Dr Vesela Elenkova – master scintific in veterinary ophthalmology and surgery, veterinary clinic “Eskovet”– Bulgaria, Sofia
Case presentation :
A nine month female rabbit presented for a right eye lesion of two weeks duration. There was cataract on the same eye from birth. The referring veterinarian had prescribed a course of topical and systemic antibiotics but it continued to deteriorate. The eye was become very painful. The lesion appeared as a whitish-yellow mass into the hyperemic iris, slightly protruding into the anterior chamber. There was a mature cataract formation and the pupil was mydriatic with no response to light. The intraocular pressure (IOP) of the affected eye was 40. On the other was 11and it was not clamped. Fluorescein staining was negative for corneal lesions on both eyes. On the ultrasound examination there was no changes into the posterior segment of the affected eye.
There was only seen the hyperechogenic lens and the lesion in the iris. The rabbit was in pain when touched and didn’t want to eat well.
The patient history and appearance of the lesion were compatible with Encephalitozoon cuniculi-induced phacoclastic uveitis, and a tentative diagnosis was made. Other diagnostic defferentials included granuloma caused by Pasteurella or other bacterial infections, but they were unlikely considering cataract formation. Diagnostic included complete blood count, biochemical profile and serology testing.
The complete blood count and serum biochemical profile were within normal limits. The serum IgG-antibodies were not so high, but the IgM-antibodies indicate active infection in most cases. They bought are not indicative for utero infection.
We opted medical management. Except of the antibiotic therapy (with enrofloxacin PO and ciprofloxacin eye drops), the treatment was continued with fenbendazole at 20 mg/kg PO q24h for 28 days. Prednisolone acetate ophthalmic drops were prescribed to treat the uveitis and dorzolamide hydrochloride and timolol maleate drops for the eye pressure.
After 1-week recheck, the lesion had not changed, hyperemia was decreased, the IOP had become low – 6. There was no pain in the eye and the rabbit was doing well. The pupil still does not respond to light. After 2 weeks more, there was no change. The rabbit was in very good condition, but the vision in the right eye was compromised. Surgery might be necessary in the future depending on progression of the lesion, discomfort, and long term effects on the eye.
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 recognized zoonosis, 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. 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. Most of the time, these organisms do not cause any obvious clinical disease. When E. cuniculi reach nerve tissue, rabbits can experience neurologic impairment, characterized by partial or complete paralysis, loss of coordination, seizures and head tilting.
E.cuniculi-assosiated phacoclastic uveitis is recognized in rabbits. There is no sex predisposition and the condition is often seen in younger rabbits. The mechanism by which the protozoan causes cataract is unclear in detail, but its lifecycle gives clues as to aetiopathogenesis of cataract. Passage of parasite between adult and young happen in utero with the parasite circulating in the fetus and sometimes ending up residing in the developing lens. The parasite migrates through the anterior lens capsule causing liberation of lens protein into the iris and anterior chamber and subsequent development of lens-induced uveitis, however, the posterior chamber usually remains unaffected. Normally this uveitis presents as a white-yellow mass in or near the pupil, sometimes with neovascularisation rendering it red or pink.
Serum ELISA antibody titers are helpful in making a diagnosis, however, serology only indicates past exposure and is not diagnostic of or necessarily correlated with clinical disease and infection. Immunofluorescence assay and polymerase chain reaction (PCR) testing of tissue, urine and feces samples, as well as cerebrospinal fluid and removed lens material. These test looks for antigens, unlike serology, which test for antibodies. Simultaneous testing of IgG and IgM-specific antibodies can give an indication of infection status because IgM antibodies indicate active infection. If transmission is transplacental, bought IgG and IgM antibodies may be low.
In this cases treatment options include antiprotozoal medication, topical corticosteroids for the uveitis, surgery to remove the affected lens and granuloma if it is possible. The other option is enucleation, but it is not common if the eye is functional, because it is unlikely to eradicate the infection. In other cases the eye may atrophy without surgery (phthisis bulbi).
E.cuniculi-assosiated phacoclastic uveitis should be always suspected for rabbits presenting with ocular lesions and uveitis and oral antiprotozoal medications are always recommended, as affected rabbits may develop infection in the brain and encephalitis, that can lead to death.