the severity of disease and the rabbit’s quality of life:
Supportive Care (For Rabbits With Mild to Moderate Disease)
| Treatment | Purpose |
|---|---|
| Subcutaneous fluids | Maintain hydration |
| Syringe feeding (Critical Care) | Nutritional support for rabbits unable to eat due to facial swelling or lethargy |
| Meloxicam | Pain and inflammation management |
| Antibiotics (enrofloxacin, trimethoprim-sulfa) | Treat secondary bacterial infections (pneumonia, skin infections) |
| Ophthalmic care | Clean eyes, apply lubricant and antibiotic ointment |
| Warmth and stress reduction | Support immune function |
Euthanasia Considerations
For many rabbits with classic myxomatosis, particularly those that are unvaccinated and showing severe disease (complete facial swelling, inability to eat or see, respiratory distress), humane euthanasia may be the most compassionate option given the extremely high mortality rate and significant suffering involved.
Prevention
Vaccination (Available in the UK and Europe; NOT available in the US or Australia)
- Nobivac Myxo-RHD PLUS — A combined vaccine protecting against myxomatosis and both strains of rabbit hemorrhagic disease (RHD1 and RHD2). Given annually from 5 weeks of age. Provides protection starting approximately 3 weeks after vaccination.
- Vaccination does not provide 100% protection but dramatically reduces disease severity. Vaccinated rabbits that contract myxomatosis typically develop a milder form with a significantly higher survival rate.
Other Preventive Measures
- Insect control — Use fly screens on outdoor enclosures, eliminate standing water near hutches, and apply rabbit-safe insect repellents (consult your veterinarian).
- Flea prevention — Regular flea treatment (selamectin/Revolution is commonly used in rabbits) to prevent flea-mediated transmission.
- Avoid contact with wild rabbits — Prevent access to areas frequented by wild rabbits.
- Quarantine — Isolate new rabbits and any rabbit showing illness.
Prognosis
- Unvaccinated rabbits — Mortality rate approximately 95 to 99%. Death typically occurs within 10 to 14 days.
- Vaccinated rabbits that become infected — Much milder disease; many survive with supportive care.
- Rabbits that survive — May develop some immunity but can remain carriers and may have residual scarring. Recovery can take weeks.
Frequently Asked Questions
Why is there no myxomatosis vaccine available in the United States? Myxomatosis is very rare in the US (limited to the West Coast), and the disease is not considered a significant threat to the domestic rabbit population nationally. Therefore, vaccine manufacturers have not sought US market approval. If you live in an area where myxomatosis has been reported, discuss risk-mitigation strategies with your veterinarian.
Can indoor rabbits get myxomatosis? Yes, though the risk is lower. Mosquitoes and fleas can enter homes, and the virus can be carried on clothing or objects. Indoor rabbits in endemic areas should still be vaccinated.
Is myxomatosis contagious to humans or other pets? No. Myxoma virus is highly species-specific to rabbits and does not infect humans, dogs, cats, or other animals.
Should I vaccinate my rabbit if it lives indoors? In endemic areas (UK, Europe), yes. Indoor rabbits are at lower but not zero risk. Annual vaccination is recommended for all pet rabbits in these regions.
Can a recovered rabbit infect other rabbits? Potentially, yes. Recovered rabbits may shed virus for a period after clinical recovery. Isolate recovered rabbits from unvaccinated rabbits and consult your veterinarian about the appropriate isolation period.