Wet FIP vs Dry FIP: The 2026 Definitive Comparison Guide
- DVM Vien
- May 12
- 3 min read
Quick answer: Wet FIP causes fluid buildup in the abdomen or chest within days and progresses fast. Dry FIP affects organs gradually with subtle symptoms — fever, weight loss, eye changes. Both forms respond to GS-441524 at 6–10 mg/kg/day for 84 days, but dry FIP needs higher starting doses (typically 8 mg/kg) and longer to show visible improvement. About 60% of FIP cases are wet, 40% dry.
What is wet FIP?
Wet FIP — also called effusive FIP — is the form where the body's immune response causes blood vessels to leak protein-rich fluid into the abdomen (ascites) or chest (pleural effusion). Cats develop visibly swollen bellies within days, often with laboured breathing if fluid reaches the chest.
Wet FIP symptoms in order of appearance
Persistent fever (39.5–41°C) unresponsive to antibiotics — often the first sign
Lethargy and reduced appetite for 3–7 days
Visibly distended abdomen from fluid accumulation
Difficulty breathing if fluid reaches the chest cavity
Rapid weight loss despite the swollen belly
Jaundice in late-stage cases
What is dry FIP?
Dry FIP — also called non-effusive FIP — is the slower, sneakier form. Instead of fluid leakage, the immune response causes inflammatory lesions (granulomas) to form in solid organs: kidneys, liver, spleen, lymph nodes, eyes, and central nervous system. Many cats are treated for 'fever of unknown origin' for weeks before FIP is suspected.
Dry FIP symptoms by organ affected
Eyes (ocular FIP): uveitis, cloudiness, colour changes, uneven pupils
Brain (neurological FIP): behavioural changes, seizures, head tilt, wobbly gait
Kidneys: increased thirst and urination, weight loss
Liver: jaundice, elevated liver enzymes on bloodwork
Lymph nodes: palpable enlargement under the jaw or in the abdomen
How do vets diagnose each form?
Diagnosis combines clinical exam, bloodwork, and imaging. Wet FIP is usually confirmed by ultrasound showing free fluid plus a high-protein, low-cellularity fluid sample (Rivalta test positive). Dry FIP is identified through bloodwork showing high globulins, low albumin, A:G ratio under 0.4, elevated AGP, and lymphopenia. Imaging may show enlarged lymph nodes or organ lesions. Both forms can be confirmed by PCR testing detecting feline coronavirus RNA in tissue, fluid, or blood.
For more on early symptom recognition, see our stage-by-stage symptom guide.
How does treatment differ between wet and dry FIP?
Both forms are treated with GS-441524 for 84 days, but the starting dose differs by FIP form. Wet FIP starts at 6 mg/kg/day. Dry FIP starts at 8 mg/kg/day. Ocular and neurological forms start at 10 mg/kg/day regardless of whether they present as wet or dry. The drug is the same — only the dose and the time-to-visible-improvement change. Wet FIP cats often look dramatically better within a week. Dry FIP cats can take 2–4 weeks before owners see real change.
Can a cat have both wet and dry FIP?
Yes. Mixed FIP — where a cat has both fluid accumulation and organ-specific lesions — is increasingly recognised, especially in late-stage cases. Roughly 10–15% of FIP cases show features of both forms. Treatment is the same: GS-441524 for 84 days, dosed for the more severe component (usually the dry/organ involvement).
Survival rates with GS-441524 treatment
Before GS-441524, FIP was effectively a death sentence — over 95% of cats died within weeks. The 2019 Pedersen study at UC Davis changed that. Wet FIP on the 84-day protocol shows about 85% remission. Dry FIP shows about 80%. Neurological FIP at 10 mg/kg shows about 70%. Untreated FIP of any form shows under 5% spontaneous remission. Individual outcomes depend on early treatment, dose consistency, and completing all 84 days.
Frequently Asked Questions
Is wet FIP or dry FIP more dangerous?
Wet FIP progresses faster and kills sooner without treatment — typically within weeks. Dry FIP progresses slower but can cause permanent organ damage by the time it's diagnosed, especially if the brain is affected. With prompt GS-441524 treatment, survival rates are similar (80–85%).
Can wet FIP turn into dry FIP?
Yes. The two forms exist on a spectrum. As treatment progresses and fluid resolves, what looked like pure wet FIP may reveal underlying dry-form organ involvement. This is why the full 84-day course matters — don't stop because the fluid is gone.
How fast does wet FIP progress without treatment?
From first symptoms to death is typically 2–8 weeks for untreated wet FIP. The fluid accumulation can become life-threatening within days if it reaches the chest cavity and impairs breathing.
Do wet and dry FIP cost different amounts to treat?
Yes. Dry, ocular, and neurological forms need higher doses (8–10 mg/kg vs 6 mg/kg), which means more vials per 84-day course. See our full FIP treatment cost breakdown for worked examples.
This article is informational and does not constitute veterinary advice. Statistics from Pedersen et al. (2019).
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