Myxomatosis

By Jean Silva

Myxomatosis, like violent crime, is not something we think about until it happens to us.  Then, in the midst of the devastation we can think of little else. Myxomatosis is a fatal disease of rabbits that is present in Santa Barbara County and other parts of California.  

A rabbit infected with the Myxoma virus may experience high temperatures, discharge from the eyes and nose, swelling at the base of the ears, eyelids, muzzle, and genitals.  Red rimmed eyes, when they occur, are easy to see.  Rabbits will be less active and their appetite may decrease. In some rabbits, death occurs before signs of the disease are readily noticed. In other rabbits, the appearance of the disease becomes marked.  Eye lids will droop and appear half closed. Swelling will cause the ears to droop to the side. The rabbit will be slow to rouse as if in a stupor. 

Sadly, there are no treatments available for myxomatosis. Antibiotics are ineffective.  There are no viral suppression drugs for myxomatosis.  The survival rate approaches zero. Euthanasia is the kindest course of action.

While the myxoma virus is deadly for rabbits, it does not affect other mammals.  People, dogs, cats, birds, guinea pigs, ferrets, and other pets are not at risk.

The myxoma virus lives in the wild rabbit population (Sylvilagus bachmani). Unlike pet rabbits, the brush rabbit has developed resistance to the myxoma virus. Infected brush rabbits are the reservoir in which the virus survives.  The virus relies on mechanical transmission to spread from rabbit to rabbit. Mosquitoes are the most effective vector.  A mosquito inserts his proboscis into an infected rabbit and collect virus on the proboscis. That mosquito will insert virus into his next victims.  It is estimated that a mosquito can transmit virus to up to 5 subsequent victims.  Fleas, ticks, flies and other biting insects can also transmit the virus.

We do not know which mosquitos are the most likely to transmit the virus in Santa Barbara County.  There are fifteen species and four genera (Aedes, Anopheles, Culex and Culista) of mosquitos in our County.  All of them can transmit the virus. Each species of mosquito has a its own preferences for feeding and breeding.  Some mosquitos can travel over a mile and as much as five miles from their birth place. The Mosquito and Vector Management District of Santa Barbara County http://www.mvmdistrict.com is the best source of information about mosquitoes near you. 

The district has trapped every species of mosquitoes in Santa Barbara County at Lake Los Caneros. But, mosquitos can also breed in your back yard. Anything that will hold water more than a few days can breed mosquitos: ponds, pools, gutters, drains, bird baths, boats, wheel barrows and leaky watering equipment. Wet lands and tree holes can also be breeding areas. If you have a pond or other standing water the district provides mosquito fish free of charge. 

Rabbit owners on the south coast should assume that their pet rabbits are at risk of myxomatosis.  But how to measure the risk?  If you are near a population of wild rabbits and you are near a source of still water, your risk is higher.  Even then a mosquito or other bug must bite a sick rabbit and then bite your bunny. Until that happens your bunny won’t get myxomatosis.   Even if you think the risk is small, the outcome is so dire that you should consider prevention.

The safest place for your rabbit to live is in your house with screen doors and screened windows.  If your rabbit lives in an outdoor hutch, then staple mosquito screen over wire sides and doors. If your hutch has a wire floor and an under tray, consider how to screen the gaps between the tray and the sides of the hutch. A a solid floor of plywood, linoleum, or tile also works.  Keeping your rabbit in a garage or closed out building at night is another option.  Regularly check your screens and repair any tears.

If your bunny plays or lives outdoors, make your yard mosquito free.  Look for and drain all collections of standing water. The Mosquito and Vector Management District has a pamphlet on its web site, showing where water can collect around your home. 

Limit the times of day your bunny is allowed to play in the yard.  Put your bunny out in mid morning and bring it inside in the late afternoon.  Most Culex and Anopheles mosquitoes feed at night.  Aedes feed during the day and in the early evening.  .

There are commercial mosquito traps available. These traps use CO2 and or light to attract mosquitoes. Prices for these traps range from $100 to $899.  Placement of the trap is critical to its effectiveness.  To be effective, the trap should be placed upwind between a mosquito breeding area and your rabbits. If placed too close to your rabbits, mosquitos attracted by the trap, may target your rabbits visually or thermally.  According to Consumer Reports tests from 2003, the most effective CO2 traps left 25% of the mosquitoes after 20 hours in a closed room. So traps are not a compete solution.

Consider using flea control and mosquito repellants. If you have a dog or a cat with access to the outdoors regular flea treatments are advised.  Vectra 3D, for dogs provides flea control and repels 80% of Aedes and Culex mosquitoes. Those are two of the four genera of mosquitoes in our county.  Use of Vectra 3D for rabbits is off label. I use it under the direction of my veterinarian. If you wish to use it, check with your vet. 

If a rabbit, especially one in a multiple rabbit household, contracts myxomatosis you must isolate it immediately. If you are not treating your rabbits for fleas, you should treat all your rabbits as quickly as you can.  If you cannot isolate the sick rabbit at home, take it to your vet. You will need to euthanize a rabbit with myxomatosis, so you must decide when to do so. Consider the threat to remaining rabbits, both in your household and in the neighborhood.  Consider the degree of suffering your rabbit is experiencing. Decide how best to say good bye to your friend.

I know how difficult and painful loss can be. So take time to be your rabbit’s friend while he is healthy. Give him a good quality of life and take as many precautions against myxomatosis as you can manage.