Encephalitozoon cuniculi

Encephalitozoon cuniculi was virtually unrecognised as a cause of disease in pet rabbits until a few years ago. Nowadays it is much more widely diagnosed amongst pet rabbits, with owners of affected rabbits wanting to learn as much as possible in order to give their rabbits the best care possible. However, the disease isn’t a straightforward one, and there is still a lot that we don’t understand about it, so it does take some explaining in order to understand what it is, what it does and how it is currently treated.

Encephalitozoon cuniculi (E. cuniculi) is a protozoal parasite. The parasite primarily affects rabbits, but cases have been reported in sheep, goats, dogs, cats, monkeys, guinea pigs, foxes, pigs and humans. It is a recognised zoonosis (can be transmitted to humans), but the zoonotic risk seems to be minimal to healthy individuals observing basic hygiene and to date there have been no reported cases of direct transmission from a rabbit to a human. However, those individuals who are immunosuppressed should implement strict hygiene and if possible avoid animals suspected or confirmed of being infected with E. cuniculi and undoubtedly seek medical advice from their doctor.

Spores are shed in infected animals urine and transmission is usually by ingestion of contaminated food or water, or less commonly by inhalation of spores. Transmission from mother to young (transplacental) also occurs so that offspring are born infected.

One study* has shown that approximately 52% of healthy rabbits in the UK carry the parasite, but many never show any clinical signs. We still dont understand why some infected rabbits develop the disease and others dont, but it is most likely that it is related to their immune function.

If the rabbit is infected with E. cuniculi and showing clinical signs then it may exhibit any, some or all of the following:

  • Hindlimb paresis (weakness of the hindlimbs)
  • Torticollis (head tilt)
  • Paralysis
  • Urinary incontinence and/or scalding
  • Tremors
  • Cataracts and lens-induced uveitis
  • Collapse
  • Renal failure
  • Death

These clinical signs are caused by the body’s inflammatory reaction to rupture infected cells, mainly in the nervous system and kidney. However, many of these symptoms can be associated with other disease processes, so a diagnosis is rarely made on clinical symptoms alone.

* Keeble E J & Shaw D J (2006) Seroprevalence of antibodies to Encephalitozoon cuniculi in domestic rabbits in the United Kingdom. Vet Rec 158(16), 539-544 www.ncbi.nlm.nih.gov/pubmed/16632526.

If the rabbit is showing clinical signs that may be indicative of an E. cuniculi infection, then your vet will probably recommend a blood test.

Nowadays the test most commonly used is the ELISA test that measures serum antibody levels. This detects whether the rabbit has been exposed to the parasite.

A blood sample will be taken from your rabbit and sent away to a laboratory. A negative result is generally conclusive and can rule out E. cuniculi as the problem, unless the sample is taken very early on in infection or the immune system is so weak that the rabbit doesn’t produce antibodies. A positive result isn’t always that straightforward. A high antibody titre, together with clinical signs is usually enough for most vets to commence the rabbit on treatment for E. cuniculi, but a moderate or low antibody titre may not be enough for the vet to be sure that E. cuniculi is the problem since so many rabbits carry the parasite without symptoms (asymptomatically).

In these cases diagnosis is usually made by taking a further blood sample a few weeks later and if the titre is higher than the first (a rising titre) this would indicate an active infection and would usually lead to a diagnosis of E. cuniculi as the problem.

Another available test is the PCR test, which detects the parasite itself, usually in a urine sample. A positive result means that the rabbit is shedding the parasite and is thus infected, but a negative may mean either that the rabbit is not infected, or that it is infected but just not shedding spores at that time.

Treatment aims to reduce inflammation and prevent formation of spores. If a diagnosis is made or clinical symptoms indicate E. cuniculi to be the cause of disease then a 28-day course of oral fenbendazole, e.g. Panacur®, at 20 mg/kg once a day is the general treatment of choice, plus anti-inflammatory drugs such as corticosteroids.

However, many new treatments are being trialled and looked into, so your vet may decide to treat with a different drug or combination of drugs.

If a secondary bacterial infection is also present, then the treatment regime will probably also include antibiotics.

This is where people differ in their opinions. Routinely (prophylatically) treating against E. cuniculi is recommended by some vets but deemed pointless by others!

Some vets feel that treating your rabbit 2-4 times a year can help reduce the incidence of E. cuniculi developing to a point where clinical signs are seen. However, other vets feel that preventive treatment is pointless because as soon as the course of treatment is finished the rabbit is no more protected than it would have been if it hadn’t been treated. This is an area where more research is needed.

If you chose to use preventive treatment then there are products that are licensed for this purpose. It is usually a 9-day oral course given once daily at the same dose as what would be used to treat an infected rabbit (20 mg/kg) and can be done every 3-6 months.

Please contact your vet who will be happy to advise you.

We don’t really know. One study show that a 28 day course of fenbendazole does eliminate the parasite, but this may not be the case with all rabbits and some people feel that once a rabbit is infected with E. cuniculi it will be a life-long carrier. The disease process will generally take one of the following routes:

Treatment improves the clinical signs

If this is the case then after 28 days the treatment is usually stopped. At this point if the rabbit deteriorates again then treatment can be recommenced. It isn’t known for sure what triggers a flare-up of the disease but stress is thought to play a part or if the rabbits immune system is weakened by another disease and can no longer keep the parasite at bay. Also don’t forget that a rabbit can become re-infected if it is exposed again to spores from the environment.

Some rabbits need lifelong medications, whereas others need it sporadically to control clinical signs when they manifest themselves. Others only need a one off treatment course and never seem to develop clinical signs again. However it should be stated that treatment might not be sufficient for the rabbit to make a full recovery and some level of clinical signs often continue.

Treatment does not improve the clinical signs

Generally if treatment is going to work then some improvement in clinical signs is seen in the first week or so, with a gradual improvement.

For those rabbits that fail to improve then euthanasia is the only humane option if the clinical signs are debilitating and the rabbit has no quality of life.

Firstly you need to be 100% sure that the rabbit isnt already carrying the parasite. Ask your vet if they would be willing to blood test your rabbit.

If the result comes back as negative, then the best form of defence is to stop your rabbit coming into contact with any other rabbits, be this domestic or wild. As previously mentioned spores from the parasite are primarily passed on in the urine of infected rabbits so removing this route of transmission is your rabbits best form of defence. Good hygiene is vital as spores can easily be killed by routine disinfectants.

E. cuniculi is a parasite and not a virus, therefore there is no vaccine against E. cuniculi.

This depends upon the rabbit’s response to treatment, and the frequency and severity of any flare-ups.

Generally speaking, a lot of rabbits who develop problems due to E. cuniculi can go on to do well and lead full lives, but treatment needs to be prompt, otherwise the parasite will cause more damage and clinical signs will be more severe.

Quality of life

It is important to keep in your mind your rabbits quality of life when dealing with E. cuniculi. For example if your rabbit has a head tilt but is otherwise eating, drinking and managing to get around, then the rabbit is probably perfectly happy. Rabbits don’t worry about what they look like; this is more of a concern to the owner.

Whereas a rabbit that is continually scalded with urine, miserable, rolling/falling over or unable to move due to hind limb weakness or paralysis is not a happy rabbit and you should think seriously about if your rabbit has an acceptable quality of life.