Types of FIP: Wet vs. Dry FIP

Feline Infectious Peritonitis (FIP) is a serious disease that affects cats of all breeds, ages, and backgrounds, especially young cats and kittens in shelters or multi-cat households. FIP arises when the commonly found feline coronavirus (FCoV) mutates within a cat’s body, transforming from a mild virus into a life-threatening systemic disease.

Veterinary professionals and pet owners across Australia and New Zealand are becoming increasingly familiar with FIP as awareness and diagnostic capabilities improve. Yet one of the most important aspects of understanding FIP lies in recognising its two primary forms: wet FIP and dry FIP.

Though both types stem from the same viral mutation, they differ significantly in symptoms, diagnosis, and even treatment challenges. In this article, we’ll walk you through the differences between these types of FIP, how each manifests, and what that means for cat care across Oceania.

What Is Wet (Effusive) FIP?

Wet FIP, also known as effusive FIP, is the more acute and easily recognised form of the disease. It’s called "wet" because it leads to the accumulation of fluid in body cavities, most commonly the abdomen or chest. This fluid build-up is a result of widespread inflammation in blood vessels (vasculitis) caused by the mutated virus.

Key Clinical Features of Wet FIP:

• Abdominal distension due to fluid build-up (ascites)

• Laboured breathing if fluid collects in the chest (pleural effusion)

• Lethargy, fever, and loss of appetite

• Weight loss, despite a rounded belly

• Pale gums or signs of dehydration
  

These symptoms usually develop rapidly, often over days to weeks. In the past, a wet FIP diagnosis was considered a death sentence, but recent antiviral treatments such as GS-441524 have significantly improved outcomes when used early.

Diagnostic Clues for Wet FIP:

• Rivalta test: A quick test to evaluate whether abdominal or thoracic fluid is consistent with FIP.

• Yellow, sticky fluid with high protein levels and low cellularity is typical.

• Ultrasound can reveal fluid pockets and thickened abdominal tissues.

• Blood tests often show elevated globulins, a low albumin: globulin ratio, and mild anaemia.

Because fluid is easily sampled, wet FIP is easier to diagnose than the dry form. Veterinarians in urban clinics across Australia and New Zealand are now able to more quickly identify and respond to these cases.

What Is Dry (Non-Effusive) FIP?

Dry FIP, or non-effusive FIP, is the chronic and harder-to-diagnose form of the disease. Unlike the wet form, dry FIP does not involve fluid buildup. Instead, it causes the formation of granulomas—inflammatory lesions—within internal organs such as the liver, kidneys, lymph nodes, eyes, and brain.

This form of FIP can mimic many other chronic conditions, including toxoplasmosis, lymphoma, or even bacterial infections, making diagnosis more challenging, especially in regional or rural clinics in New Zealand or Australia, where advanced testing may be limited.

Key Clinical Features of Dry FIP:

• Persistent fever unresponsive to antibiotics

• Weight loss and poor appetite

• Enlarged lymph nodes or kidneys

• Ocular changes, including eye inflammation or color change

• Neurological symptoms, such as unsteady gait, tremors, or seizures

Dry FIP progresses more slowly than the wet form. It often affects older kittens or adult cats and may be first noticed as a vague illness before organ-specific symptoms arise.

Diagnostic Clues for Dry FIP:

• Bloodwork abnormalities, especially low A:G ratio (< 0.4)

• Imaging (ultrasound or CT scans) may reveal organ granulomas or enlarged lymph nodes

• PCR testing of tissue aspirates can sometimes detect the virus

• Ophthalmic exams may reveal retinal vessel changes or uveitis (eye inflammation)
  

In some cases, neurological or ocular signs are the only clear indicators. This is why veterinarians must maintain a high index of suspicion, especially in cats with prolonged, unexplained illness.

Mixed or Atypical Presentations

Some cats present with a combination of both forms. For instance, a cat might have abdominal fluid (wet FIP) along with eye lesions or neurological issues (dry FIP). These mixed cases can confuse diagnosis but are increasingly recognised in clinical settings.

Veterinary teams across Oceania are encouraged to consider FIP as a differential diagnosis when multiple organ systems are involved, especially in young or shelter cats.

Prognosis and Treatment: Does the Type Matter?

In the past, FIP was always fatal. Today, with access to GS-441524-based antivirals, both wet and dry FIP can be treated, and cats can recover fully.

However, the type of FIP may influence treatment complexity and duration:

• Wet FIP responds more quickly to antivirals because symptoms are often identified early.

• Dry FIP, especially with neurological involvement, may require longer treatment (84+ days) and careful dosing adjustments.
  

Prognosis is generally better the earlier the treatment begins. In Australia and New Zealand, Cure FIP Oceania helps provide treatment access, dosage guidance, and recovery support to ensure the best outcomes possible.

Supporting Your Cat: What to Watch For?

Whether your cat is recovering or you're monitoring for signs, these tips help:

• Track temperature and energy levels daily.

• Monitor for changes in appetite, coordination, or eye clarity.

• Watch for fluid build-up or abdominal swelling.

• Maintain low-stress environments, especially for multi-cat homes.
  

Veterinary follow-up is essential, and many clinics in Oceania are now familiar with FIP management protocols.

Final Thoughts: Understanding Saves Lives

FIP can no longer be considered a mysterious, untreatable disease. Thanks to growing global research, improved diagnostics, and access to life-saving antivirals, many cats with FIP now recover and thrive.

Understanding the differences between wet and dry FIP empowers pet owners to advocate for their cats and seek timely care. Whether you're a veterinarian in rural New Zealand, a cat rescue coordinator in Melbourne, or a pet parent in Sydney, awareness and action make all the difference.

At Cure FIP Oceania, we’re committed to helping cats survive and beat FIP. If you suspect FIP or want help with treatment, don’t hesitate to reach out to our expert support team.