Toxoplasmosis may be an underrecognized cause of ocular inflammation in dogs

Toxoplasma gondii is a well-known cause of uveitis and chorioretinitis in cats, but a new case series suggests the parasite also belongs on the differential list for dogs with ocular inflammation.¹ Published in Veterinary Parasitology: Regional Studies and Reports, the report details 5 dogs with ocular disease suspected to be secondary to active toxoplasmosis. It also documents what the authors believe is the first description of blepharitis associated with the infection.

Ocular toxoplasmosis is rarely reported in dogs, possibly because its nonspecific signs lead to underdiagnosis, according to the investigators.¹

Case series details

Researchers retrospectively reviewed records of dogs presented to the ophthalmology and internal medicine services at the Hebrew University Veterinary Teaching Hospital in Jerusalem, Israel, between January 2023 and December 2025. Dogs were included if they had ocular disease, a positive anti–T gondii IgG titer at presentation, at least 1 positive follow-up serologic result, and at least 1 ophthalmologic reexamination.¹

The dogs ranged in age from 3.5 to 8 years; 4 were mixed breeds and 1 was a Weimaraner. Two dogs had bilateral anterior uveitis, 2 had unilateral panuveitis with retinal detachment and blindness, and 1 had bilateral panuveitis with partial retinal detachment and acute blindness. One blind eye was enucleated because of secondary glaucoma.¹

Initial IgG titers, measured by indirect fluorescent antibody test, ranged from 1:256 to 1:1024 (cutoff, ≥1:64). At recheck, 3 dogs showed a 4-fold titer increase consistent with seroconversion, and the remaining 2 had persistently high titers suggestive of active infection.¹

Comorbidities and immunosuppression

Concurrent systemic disease was common. One dog was receiving immunosuppressive prednisone for immune-mediated thrombocytopenia, 1 had visceral leishmaniasis, 1 had atopic dermatitis intermittently treated with oclacitinib, and 1 was later found to have hepatic and splenic masses. The authors suggest immunosuppression, a known trigger in humans and cats, may similarly predispose dogs.¹

A novel presentation

The Weimaraner initially presented with fever, lethargy, and bilateral anterior uveitis, and improved with clindamycin and corticosteroids. About 3 months after clindamycin was discontinued, however, she relapsed with severe bilateral blepharitis and keratoconjunctivitis but no intraocular inflammation, along with rising C-reactive protein (CRP) concentrations and anti–T gondii titers. An eyelid biopsy was declined, so alternative causes of the blepharitis could not be excluded.¹

Treatment and relapse

All 5 dogs received oral clindamycin, along with topical prednisolone acetate, and all initially improved. One dog with bilateral panuveitis regained vision within 2 weeks of starting treatment. Even so, 2 dogs relapsed despite extended antimicrobial therapy. In the Weimaraner, alternative therapies were also unsuccessful: trimethoprim-sulfamethoxazole was stopped because of a severe hypersensitivity reaction and atovaquone because of anorexia.¹

The second dog that relapsed had been switched from a compounded veterinary clindamycin formulation to a commercial human formulation after a suboptimal response. The authors caution that the timing of its later improvement does not establish causality, but they note that variability in compounded medications is a recognized concern.¹

Diagnostic challenges

A single IgG titer cannot distinguish active from latent infection, and T gondii–specific IgM testing was not available locally. The authors point to aqueous humor PCR and the Goldmann-Witmer coefficient as tools to improve diagnostic accuracy and note that PCR from Schirmer tear test strips has emerged as a noninvasive option in human medicine.¹

Limitations include the small sample size, retrospective design, and reliance on IgG titers and clinical response rather than definitive confirmatory testing such as PCR, histopathology, or IgM titers.¹

The authors conclude that toxoplasmosis should be considered in dogs with uveitis or chorioretinitis, especially those that are systemically ill or immunocompromised, and that long-term monitoring and extended treatment may be needed. They call for larger prospective studies focused on diagnostics, treatment regimens, and long-term outcomes.¹

Reference

1. Soueid Y, Ofri R, Sebbag L, Aroch I, Pe’er O. More than a feline disease: ocular manifestations in five dogs infected with Toxoplasma gondii. Vet Parasitol Reg Stud Reports. 2026;75:101590. doi:10.1016/j.vprsr.2026.101590