by Paula Watkins

E. Cuniculi. If you have ever heard those words uttered by your vet in reference to your pet rabbit, no doubt you have left the office with more questions than answers. It is by all accounts, a very perplexing disease and I will attempt to shed some light on it here, as well as put some practical applications on it for us who live with rabbits in our home.

First of all, what is it?

E. cuniculi is the common abbreviation for Encephalitozoon cuniculi. It was originally classified as a protozoa but recently has been classified as a microsporidial parasite, which is a form of fungus. The life cycle of the parasite is three to five weeks during which time it sheds spores. It is usually transmitted in the urine of infected rabbits, either by ingestion of food contaminated by infected urine or inhaling the spores. These spores are able to survive outside the rabbit for a month, and the infected rabbit is able to transmit the disease for 90 days.

What happens once the rabbit becomes infected?

The parasite travels to the kidneys, liver, heart and brain where it takes up residence in the cells and replicates. During the three to five week life cycle, the spores can be shed in the urine. After that period the parasite remains in the body, but dormant. The initial infection is usually taken care of by the rabbit's immune system and a normal, healthy rabbit shows no symptoms. Statistics are anywhere between 50 and 80% of all rabbits have been exposed to e. cuniculi at some point. In those rabbits who develop symptoms, they become evident when the rabbit ages and their immune system starts to break down or they live in stressful conditions with poor diet and hygiene.

What are the symptoms of e. cuniculi infection?

Since the parasite travels through the neural system to the kidneys, then ultimately to the brain, heart and other vascular organs, symptoms can be seen in any of these areas. The rabbit may have signs of kidney disease, cataracts, neurological disease such as hind end weakness, head tilt or seizures or even heart failure. The difficulty of making a diagnosis of e. cunniculi comes in the fact that the only definitive diagnosis can be made after death when damage from the organism can be seen on necropsy.

What tests are there for e. cuniculi?

Unfortunately there is no current test available for showing evidence of the organism itself or its spores, though research is being done in this area. There is a test to show if the rabbit has had an immune response to the parasite - this is called an e. cuniculi titer. Some results of the titer can be very useful, if the titer is negative, it can be assumed that the rabbit has not been in contact with the e. cuniculi organism. If the titer is positive, there are many different ways it can be interpreted, part of the problem being the short time the rabbit is contagious and the results having no way of determining how long the titer has been elevated, therefore you do not know if the positive result means an active infection or a dormant one.

What treatments are there for e. cuniculi?

Fenbendazole (Panacur) has been shown to reduce spore propagation and spread and in the laboratory, it has also been shown to prevent the infection from occurring. This medication along with an NSAID such as meloxicam to reduce the inflammation caused by the infection is usually the two-pronged approach used. Neither of these medications is without side effects so should not be used unless symptoms are seen.

What now?

Okay, now I have this information, how does it affect my rabbit going forward with e. cuniculi? Is it fatal? Does he need to be on medication the rest of his life? He has a rabbit friend - do I need to get her tested or treated? Do I need to get all my rabbits tested, if they are negative do I need to test all their potential friends?

These are the questions I think all of us bunny parents really want to know and in all my research I cannot find good answers to them. All the experts seem to be in agreement that diagnosing and treating this disease is still a challenge, even after several decades of study so if the experts don't know, how are we to know?

My approach

As someone who has been in rabbit rescue for over fifteen years as a House Rabbit Society fosterer and educator and have had a hundred plus rabbits pass through my home, I prefer to take a practical approach, as does my rabbit savvy veterinarian. Statistics are clear that e. cuniculi is extremely prevalent in the rabbit population and that a very low number (I have seen as low as 7% but the average is 10%) ever come down with symptoms of active disease. Therefore, I prefer to treat it as a non-entity until I see symptoms of it in a rabbit. While we know that an infected rabbit can pass the organism in their urine for up to 90 days we have no documented evidence that a rabbit who has been treated with fenbendazole or a rabbit infected past the 90 day period has infected another rabbit. This information alone gives us "permission" to let all our rabbits treated equally regarding housing, finding friends, etc. I do not know of an experienced House Rabbit Society licensed educator who disagrees with this, and most of them have had many years of experience with e. cuniculi.

E. cuniculi in my own rabbits and fosters over the years

In my fifteen years I have unfortunately seen about every type of e.cuniculi symptom in rabbits coming through my home. A bonded pair of my own lost the female to renal failure at age six, e. cuniculi lesions were seen in her kidneys on necropsy. Her bonded brother lived to age 10 and died of "old age" - nothing specific, just faded away. So, if he was e. cuniculi positive from her it never affected him.

I have had foster rabbits pass away under anesthesia for spay/neuter surgery - e.cuniculi lesions were seen in their hearts.

My rabbit Harley developed head tilt (no evidence of ear infection was ever found) and renal failure later in life, and passed away from a seizure. No necropsy done but his bonded friend of many years passed away some years later from age related causes.

I had a four month old baby, Ella, who had head tilt due to what we thought was an ear infection. She did have an ear infection and was being treated for it when she passed away due to seizures. They also found e. cuniculi lesions in her brain.

Checkers had hind end weakness due to e. cuniculi, and tested positive for it. She was treated and with acupuncture lived four comfortable years, never progressing beyond the weakness in her rear legs.

In conclusion: Take it day by day, and just give your rabbit good care

There are more cases I could cite but overall I have come to the conclusion that e. cuniculi is a terrible disease, one you certainly do not want to get a diagnosis for your beloved rabbit! And, while the parasite will be with your rabbit for life, it does not mean an immediate death sentence. With good veterinary care your rabbit can have a good quality of life. E. cuniculi testing is not inexpensive and best a topic discussed with your vet. I would never advise breaking up a bonded pair over e. cuniculi, nor would I worry about testing for it when looking for a friend for my rabbit.

E. cuniculi has been around a long time and will be here a long time. I'm certain we will get medical breakthroughs on this disease as time goes by but in the meantime we need to take clues from our rabbits and just live life day to day.