Encephalitozoonosis in pet rabbits (Oryctolagus cuniculus): pathohistological findings in animals with latent infection versus clinical manifestation.

Encephalitozoon cuniculi is a common infectious agent of rabbits. The aim of this study was to determine the distribution and extent of histological lesions in the brain and in the kidney of naturally infected pet rabbits with or without clinical encephalitozoonosis. In 71 animals (33 with symptoms) which died or were euthanised, histopathological examination including staining of spores (Ziehl-Neelsen, acid-fast trichrome) was performed and changes were described quantitatively. The cerebrum was the most frequently affected brain region (97.5%), whilst the cerebellum (55%) and the vestibular cores (37.5%) were less commonly concerned. Granulomas were found in 77.5% of animals with encephalitis and in 12.5% of rabbits with interstitial nephritis. Although cerebral granulomas were found irrespective of the grade of histological changes, they were significantly correlated with changes at higher grades. There was no correlation between the severity of encephalitis and neurological symptoms. Since severe lesions were also found in clinically inconspicuous animals, histological findings of inflammatory lesions are not indicative of overt encephalitozoonosis as the causative agent for neurological signs. Other diseases causing neurological symptoms, such as suppurative encephalitis, otitis media as well as malignant lymphoma were also detected in the rabbit population that was examined in the present study.