Dry (non-effusive) FIP symptoms: the quiet form that's easy to miss

Short answer: dry (non-effusive) FIP causes inflammatory masses called granulomas in the organs rather than fluid, so there's no swollen belly to point to. The signs are quieter and easy to mistake for other illness: a persistent fever, steady weight loss, and lethargy, plus organ-specific clues — and the eyes and nervous system are involved more often in the dry form.

The wet form of FIP announces itself — a belly filling with fluid, breathing trouble. Dry FIP is the opposite: it hides. That's exactly why it's so often caught late, and why knowing its pattern matters.

The core signs

Almost every dry-FIP cat shows some combination of:

A fever that persists or keeps returning and doesn't respond to antibiotics — see could a fever be FIP?
Gradual weight loss, often despite reasonable eating early on.
Lethargy and a general fading — the cat is "not themselves."
Poor appetite as it progresses.

These are vague on their own. What sharpens them is the combination, in a young cat, that doesn't resolve.

Organ-specific clues

Because dry FIP forms granulomas in specific organs, the extra signs depend on where they land:

Liver → jaundice (yellow gums, eyes, skin).
Kidneys → masses a vet may feel or see on ultrasound; changes in drinking or bloodwork.
Intestines / lymph nodes → thickened loops or lumps in the belly, sometimes vomiting or diarrhoea.
Eyes → ocular FIP — a colour change or cloudiness, more common in the dry form.
Brain and spine → neurological FIP — wobbliness, seizures, behaviour change, also more common in dry disease.

The ocular and neurological overlap is important: in dry FIP, the eyes and nervous system are involved far more often than in the wet form, and both change how treatment is dosed.

Why it's missed — and why that matters

With no dramatic fluid to find, dry FIP looks like "a cat that's slowly unwell," and can be chased through other diagnoses first. Its slower pace can buy a little time, but late diagnosis still worsens outcomes. If a young cat has an unexplained, persistent fever with weight loss — especially with any eye or balance changes — dry FIP belongs on the list.

Diagnosis and the hopeful part

Dry FIP is harder to confirm than wet (no effusion to sample), so the diagnosis leans more on bloodwork patterns, imaging, and increasingly PCR/immunostaining of tissue. It's worth pushing for a clear answer — because once diagnosed, dry FIP responds to the same antiviral treatment that cures the wet form, with the caveat that ocular and neurological involvement needs higher doses.

Not sure whether your cat's vague signs add up? A vet on WhatsApp can help you think it through — details below.

Not veterinary advice. Persistent illness in a cat warrants a veterinarian who can examine them.

References

Pedersen N.C. An update on feline infectious peritonitis: diagnostics and therapeutics. The Veterinary Journal, 2014. Find on PubMed
Efficacy of GS-441524 for FIP: a systematic review (2018–2024). Read on PMC