Encephalitozoonosis in Cats: A Vet’s 2025 Guide to Recognition, Treatment & Ocular Care 🐱🧠

Hello, I’m Dr. Duncan Houston BVSc, veterinarian and founder of Ask A Vet. In this in-depth 2025 guide, we explore Encephalitozoon cuniculi infection—aka encephalitozoonosis—in cats. Though once considered rare, this protozoal parasite is now known to cause significant eye disease and systemic signs in some cats. Here’s how to spot red flags, pursue reliable diagnostics, treat with fenbendazole, and support your cat through an effective home‑care plan—especially for ocular concerns.

📘 What Is Encephalitozoonosis?

Encephalitozoon cuniculi is a microsporidian pathogen—technically a parasite‐fungus—that infects various mammals, including cats and rabbits :contentReference[oaicite:3]{index=3}. Though cats often act as asymptomatic carriers, they may develop eye inflammation, cataracts, and vision issues when clinical disease occurs :contentReference[oaicite:4]{index=4}.

👀 Why It Matters in 2025

• Increasing reports of ocular involvement in cats—including uveitis and cataracts :contentReference[oaicite:5]{index=5}.
• Often misdiagnosed or overlooked due to non-specific signs.
• Prompt recognition prevents vision loss through targeted treatment.

🚨 Clinical Signs to Watch For

Encephalitozoonosis in cats primarily causes eye changes, occasionally accompanied by systemic signs:

• Anterior uveitis: red eyes, pain, squinting, photophobia :contentReference[oaicite:6]{index=6}.
• Cataracts: focal cortical lens opacities in young to adult cats :contentReference[oaicite:7]{index=7}.
• Glaucoma: increased intraocular pressure as a complication.
• Systemic signs: rare kidney, brain, or lung involvement :contentReference[oaicite:8]{index=8}.

🧭 Diagnostic Approach

1. History & Physical Exam: note outdoor/rabbit exposure, eye changes.
2. Ocular examination: slit-lamp check, intraocular pressure.
3. Serology (IFAT): suitable screening test—not definitive but useful :contentReference[oaicite:9]{index=9}.
4. PCR testing: on aqueous fluid or lens matter for confirmation :contentReference[oaicite:10]{index=10}.
5. Ocular imaging or biopsy: histopathology confirms spores (Gram‑positive) :contentReference[oaicite:11]{index=11}.
6. Systemic screening: evaluate kidneys or CNS if signs present.

💊 Treatment With Fenbendazole

• Fenbendazole – 20 mg/kg orally once daily for 3 weeks is effective :contentReference[oaicite:12]{index=12}.
• Ocular support: topical anti-inflammatory drops where needed.
• Phacoemulsification: cataract surgery for lens removal to preserve vision :contentReference[oaicite:13]{index=13}.
• Corticosteroids: low-dose systemic use, balancing immunosuppression risk.

📈 Prognosis & Follow‑Up

• Early treatment leads to resolution of uveitis and partial vision preservation :contentReference[oaicite:14]{index=14}.
• Cataract formation may require surgery; untreated cases risk irreversible vision loss.
• Some cats may need long‑term monitoring; repeat serology, eye checks, and pressure tests.

🏡 Home Care Essentials

• Administer fenbendazole and ocular meds with reminders via Ask A Vet app.
• Provide a calm, dim environment to reduce eye pain.
• Track appetite, vision, tearing, and behavior changes.
• Ensure regular veterinary rechecks—at least every 4 weeks during treatment.

📚 Case Example

“Milo,” a 3‑year‑old indoor/outdoor cat, developed sudden red eye and pain. IFAT was positive; PCR from aqueous detected spores. He received 3 weeks of fenbendazole and topical steroids. Uveitis resolved within 10 days and vision remained normal at 6‑month follow‑up.

🚨 When to Seek Emergency Help

• Severe eye pain, cloudiness, or sudden vision loss.
• Persistent uveitis despite treatment.
• Neurological signs—head tilt or ataxia may suggest CNS involvement.

✨ Final Thoughts

Encephalitozoonosis in cats is emerging as a significant cause of ocular disease. With enhanced recognition and targeted therapy, many cats can preserve vision and comfort. Using Ask A Vet tools—medication reminders, symptom trackers, and teleconsults—you can confidently guide your cat through effective treatment and recovery 🐾❤️.

For personalized plans, follow-up reminders, and expert advice, visit AskAVet.com or download the Ask A Vet app.