Kevin Wright, DVM, DABVP (reptiles and amphibians)
Killing the E. cuniculi (EC) organisms does not make the lesions they have caused throughout a rabbit’s body go away. Sometimes killing the EC causes the body to create even more inflammation as it walls off or removes the decaying organisms in a rabbit. If this happens in the wrong areas of the nervous system, it may cause permanent head tilt, muscle weakness or other problems. If it happens in the heart, kidneys, liver or other organs, it may leave behind an organ that no longer works at top efficiency.
Unfortunately, no specific medications target microsporidians. Developing such a medication was not a priority for pharmaceutical companies until human patients with AIDS started to develop infections by unusual organisms, and then some cases of microsporidiosis were found in seemingly healthy humans.
Currently, humans with microsporidiosis are treated with albendazole when the infection involves the eyes, intestines or is spread throughout the body. Fumagillin eye drops have been used to treat infections of the cornea. Monthly thalidomide has helped with some infections, but its toxicity precludes widespread use and its mechanism of action isn’t well understood. To my knowledge, thalidomide has never been used on an EC-infected rabbit.
Albendazole, fenbendazole and oxfendazole are medications used to treat nematodes and other parasitic worms; they also happen to have some efficacy against EC. Albendazole has received a bad reputation in the pet rabbit community, which I find odd because it is the drug of choice in people. Albendazole does have adverse side effects, but there have been no peer-reviewed studies to prove that the alternatives, fenbendazole and oxfendazole, do not have similar side effects in EC-infected rabbits. The only peer-reviewed treatment study on EC rabbits used fenbendazole. Despite the flaws in this study, it has been the standard for deriving treatments for EC rabbits. For this reason, as well as its availability, affordability, shelf-life and acceptability to most clients over albendazole, I routinely prescribe fenbendazole for EC rabbits.
Due to the nature of the EC lesions, corticosteroids are sometimes given to try and reduce the inflammation in the brain. The risk is that corticosteroids may suppress the immune system to the point that EC or other infectious organisms may create additional problems; for that reason, some veterinarians choose to go with nonsteroidal anti-inflammatory drugs (NSAIDS), such as meloxicam. Corticosteroids such as prednisone or dexamethasone seem to be more effective than meloxicam, but it may be that the dose of meloxicam advised for rabbits does not provide adequate blood levels. There has been no study that gives a definitive answer for how much meloxicam a rabbit should be given in order to control inflammation, nor what dose of corticosteroid is best. Never give corticosteroids with meloxicam as this can cause stomach ulcers!
Doxycycline, an antibiotic with some anti-inflammatory properties, is sometimes given along with corticosteroids or meloxicam. Red palm oil and other balanced omega fatty acid mixtures may be helpful in reducing inflammation. I’ve used Booster, a proprietary product from Harrison’s Pet Products, which has red palm oil and a specific substance that has antibiotic properties, with EC-infected rabbits but it is difficult to evaluate its overall impact given the other medications that have been given in the course of treatment.
Ponazuril, a medication effective against Coccidia, and ivermectin, a medication effective against nematodes and other invertebrate parasites, are given by some veterinarians. Lufenuron, a flea treatment that inhibits chitin production, has been tried on the assumption that one part of the microsporidian life cycle, the endospore, has chitin. A combination treatment of pyrimethamine, sulfadiazine, folic acid, and meloxicam has been tried extrapolating from some work done on horses with certain parasites. Enrofloxacin and chloramphenicol, both antibiotics, are sometimes given. Many other medications have been tried. However, it is uncertain if any of these treatments have anti-microsporidian properties, because no peer-reviewed controlled studies or peer-reviewed retrospective studies have been done that assess the validity of the claims that are made. Furthermore, all of these medications are extra-label use in rabbits.
Seizuring rabbits need emergency care. If they do not respond to medications, such as intravenous diazepam or barbiturates, the prognosis is poor and euthanasia should be considered.
Nursing care includes assist-feeding with a liquid diet, providing subcutaneous fluids if a rabbit cannot stay well-hydrated and applying eye lubrications. Meclizine or other anti-nausea/anti-vertigo medications may help improve the attitude and appetite of a rabbit that is rolling. Cleaning the rump area to remove night feces and other debris helps prevent scalding in a rabbit unable to do these tasks for himself. A soft, cushioned environment is needed for rabbits that are rolling, something like a large plastic tub lined with towels or soft cushions. A rabbit with a head tilt will benefit from massage to help relieve the stress of the abnormal muscle posture.
It may take weeks for a rabbit to show significant improvement. Many have a permanent head tilt but otherwise seem to have a normal quality of life.
Rabbits with cataracts may undergo surgery to remove the problem lens. This surgery is costly and not every ophthalmologist is willing to work on rabbits. However, if the infected lens is left in place it might rupture and cause further inflammation in the eye even with prophylactic drug therapy that includes fenbendazole.
There are many treatment regimens out there, as well as success stories and horror stories. Unfortunately, if you haven’t proven that EC is the cause of a rabbit’s illness, you can’t say that the treatments given to that rabbit will work on any other rabbit. Other ailments, such as injuries, ear infections and poisonings, among others, can mimic the signs of EC.
Preventing E. Cuniculi Infection
There is no vaccine to prevent EC. At some point or another, almost every rabbit is going to be exposed to the organism.
An infected rabbit, guinea pig, mouse or other mammal, can re-infect the environment throughout his life. As mentioned earlier, EC spores stay alive for months under the right conditions. Fortunately, chlorine bleach and many other readily available disinfectants kill the spores.
To combat EC spores, first, you must thoroughly clean the rabbit’s environment to remove obvious urine, feces and other organic dirt, such as pellets and hay. Next, wash the cage, food bowls and other furnishings in hot, soapy water to remove the invisible dirt. Rinse in hot water and follow up with disinfection by applying a diluted solution of bleach (1:32) to the items and let them sit for 15 to 30 minutes before rinsing in fresh hot water. Any towels or cloth items need to be washed in hot, soapy water and also bleached. If you do not want to fade your cloth items, use a commercial disinfectant such as Roccal. Vinegar is often touted as a safe disinfectant, but it may not kill EC spores.
EC spores can be anywhere your rabbit was, such as the couch, carpet or bed, and the spores can float around in the air and reach other places too. If you have an EC-positive rabbit, your whole household should be considered contaminated.
What this means is that any rabbit coming into your household is being exposed to the EC spores, and any other rabbit owners who visit may pick up spores that they can bring back to their own pets. You don’t need to be considered a pariah, though, because almost every pet rabbit has been exposed to EC at some point in his life and, as previously mentioned, either successfully fought the infection so he is not ill or has already contracted the infection and shown signs of illness.
Controversy exists about how to manage EC-positive rabbits. I recommend that any EC-positive rabbit, whether or not he shows signs of illness, is treated monthly with a 3- to 5-day course of fenbendazole. Other rabbits in the household may get monthly doses. Any new rabbits coming into the household are put on the same monthly dose. Anytime a rabbit undergoes stress, such as travel, boarding or other unusual activity, I put him on prophylactic fenbendazole.
Let me re-emphasize that almost all pet rabbits have been exposed to EC at some point in their lives. Even if you practice good hygiene, there’s a chance your rabbit may still contract EC.
E. cuniculi is a disease that you and your veterinarian need to think about if your rabbit is ill, and screening for EC should be part of the wellness program for any pet rabbit. If your rabbit develops signs, early treatment is more likely to help than care that is started several days after the first signs of illness. A coordinated effort to provide major funding for EC research of pet rabbits is needed if we are to make any advances in its prevention and treatment.
This article was originally published in the 2012 issue of Rabbits USA magazine.
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