Hi!
I’m sorry Sky is unwell.
The parasite your gp has researched is called encephalitozoan cuniculi, e cuniculi or EC for short. It is a microscopic (microsprodian) parasite, so not an actual animal like a worm or a mite.
It is a parasite that many rabbits carry, they can contract in their mother’s womb. Most rabbits dont get sick from it, but some rabbits do get sick. Why this is, isnt fully understood. One, rather persuasive theory is that the parasite is opportunistic and seizes the opportunity to multiply when the rabbit’s immune defense is lowered for some reason. A rabbit’s immune defense can be weakened by many different things, ranging from a seasonal moult to environmental stress to old age or an infection. E C also by itself takes a toll on the immune defense.
EC is mostly known to cause neurological issues like head tilt or hind end weakness. It can however attack other organs than the brain and nervous system, especially the kidneys. The heart and the GI system can be affected too. EC is probably rather widely under-diagnosed.
There are tests for EC, but none of them are very good. Here is some info on EC diagnosing an testing from The Swedish Uni of Agricultural Sciences, scroll down for English text:
https://stud.epsilon.slu.se/7847/
Treatment can be started right away without waiting for the tests to come back. Some vets will treat on clinical diagnosis only, without doing tests. Standard treatment is a 28-day course fenbendazole,a de-wormer sold under the brand name Panacur. This med can be combined with the antibiotic Baytril, which has been shown to have some additional effect on EC. Metacam (meloxicam) for inflammation and pain is also as a rule given, because ec causes infkammation. Rabbits are very sensitive to corticosteroids, so cortisone is often best avoided, but may be used in severe cases as a single shot.
If you have other rabbit together with Sky, they have all been exposed to the parasite. There is no veterinary consensus about treating he sick bun’s companion rabbits unless they have tested positive or developped symptoms. Some vets will however prescribe a 9 day course of fenbendazole for asymptomatic buns.