CORVALLIS - For the second year, an outbreak has been confirmed in Oregon of a rabbit disease called myxomatosis, and veterinary experts at Oregon State University say that rabbit owners should understand the continued threat from this disease and consider precautions to protect their animals.
Last summer, the first serious outbreak of the disease in more than a decade was identified in Linn and Benton counties in Oregon, prompting the closure of rabbit shows at the county fairs in those two areas. Myxomatosis is a disease with an extremely high mortality rate that shows up somewhat unpredictably in the European rabbits most commonly reared in Oregon.
In the past two weeks, about 14 of the 21 rabbits owned by a resident of Rogue River in southern Oregon died, and a necropsy on one of the animals by pathologists in the OSU College of Veterinary Medicine has established the diagnosis of myxomatosis.
"Mid- to late-July is about when we would expect to see problems from a continuing epidemic of myxomatosis, but at this point we have no reason to believe the problems will be as bad as last year," said Dr. Christiane Loehr, an OSU veterinary pathologist. "It's at least possible that last year was the peak of this epidemic and the problem will slowly improve. It depends partly on how bad of a mosquito season we have, which plays a role in transmission of the disease."
There are no official recommendations at this time to avoid rabbit shows, Loehr said.
"Mostly, we just want to remind people who own rabbits that this disease is still with us, that they should learn about the problems it can pose and consider taking precautions to protect their animals," Loehr said.
Myxomatosis is highly contagious, is transmitted naturally by mosquitoes or other insects, and can be spread from rabbit to rabbit by human handlers. It has no cure. In Oregon there is no diagnostic test for live animals and no readily available vaccine. The last time a major outbreak occurred in the 1980s it caused a significant number of rabbit deaths in the Willamette Valley and southern Oregon. The disease can have a mortality rate higher than 90 percent in European rabbits. There are some basic precautions that rabbit owners can take to protect their animals, experts say.
The most important is mosquito netting, which may help protect against mosquito and other insect transmission. However, animal handlers should be careful about use of such netting in very hot weather, since it may impair air flow in rabbit hutches.
Beyond that, the best prevention is avoiding groups of other rabbits that may be infected, such as at rabbit shows or county fairs.
Myxomatosis is caused by a poxvirus that has a natural reservoir, perhaps among brush rabbits. It is far less deadly to wild rabbits, although they, too, can be affected. It's not clear what triggers the periodic outbreaks among domesticated rabbits, but possible factors may include immunity levels in wild populations, heat stress, other weather conditions, and wild rabbit and mosquito populations.
Symptoms of the disease can include high fever, loss of appetite, swelling of mucus membranes or sluggishness. Mortality is linked to a suppression of the animals' immune system, making them vulnerable to a host of other health problems. Skin nodules called "myxomas" may appear in some cases. But at times an animal has appeared fairly healthy, and then died the next day.
There is no treatment other than supportive care for secondary infections, veterinary doctors say, and no vaccine is readily available. All domesticated rabbits in the U.S. are highly susceptible to the virus, but humans are not. If a rabbit is exposed to an infected rabbit, it should be quarantined for 14 days and assumed to be infected during that period. To help monitor the spread of the disease, anyone who owns a rabbit that dies from an unknown cause is encouraged to contact their local veterinarian or arrange for a necropsy by the Veterinary Diagnostic Laboratory at OSU, at 541-737-3261. There will be a fee for the necropsy.
More detailed information on myxomatosis is available on the website of the OSU College of Veterinary Medicine, at http://www.vet.orst.edu.
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Dr. Christiane Loehr, 541-737-9673