Parasite Usually Linked to Cats May Threaten Dogs’ Eyesight, New Study Warns
Researchers in Israel document five dogs with suspected ocular toxoplasmosis, including cases involving blindness, retinal detachment and recurring inflammation.
A microscopic parasite best known for infecting cats may also pose a serious threat to dogs’ eyesight. Researchers in Israel have documented five dogs with eye disease suspected to be associated with Toxoplasma gondii, including animals that developed retinal detachment and blindness. Although the study is small, its findings highlight a condition that veterinarians may not always consider when examining dogs with unexplained eye inflammation. The research also raises important questions about diagnosis, treatment and the possibility that some affected dogs may experience recurring problems even after initially improving.
A Familiar Parasite, but an Unusual Diagnosis
Toxoplasmosis is caused by Toxoplasma gondii, a microscopic parasite found worldwide. Cats are particularly important in its life cycle because they are the definitive hosts, meaning the parasite can reproduce sexually in their intestines. However, many other animals, including dogs and humans, can also become infected.
The infection is already recognised as a possible cause of eye disease in people and cats. In dogs, however, ocular toxoplasmosis has received considerably less scientific attention. This makes it difficult for veterinarians to determine how frequently the condition occurs, which symptoms are most characteristic and how reliably it can be diagnosed.
Researchers at the Hebrew University of Jerusalem’s Koret School of Veterinary Medicine decided to investigate this problem by examining the medical records of dogs treated at the university’s veterinary teaching hospital in Rehovot.
Their findings, published in Veterinary Parasitology: Regional Studies and Reports, suggest that toxoplasmosis deserves greater consideration when veterinarians encounter unexplained inflammation inside or around a dog’s eyes.
Five Dogs With Very Different Symptoms
The researchers examined five dogs treated between 2023 and 2025. All had eye abnormalities and blood tests showing antibodies against Toxoplasma gondii. In three dogs, repeated testing revealed a fourfold increase in antibody levels, providing additional evidence of recent or active infection.
The severity of the eye problems varied considerably. Some dogs developed relatively mild inflammation, while others experienced extensive inflammation affecting several structures inside the eye. The most serious complications included retinal detachment, glaucoma and blindness.
One six-year-old dog developed irreversible blindness and glaucoma in an affected eye. The damage was so severe that the eye eventually had to be surgically removed. Another dog initially lost vision in both eyes but regained its sight following treatment, although permanent changes to the retina remained.
These cases illustrate why early veterinary examination is important when a dog suddenly develops eye problems. Nevertheless, the researchers emphasise that the evidence does not establish that the parasite caused every abnormality observed.
An Unexpected Problem With the Eyelids
One particularly interesting case involved an eight-year-old Weimaraner. After an initial episode of eye inflammation, the dog developed severe blepharitis, a condition involving inflammation of the eyelids.
According to the researchers, this may represent the first reported association between severe blepharitis and suspected ocular toxoplasmosis in dogs. The finding expands the range of possible clinical signs that veterinarians may need to consider.
However, swollen or inflamed eyelids can have many causes, including allergies, infections and other inflammatory conditions. The presence of blepharitis alone is therefore not evidence that a dog has toxoplasmosis.
The researchers also noted that several dogs had other medical problems, including immune-related diseases and visceral leishmaniasis. Some had histories of treatment that could suppress immune function. These circumstances may have influenced how the infections developed, although five cases are insufficient to establish reliable risk factors.
Treatment Helped, but Relapses Occurred
All five dogs initially improved after receiving systemic clindamycin, an antibiotic used to treat toxoplasmosis, together with medication to control inflammation in the eyes.
Unfortunately, the improvement was not always permanent. Two dogs subsequently developed recurring ocular inflammation despite prolonged treatment. Their antibody levels also remained elevated, suggesting that managing suspected ocular toxoplasmosis can be difficult in some patients.
These findings raise questions about how long affected dogs should be monitored and whether additional treatment approaches may be necessary when the disease returns.
The researchers caution that diagnosing ocular toxoplasmosis remains challenging. A positive antibody test indicates exposure to the parasite but does not automatically prove that it caused a dog’s eye disease. Veterinarians must consider other possible explanations and interpret laboratory results alongside clinical findings.
The study was also retrospective, meaning the researchers examined existing medical records rather than conducting a controlled treatment trial. Consequently, the results cannot establish how effective clindamycin is for dogs with this condition.
What Dog Owners Should Know
For owners, the most important message is not that toxoplasmosis represents a newly discovered widespread threat. The research does not provide evidence that large numbers of dogs are developing eye disease from this parasite.
Instead, it highlights another possible explanation for serious or persistent eye inflammation, particularly in dogs with other illnesses or weakened immune systems.
Warning signs that deserve prompt veterinary attention include pronounced eye redness, visible discomfort, squinting, unusual sensitivity to light and sudden changes in vision. Such symptoms can have numerous causes, some of which require urgent treatment to prevent permanent damage.
Owners should not attempt to diagnose toxoplasmosis themselves or administer antibiotics without veterinary guidance. A thorough eye examination and appropriate laboratory testing are essential.
More Research Is Needed
The Israeli study provides valuable clinical observations, but its small size is an important limitation. Five cases cannot establish how common ocular toxoplasmosis is in dogs or determine which animals face the greatest risk.
Larger studies will be needed to improve diagnostic methods, investigate possible risk factors and identify effective treatment strategies for dogs experiencing repeated inflammation.
For now, the research offers an important reminder that familiar infectious organisms can sometimes produce unexpected complications. Recognising those possibilities may help veterinarians protect the eyesight of dogs whose symptoms would otherwise remain unexplained.
Primary Sources
1. Original peer-reviewed scientific paper
Soueid, Y., Ofri, R., Sebbag, L., Aroch, I., and Pe’er, O. (2026).
More than a feline disease: Ocular manifestations in five dogs infected with Toxoplasma gondii.
Veterinary Parasitology: Regional Studies and Reports, Volume 75, Article 101590.
Published: October 2026.
DOI: 10.1016/j.vprsr.2026.101590.
2. Official university research record
Hebrew University of Jerusalem — verified publication record
The university’s research database confirms the authors, peer-reviewed publication, study design, findings and conclusions. It also identifies the paper as open access under a Creative Commons Attribution licence.
3. Research announcement — 9 November 2026
