Toxoplasmosis in Dogs: New Ocular Manifestations and Diagnostic Challenges
A recent case series highlights the underrecognized role of Toxoplasma gondii in causing ocular inflammation in dogs, with findings that challenge previous assumptions about the disease's prevalence and presentation in…
A 5-dog case series published in *Veterinary Parasitology: Regional Studies and Reports* details ocular signs ranging from blepharitis to retinal detachment and blindness in dogs suspected of having active toxoplasmosis. The study, conducted at the Hebrew University Veterinary Teaching Hospital in Jerusalem, Israel, found that ocular toxoplasmosis is rarely reported in dogs, likely due to nonspecific symptoms leading to underdiagnosis (¹). The dogs presented with a range of ocular diseases, including bilateral anterior uveitis, unilateral panuveitis with retinal detachment, and bilateral panuveitis with partial retinal detachment and acute blindness (¹). [1]
Concurrent systemic conditions were common among the affected dogs, with one receiving immunosuppressive prednisone for immune-mediated thrombocytopenia, one having visceral leishmaniasis, and another being later diagnosed with hepatic and splenic masses. The authors suggest that immunosuppression, a known trigger in humans and cats, may similarly predispose dogs to toxoplasmosis (¹). The Weimaraner in the study initially improved with clindamycin and corticosteroids but later relapsed with severe bilateral blepharitis and keratoconjunctivitis, despite treatment discontinuation (¹). [1]
All five dogs received oral clindamycin and topical prednisolone acetate, with initial improvement in most cases. However, two dogs relapsed despite prolonged antimicrobial therapy. One relapsed after switching from a compounded veterinary formulation of clindamycin to a commercial human formulation, raising concerns about the variability of compounded medications (¹). The study highlights the limitations of relying solely on IgG titers for diagnosing active infection and suggests the use of aqueous humor PCR and the Goldmann-Witmer coefficient to improve diagnostic accuracy (¹). [1]
The authors conclude that toxoplasmosis should be considered in dogs with uveitis or chorioretinitis, especially those that are systemically ill or immunocompromised. They emphasize the need for long-term monitoring and extended treatment in some cases and call for larger prospective studies to refine diagnostic approaches and treatment regimens (¹). [1]
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The case series was conducted at the Hebrew University Veterinary Teaching Hospital in Jerusalem, Israel, between January 2023 and December 2025. The study included five dogs, ranging in age from 3.5 to 8 years, with four being mixed breed and one a Weimaraner. The dogs were evaluated based on ocular disease, a positive anti–T. gondii IgG titer at presentation, at least one positive follow-up serologic result, and at least one ophthalmologic reexamination. The study highlights the rarity of ocular toxoplasmosis in dogs, possibly due to underdiagnosis stemming from the nonspecific nature of the symptoms. The scope of the study involved a retrospective review of medical records and focused on identifying ocular manifestations associated with active toxoplasmosis in dogs. [1]
The five dogs presented with a variety of ocular conditions, including bilateral anterior uveitis, unilateral panuveitis with retinal detachment and blindness, and bilateral panuveitis with partial retinal detachment and acute blindness. One of the dogs had an enucleated eye due to secondary glaucoma. Initial anti–T. gondii IgG titers, measured by indirect fluorescent antibody test, ranged from 1:256 to 1:1024, with a cutoff of ≥1:64. Follow-up results showed that three dogs had a 4-fold titer increase, consistent with seroconversion, while the remaining two had persistently high titers suggesting active infection. The study emphasizes the role of immunosuppression in predisposing dogs to toxoplasmosis, as seen in dogs with conditions such as immune-mediated thrombocytopenia, visceral leishmaniasis, atopic dermatitis, and hepatic and splenic masses. [1]
The Weimaraner presented with fever, lethargy, and bilateral anterior uveitis, and initially improved with clindamycin and corticosteroids. However, after discontinuation of clindamycin, the dog relapsed with severe bilateral blepharitis and keratoconjunctivitis, along with rising C-reactive protein (CRP) concentrations and anti–T. gondii titers. Alternative therapies, including trimethoprim-sulfamethoxazole and atovaquone, were ineffective due to adverse reactions. Another dog relapsed after switching from a compounded veterinary clindamycin formulation to a commercial human formulation, highlighting concerns about variability in compounded medications. The study notes that while all dogs initially responded to treatment, two experienced relapses despite prolonged antimicrobial therapy. [1]
The study acknowledges limitations, including the small sample size, retrospective design, and reliance on IgG titers and clinical response rather than definitive confirmatory tests such as PCR, histopathology, or IgM titers. The authors suggest that aqueous humor PCR and the Goldmann-Witmer coefficient can improve diagnostic accuracy and that PCR from Schirmer tear test strips may offer a noninvasive alternative in human medicine. They emphasize the need for larger prospective studies to further explore diagnostics, treatment regimens, and long-term outcomes in dogs with ocular toxoplasmosis. The findings underscore the importance of considering toxoplasmosis in dogs with uveitis or chorioretinitis, particularly those with systemic illness or immunosuppression, and advocate for long-term monitoring and extended treatment when necessary. [1]
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