I wanted to add some additional information I have found about this disease, at this point I have not encountered it nor have I had any rabbits come down with wry neck (knock on wood). Wendy Feaga DVM, has published articles about wry neck and a possible connection to E. cuniculi (JAVMA Vol 210 No. 4 2/15/97 Letters to Editor). She had 20 rabbit brains tested, 10 were control rabbits and 10 were rabbits with wry neck. Of the 10 with wry neck 9 had encephalitis, in 7 of 9 lesions consistent with encephalitoozoon were found. Based on Dr Feaga's findings a number of wry neck cases may actually be the result of brain inflammation due to the immune response against E. cuniculi. She has reported success with treating wry neck with prednisolone at 11 mg/kg of body weight. She reports that not all rabbits respond to this treatment and it is common that some head tilt will remain. Some breeders have also tried other steroids and have seen rapid improvement within days. It may be beneficial for breeders to have the rabbit tested for exposure to E. cuniculi and if positive try the steroid treatment first.
I also found some newer articles and mailing list posts about treatment for E. cuniculi that may be of interest to all of us. "The encouraging finding is that we have also had rabbits with clinical signs and positive E. cuniculi titers who have shown improvement in their clinical signs when treated with albendazole." 4 For rabbits who titer positive for E. cuniculi and suffer from progressive paralysis: "Treatment: Do better on tetracycline (arrests or slows progression, may improve a little). In drinking water: 500 mg/liter." 5 A pet owner on a mailing list reported using Oxibendazole and posted "In the past, there wasn't a lot of point in running titers b/c you couldn't do anything about the parasite anyway. Now, we can, so to me it's worth it. Truthfully, I think that from now on I will probably titer all rabbits entering my home. Oxibendazole (Anthelcide EQ-Pfizer) is inexpensive and easy to get over the counter, so I will probably treat ALL rabbits who titer for it regardless of whether they exhibit symptoms." 1
Now comes the tricky part about E.cuniculi and something we as breeders need to watch, more vets are suggesting their rabbit clients test for exposure to E. cuniculi since it may affect the rabbit later in life. How to treat a positive rabbit not exhibiting signs is at this point controversial. The question all rabbit fanciers and the veterinary community need to answer is how prevalent is E. cuniculi and do we really need to test and treat for it. Don't think this is easy to answer, the above treatments I listed are being used on rabbits who test positive for exposure to E. cuniculi and are exhibiting signs of neurological problems. Teselle's post about now testing and treating all her animals got this response "I am a pharmacologist, I don't take aspirin if I don't really have a splitting headache. Oxibendazole is in my opinion a safe drug, but since this is an experimental procedure, that does not mean it will not harm your rabbit. Considering the length of time on the drug, and the lack of solid studies (that may never happen, so it will be done as a clinical experience situation) giving this drug to all rabbits without documentation of the disease is inappropriate and possibly dangerous to the health of your bunny." 2
Why should breeders worry? "Because the disease is transmitted vertically (from mother to offspring), the testing of breeding animals is especially important. Pet shops and rabbit shows could contribute to the end of this disease by insisting that only serologically negative animals be sold or exhibited. The House Rabbit Society could help by insisting that serologically positive rabbits be adopted to homes without rabbits or to homes with other seropositive pets." 3 At this point the only control method for eliminating E. cuniculi is a "Test and removal" method. 6 What this means is the breeder tests their herd and animals with positive results to E. cuniculi are removed from the herd. Testing would continue on a weekly basis until 3 negative tests and then go to quarterly or annual with all new animals entering the herd tested beforehand. I don't know what the costs involved with this is. And again you wrestle with what if some of your best breeding or show animals test positive. The decision to test or not to test may be taken out of our hands if the veterinary community and rabbit activists begin insisting that all pet rabbits be tested as part of a routine exam.
I ask these questions because from what I have read it does not appear that E. cuniculi is causing widespread disease problems to warrant test and removal from breeding herd or to impose show rules. How would the latter even be possible? Here are some more quotes to ponder:
"The majority of rabbits who are infected by this organism show no clinical signs of illness. Occasionally infected rabbits may exhibit neurological signs, including those listed above. There have been no thorough studies of pet rabbits with neurological disease to show what proportion of those rabbits may be infected with E. cuniculi. Historically it has been thought to only rarely cause disease, however popular thinking in pet rabbit circles is that clinically ill rabbits may be common. The statistics in the literature for the disease are based on the incidence in laboratory rabbits; pet rabbits may have a much greater rate of infection."3
"Incidence of infection in commercial rabbit colonies has been reported to range from 17 to 76% unless special efforts have been made to exclude this infection. The incidence of infection in pet rabbits, as determined by serologic testing at the University of Missouri in 1995 and 1996, was about 41%. This data suggests that E. cuniculi is a relatively common infection in pet rabbits, and may be responsible for contributing to disease not well-described in the companion animal literature." 6
"And always remember that E. cuniculi is not the first disease to check. It is somewhere near the end of the list. Statisticly speaking (at this time) E. cuniculi is not as common as some other problems that can cause the same symptoms." 2
"Of the "clinically normal" (healthy) rabbits tested (whose results have returned), 11 of 25 rabbits (44%) had significantly high titers. This tells us that they have or have had the parasite. We also found several rabbits with neurological abnormalities, ranging from vestibular disease (torticollis/head tilt) to paralysis or paresis (loss of neurological function), with positive titers." 4
"Whether serologically positive rabbits without signs of disease should be treated is controversial. At this time we are recommending that these rabbits be tested periodically. Rabbits with a rising titer or those that develop clinical signs (head tilt, etc.) we will recommend treatment."4
Footnotes
1) Elizabeth Teselle Post Etherbun
2) George Flentke Etherbun post
3) E. Cuniculi: Cause of Unexplained Neurological Diseases? By Jeffrey Jenkins DVM
4) Update on Testing and Treatment of Rabbits with E. Cuniculi By Jeffrey Jenkins DVM
5) "Rabbits Physical Exam and Differential Diagnoses" by Carolynn Harvey DVM 1997 vet conference
6) Encephalitozoon cuniculi: An Update on Epidemiology, Diagnosis and Control of the Disease" Cynthia Besch-Williford DVM PhD 1997 vet conference
