Ophthalmopathies in Dogs with Visceral Leishmaniasis - Treatment with Allopurinol and Diagnosis by qPCR and Cytology
Authors: Sávio Matheus de Carvalho  , Kellen Matuzzy Silva de Melo  , Társia Giabardo Silva Mendonça  , Luana Dias de Moura  , Elyse Medeiros Olimpio Bomfim  , Jackellyne Geórgia Dutra e Silva Leite  , Felipe Araújo de Mendonça  , Maria do Socorro Pires e Cruz  
Published: December 2024

Background: Canine visceral leishmaniasis (CVL) is an infectious parasitic zoonotic disease endemic to several countries. Among the most common clinical symptoms of CVL are eye symptoms. The association between clinical, epidemiological and laboratory tests (e.g., serological and molecular tests) provides a definitive diagnosis, and the disease is treated with leishmaniostatic and leishmanicidal drugs. Various diagnostic techniques stand out, among them, polymerase chain reaction (PCR) and conjunctival cytology. This paper describes the main ophthalmopathies in dogs affected by CVL, treated with allopurinol, and the detection of the protozoan by cytology and conjunctival swab PCR.Materials, Methods & Results: This study involved 16 dogs treated with allopurinol and 6 dogs without treatment. Bone marrow aspirates were obtained from the sternum and popliteal lymph node. Samples for conjunctival qPCR were collected from both eyes of each animal, using a sterile swab. The animals underwent complete ophthalmic examination using halogen lighting, magnifying loupe, fundoscopy, and occasionally, direct ophthalmoscopy. Tests were also performed to assess tear production, intraocular pressure, ocular reflexes and the presence of corneal ulcers. Slides prepared for cytology were stained and DNA was extracted and stored for qPCR testing to estimate the parasite burden (PB). The collected data were then subjected to a qualitative analysis. Ophthalmic changes were found in 13 of the 16 treated animals (81.25%) and in 3 of the 6 animals not treated with allopurinol (50%). Sixteen of the 22 dogs (73%) were clinically symptomatic, showing 1 to 5 concurrent ocular clinical signs. Uveitis was the most common ocular condition and was detected in all the dogs with some form of ophthalmopathy. Corneal edema (31.25%; n = 5), keratoconjunctivitis sicca (25%;n = 4), periocular dermatitis (25%; n = 4), blepharitis (25%; n = 4) cataracts (18.75%; n = 3), and to a lesser extent, glaucoma, corneal ulcer, and 3rd eyelid prolapse (6.25%; n = 1 each), were also found. No Leishmania spp. amastigotes were identified by conjunctival cytology in any sample. The conjunctival swab qPCR revealed 19 dogs (86.36%) positive for CVL, most of them (37%; n = 7) with a PB of 3001 to 6500 copies of Leishmania spp. DNA. Among the dogs treated with allopurinol, 68.4% (n = 13) were PCR positive for CVL and most of them showed a PB of 955 to 3,000 copies of the parasite’s DNA. Among the symptomatic dogs, the highest PB was detected in a dog with only 2 ocular disorders, while the lowest PB was found in the dog with the most numerous ocular disorders.Discussion: Among the ocular changes found here, the higher frequency of uveitis is consistent with those reported for dogs with CVL. The high rate of ophthalmopathies in treated animals can be attributed to the leishmaniostatic rather than leishmanicidal nature of allopurinol, which, as a monotherapy, does not completely eliminate the parasite from the dog’s organism. The frequency of ophthalmic alterations observed in this study is compatible with that described in symptomatic and CVL positive dogs, both treated and untreated. The non-exfoliative collection method of conjunctival cytology may have generated false negative results. Conjunctival swab qPCR is able to detect Leishmania spp. DNA in dogs with and without ophthalmic alterations, but PB quantification may vary depending on the primers used. Although the number of ocular alterations is expected to be higher in animals with higher PB, in this study, dogs with higher PB did not necessarily exhibit more ophthalmic disorders. Conjunctival swab qPCR was more effective than conjunctival cytology for diagnosing CVL, even in dogs treated with allopurinol. As a monotherapy, allopurinol favors clinical improvement in dogs, but ocular lesions may persist, regardless of the conjunctival PB.
Keywords: Leishmania, dog, eye, conjunctiva.
Título: Oftalmopatias em cães com leishmaniose visceral - tratamento com Alopurinol e diagnóstico por qPCR e citologia
Descritores: Leishmania, cão, olho, conjuntiva