Understanding Feline Infectious Peritonitis: Wet vs. Dry Forms

Feline Infectious Peritonitis (FIP) is a severe, often fatal disease resulting from the replication of a mutated feline enteric coronavirus within the host's monocytes and macrophages. Unlike Feline Asthma, which primarily affects the airways, FIP is a systemic condition. The clinical expression is broadly divided into two presentations: Effusive (wet) and Non-effusive (dry). The wet form causes severe inflammation of the blood vessels, leading to protein-rich fluid leakage into body cavities. The dry form is characterized by the development of pyogranulomas in parenchymal organs.

Effusive FIP Pathology

In the wet form, the body's immune system mistakenly attacks the virus-infected cells, causing massive leakage of plasma into the abdominal or pleural space. This can mimic symptoms seen in Chylothorax (Feline), where fluid buildup leads to respiratory distress.

Non-effusive FIP Pathology

Dry FIP involves the formation of localized granulomas. These lesions can manifest in the eyes, kidneys, or the central nervous system. When the eyes are affected, symptoms may mirror those of Eosinophilic Conjunctivitis, leading to ocular pain and secondary visual impairment. If the infection reaches the central nervous system, owners may observe seizures or behavioral changes, which are distinct from the bladder-focused distress seen in Feline Idiopathic Cystitis.

Recognizing Clinical Warning Signs

Early recognition of symptoms is the most important factor in patient management. While Megacolon presents with straining to defecate, FIP often presents with generalized weakness and recurring, non-responsive fevers.

Physical Manifestations

  • Persistent, high-grade fever

  • Distended abdomen due to fluid accumulation

  • Rapid weight loss and muscle atrophy

  • Ocular inflammation (uveitis or keratitis)

  • Neurological abnormalities (ataxia or tremors)

When to Seek Emergency Care

If your cat exhibits acute labored breathing, extreme lethargy, or sudden collapse, these are emergency indicators. Similar to the acute crisis seen in Toxicity (Lily), FIP-related complications can decline rapidly. An Feline Ocular Sarcoma diagnosis is sometimes considered during the differential process when uveitis is the primary symptom.

Etiology and Genetic Factors

FIP is not inherently 'contagious' in the way a cold virus is, as it arises from a mutation *within

  • the individual cat. However, the initial coronavirus is shed in feces and is highly contagious among cats in multi-cat households. The primary risk factor is the internal mutation of the virus within the host. Kittens and young cats under two years of age are statistically at the highest risk, as are cats in high-density environments like shelters or catteries.

Diagnostic Protocols

Veterinarians utilize a combination of blood panels, fluid analysis, and PCR testing to confirm the diagnosis. A complete blood count (CBC) often shows non-regenerative anemia and lymphopenia. If fluid is present, an analysis of the effusate (Rivalta test) is performed. While a Mediastinal Mass might be ruled out via imaging, FIP often presents with lymph node enlargement or specific renal changes.

Management Strategies

Treatment for FIP has evolved dramatically. Modern antiviral therapies (such as GS-441524) have shown significant success in putting the condition into long-term remission. Supportive care includes fluid therapy, nutritional support, and immunomodulatory medications to manage secondary inflammation. Unlike Feline Bronchial Disease, which requires long-term steroid management, FIP treatment is targeted at halting viral replication.