A parasite best known for infecting cats may also be putting dogs' eyesight at risk. A new study documented five dogs with eye disease linked to suspected toxoplasmosis, including cases of retinal detachment and blindness. The findings reveal an overlooked veterinary concern and highlight the importance of recognizing and treating potentially sight-threatening infections.

A parasitic infection commonly associated with cats may be associated with severe, potentially sight-threatening ocular disease in dogs, according to a new study by researchers at the Hebrew University of Jerusalem.

The research, by the ophthalmology department of the university's Koret School of Veterinary Medicine, found that Toxoplasma gondii, a widespread microscopic parasite, may be associated with serious eye disease in dogs, ranging from mild inflammation to retinal detachment and irreversible blindness.

Published in Veterinary Parasitology: Regional Studies and Reports, the findings highlight an underrecognized condition and suggest that veterinarians should consider toxoplasmosis when examining dogs with unexplained ocular inflammation.

A parasite better known for infecting cats
Toxoplasma gondii is one of the world's most widespread parasites, capable of infecting humans and numerous animal species. Although cats are its definitive hosts, other animals, including dogs, can become infected.

While toxoplasmosis is a recognized cause of eye disease in humans and cats, its ocular manifestations in dogs remain poorly understood.

To investigate this gap, Dr. Yamit Soueid and an Ophtho team in collaboration with Prof. Itamar Aroch at the Hebrew University Veterinary Teaching Hospital examined the medical records of five dogs treated at the Hebrew University Veterinary Teaching Hospital in Rehovot between 2023 and 2025.

All five had eye abnormalities accompanied by positive blood tests for antibodies against the parasite. In three dogs, repeated testing demonstrated a fourfold increase in antibody levels, supporting recent or active infection.

The severity of the disease varied considerably. Some dogs developed inflammation in the front of the eye, while others experienced extensive inflammation, retinal detachment and blindness.

In one particularly severe case, a six-year-old dog developed irreversible blindness and glaucoma, and the affected eye was subsequently surgically removed.

Another dog, which initially presented with sudden blindness in both eyes, regained its vision following treatment, although lasting retinal changes were subsequently documented.

An unexpected sign of infection
One particularly unusual finding involved an eight-year-old Weimaraner that developed severe eyelid inflammation, known as blepharitis, following an initial episode of ocular inflammation.

To the researchers' knowledge, this may represent the first reported association between severe blepharitis and suspected ocular toxoplasmosis in dogs, expanding the range of clinical signs potentially linked to the parasite.

"Most people associate toxoplasmosis with cats, but our findings suggest that dogs can also develop serious, potentially sight-threatening eye disease linked to this parasite," said Dr. Soueid.

"Greater awareness among veterinarians is important, particularly when treating dogs with unexplained eye inflammation or underlying medical conditions."

Treatment challenges and possible relapses

All five dogs showed initial clinical improvement following systemic clindamycin therapy, used to treat toxoplasmosis, alongside treatment to control ocular inflammation.

However, two dogs subsequently experienced recurrent ocular inflammation with persistently high antibody titers despite prolonged systemic treatment, highlighting the challenges of managing the disease.
Several dogs also had underlying medical conditions or histories of immunosuppressive treatment, raising the possibility that immune compromise may contribute to clinically significant infection, although this small case series cannot establish risk factors.

The researchers emphasized that diagnosing ocular toxoplasmosis remains difficult because its symptoms resemble those of other eye diseases, and positive antibody tests alone cannot establish that the parasite is responsible.

Why the findings matter
Although the study included only five dogs, it adds important evidence to the limited scientific literature on ocular toxoplasmosis in dogs.

The findings underscore the importance of considering the parasite in dogs presenting with unexplained eye inflammation, particularly those with underlying systemic illness or compromised immune systems.

For dog owners, marked eye redness, ocular discomfort or sudden changes in vision should prompt veterinary examination, as some ocular complications can result in permanent damage.

The researchers stress that larger studies are needed to improve diagnostic accuracy, establish effective treatment protocols and understand the risk of recurrence.