Unicellular parasite Encephalitozoon in hares

In the summer of 2018 two hares were identified with an infection of the parasite Encephalitozoon sp. This parasite is commonly seen in (domestic) rabbits, but little is known about its appearance in hares.

The parasite

Encephalitozoon is a spore-forming, unicellular parasite that is classified as part of the fungi kingdom. So far there are three different Encephalitozoon-species described: Encephalitozoon intestinalis, E. hellem, and, E. cuniculi (Hinney, 2016). E. cuniculi was already described in 1922-1923, but the other two species only in the beginning of the 90’s. Thanks to new techniques it was able to differentiate the spores, which wasn’t visible with a normal microscope.

General appearance

Encephalitozoon is common worldwide in numerous animals, both in a wide range of birds as mammals. But the different parasite-species do have a preference for certain animal groups. E. intestinalis is only described in mammals; E. hellem is described mainly in birds, although it was found in a few mammals and in a pet crocodile. E. cuniculi is mainly seen in domestic rabbits, but can also occur in numerous other animals such as birds and mammals.

Occurence in hares

In contrast to the information about the appearance of this parasite in domestic animals, there is little known about the appearance in wild living animals, and even less about the parasite in hares. In 2007, scientific literature described the first hare with a kidney disease that was caused by E. intestinalis and E. hellem (De Bosschere, 2007). The hare was an adult European hare, and the fifth one that had died within a month in the same area. The hare had a moderate to severe kidney inflammation. The presentation strongly resembled deviations similar to those caused by E. cuniculi in rabbits, but PCR-investigation found E. intestinalis and E. hellem.

Infection and signs

An infected animal releases spores in its urine. Through feed and water spores can get ingested by other animals. The parasite can also migrate from mother to offspring. Most infections proceed without clinical signs, but severe disease can occur. From domestic rabbits it is known that E. cuniculi can affect the kidneys and brain. Due to kidney impairment, rabbits will drink a lot. When the brains are impaired, the rabbit will show neurological signs such as a tilted head, paralysis, and balance disorders.

Hares submitted to DWHC

In June and July 2018, two dead hares were submitted to DWHC and Encephalitozoon sp. were detected. The exact species of Encephalitozoon can’t be determined without further testing. One hare was from the province of South Holland, the other from the province of Overijssel. The hare from the province of South Holland was a thin, pregnant doe (female hare). The hare from the province of Overijssel was a thin buck (male hare). Both animals had an inflammation caused by Encephalitozoon sp. and both animals had amyloidosis. Amyloidosis is a protein deposition disease and can cause organ failure. In hares amyloidosis is often the result of a chronic inflammation elsewhere in the body, and in these hares it is due to the inflammation by Encephalitozoon. In the buck these abnormalities were the cause of death, but in the doe the cause of death was shock.  The shock was created because the uterus was ruptured. This caused an inflammation in the peritoneum and the full-grown foetus to lay in the abdominal cavity. There was also a mummified foetus in the right uterine horn.

Every now and then in former years, spores of the Encephalitozoon sp. parasite, or the suspicion of infection with the parasite, was found in hares with (chronic kidney) inflammation. The issue with chronic inflammation is that the cause of disease, in this case the spores, is often not found. It is thus not always clear what the cause of chronic inflammation exactly is. That is why without further investigation is it not possible to say in how many hares this parasite was the cause of the inflammation.


Used literature:

De Bosschere, H., Z. Wang &P. A. Orlandi, 2007. First Diagnosis of Encephalitozoon intestinalis and E. Hellem in a European Brown Hare (Lepus europaeus) with Kidney Lesions. Zoonoses and public health, Volume 54, issue 3-4, May 2007, pages 131 – 134. https://doi.org/10.1111/j.1863-2378.2007.01034.x

Hinney B., B. Sak, A. Joachim & M. Kváč, 2016. More than a rabbit’s tale – Encephalitozoon spp. in wild mammals and birds. International Journal for Parasitology: Parasites and Wildlife, Volume 5, Issue 1, April 2016, Pages 76-87. https://doi.org/10.1016/j.ijppaw.2016.01.001

Scheelings, T. F., R. F. Slocombe, S. Crameri and S. Hair, 2015. Encephalitozoon hellem Infection in a Captive Juvenile Freshwater Crocodile (Crocodylus johnstoni). Journal of Comparative Pathology, Volume 153, Issue 4, November 2015, Pages 352-356