What is Encephalitozoon cuniculi (E.C.) in rabbits

Encephalitozoonosis is a parasitic disease known by various other names. Among rabbit owners it is simply called E. cuniculi or E.C. for short, also stargazer disease, crooked head disease, head tilt or torticollis are used to refer to this rabbit disease.

The trigger of this disease with the characteristic head tilt is a parasite, but more than half of all domestic rabbits have antibodies against E. cuniculi, i.e. they carry the parasite without ever showing symptoms. Experts then speak of a latent infection.

E.cuniculi – a fungus-like parasite is responsible

Encephalitozoon cuniculi is a protozoan, a single-celled organism that occurs only within a more highly developed cell. It belongs to the microsporidia and is thus a representative of the fungal kingdom.

In its host, it occurs preferentially in the area of the central nervous system or in the kidneys, where it settles and causes damage.

The pathogen itself can be divided into three strains, which inhabit their preferred hosts according to type:

Type I, it refers to the rabbit strain, which is pathogenic (causes disease) to rabbits, but also to humans.
Type II is called the mouse strain and also infects cats and foxes.
The canine strain, type III, has been found primarily in dogs, but also in prosimians.

In general, all types of E. cuniculi could also occur in rabbits, at least under laboratory conditions. However, only the rabbit type has been known to occur as a natural infection.

The disease was first described in 1922 by Wright and Craighead in the form of infectious spinal cord paralysis in young rabbits.
Origin of E. cuniculi in rabbits

Scientists have not yet been able to conclusively clarify the route of transmission. So far, the oral route of transmission via food contaminated with spores is certain. Infected animals excrete spores of E. cuniculi with their feces and urine, which are in turn ingested by other animals during feed intake. The spores enter the digestive tract and spread from the intestine through the bloodstream.

Fetal infection is also possible, with the fetus already becoming infected in utero. A striking feature of this transmission route is that no antibodies are detectable in the blood, since E. cuniculi is not recognized as an “invader” due to the early infection.

Other possible routes of transmission are under discussion.

Although a large proportion of rabbits carry the pathogen, most of them do not experience an outbreak of the disease. However, favoring factors can be observed that came into play in many rabbit patients in the run-up to an outbreak of the disease.

These include a high stress level, for example due to a move, loss of a partner or generally poor housing conditions. Advanced age or other concomitant diseases that weaken the immune system have also been observed in disease outbreaks.

However, torticollis can also break out without any recognizable triggers, or it does not break out even though the above-mentioned triggers are present. This makes the diagnosis for the veterinarian not necessarily easy. 

Symptoms of E. cuniculi in rabbits

E. cuniculi shows many faces and has typical symptoms, not least the head tilt, which has given the disease its name. Nevertheless, the diagnosis is extremely difficult, because many other diseases in rabbits are accompanied by similar symptoms and there is no “sure test” for E. cuniculi.

Encephalitozoonosis can only be diagnosed with certainty after death by post-mortem examination; in living rabbits, the veterinarian can only make tentative diagnoses according to the exclusion procedure.

Among the indicative symptoms are signs of failure of the extremities, especially the hind legs and various types of paralysis, which may occur only briefly and then disappear. Also purulent discharge from eyes and/or nose, eye tremor and renal insufficiency show the clinical picture of E. cuniculi.

The typical head obliquity shows up only slightly, especially in the early stages of the disease, to continue to a grotesque twisting of the head as the disease progresses. In some cases there is also hyperextension of the head, hence the name stargazer’s disease.

At the onset of the disease, hoppers simply appear a bit clumsy, falling over when preening or not sure on their feet when mating.

As the disease progresses, they lose their sense of direction and can no longer walk in a straight line, sometimes spinning around their own body axis as if upside down. Epileptic seizures with simple staring, as if the long ears have stepped away, may occur, as well as twitching of all extremities. Perception may also be disturbed, up to total loss of senses. Food is refused, and the rabbits are deaf and blind.
Treatment of crooked head disease in rabbits

Treatment is symptomatic and antiparasitic. The administration of an appropriate anthelmintic, in this case with the active ingredient fenbendazole or albendazole, is intended to kill the pathogens, at least in the intestine, and thus prevent further spread. However, complete elimination of Encephalitozoon cuniculi is not possible.

If the body is already visibly damaged by the infection (failure symptoms, infections, kidney problems), many veterinarians place the long-eared patient under antibiotics. However, cortisone should not be administered, as this only leads to a short-term improvement in the symptoms, but places an enormous strain on the weakened organism and does not benefit the recovery process.

To protect the nerves and prevent further damage, the administration of vitamins from the B-complex (B1, B6, B9 and B12) has proven effective. As an accompanying therapy, herbs to strengthen the immune system and for detoxification have proven effective (nettle, birch, sharp fork, dandelion, chamomile, fennel, hogweed, etc.).

If the animal patient can no longer take in food and water by himself, force-feeding is also necessary.

In case of kidney problems, fluid intake via infusion may be considered.

The chances of recovery are quite different depending on the onset of therapy. If the therapy is started early, the symptoms are completely cured. Spontaneous healing of E. cuniculi may also occur. In some cases, however, permanent damage is to be expected, as well as such massive (nerve) damage that the long-eared animal has to be put down.

In the meantime, it is not recommended to separate infected animals from the herd, as this leads to increased stress situations and is not conducive to healing. Stress in any form should be kept away from the diseased animals in any case, especially with regard to the separation of diseased rabbits.

In this context, it should be borne in mind that the high infestation rate is disproportionate to the few E. cuniculi outbreaks. This suggests that the mere presence of the pathogen does not lead to an outbreak of the disease and, consequently, separation of sick and healthy animals is unnecessary.

Prevention of infection with E. cuniculi

The optimal prevention is a healthy, happy rabbit. To achieve this, the housing conditions must be just as correct as the species-appropriate, varied diet.

Stress is also one of the possible triggers of an infection with E.cuniculi, or an outbreak of the disease. Since stressful situations cannot be avoided in every rabbit’s life, a preventive administration of an anthelmintic can be considered during this time. Fenbendazole is the drug of choice.

Likewise, anthelmintic herbs (thyme, tansy, mugwort, blueberries, leeks, etc.) can be beneficial to intestinal health and strengthen the immune system.

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