HRS Article:   E. cuniculi

by Susan A. Brown, DVM

E. cuniculi is a one celled organism that is a parasite that can affect a number of different species of animals. It is a common finding in rabbits and the majority of the time itdoesn't cause any obvious clinical disease at all. It is spread through urine as the "adult" organisms reproduce in the kidneys. They may remain dormant throughout the rabbits life and never cause a problem after the initial infection or rarely they may migrate to nervous tissue and other organs. Most commonly signs of disease occur when there is damage to the nervous tissue (brain and spinal cord) and can include head tilts, paralysis, paresis and behavioral changes. However, it must be remembered that other disease can also cause these signs and it is basically impossible to say that E. cuniculi is causing the disease even with a positive titer. Up to 80% of NORMAL rabbits in some populations have POSITIVE E. cuniculi titers and they are not exhibiting disease, and may NEVER have any clinical disease. You also cannot use RISING titers as these have no significance in whether or not the E. cuniculi is causing the clinical signs being presented. The only way to diagnose that a disease is CAUSED by E. cuniculi is to look microscopically at samples of the nervous or other tissue and identify LARGE colonies of these organisms. Even at that, there is still much controversy in the veterinary field if this alone constitutes a diagnosis.

A couple of years back, there were some articles about using such drugs as oxibendazole in TISSUE CULTURES - NOT LIVE RABBITS that seemed to have a suppressive affect on the growth and reproduction of E. cuniculi. These drugs were NEVER tested in live rabbits and therefore we :

1. Do not know if they even work in the live rabbit and
2. Do not know the long term health effects to the rabbit by using these drugs. In theory, you would have to use these drugs for the life of the rabbit because they do not KILL the organism, but primarily keep it from reproducing. Therefore, in our practice, we do not recommend their use as there is no scientific basis for it and in fact we may ultimately cause harm. All of these drugs, after all, represent foreign substances introduced into an organism (the rabbit) whose functions are working in delicate balance.

There have been anecdotal reports that oxibendazole "cures" rabbits with E. cuniculi. NONE of these reports have been substantiated with definitive concrete data. I will tell you in practice that many rabbits that exhibit neurological disease improve with NO drugs, or with the short term use of corticosteroids, or antibiotics.....therefore, we cannot say that ANY drug really CURED the problem. What is most likely happening, is that the damage takes place when the parasite moves into the area (the brain form instance) and then it quiets down, the tissue heals as much as it can (with or without drugs...they won't help healing of brain tissue) and the rabbit recovers as much as he can which is sometimes complete return to normal

So, the bottom line is this:

1. E. cuniculi is a COMMON parasite in the normal rabbit population
2. A blood titer showing positive for E. cuniculi DOES NOT mean the rabbit is having clinical signs of the disease now, nor ever will. It simply means that the rabbit has been exposed to the disease at some point in its life.
3. A RISING blood titer to E. cuniculi does not mean anything significant...it cannot be correlated with clinical disease (this information is from the people who do research on this disease and who run the test)
4. Using clinically unproven drugs on rabbits for a disease they are likely to never develop is risky and we do not recommend it.

Dr. Susan Brown Chicago Chapter HRS Medical Director