Symptoms and signs of feline infectious peritonitis (FIP)

Overview of FIP Manifestations

Feline Infectious Peritonitis (FIP) is a complex and often fatal viral disease caused by mutated feline coronavirus (FCoV). It predominantly affects young cats, although older felines are not entirely exempt. The disease manifests in two primary forms: the effusive (wet) form and the noneffusive (dry) form. Recognizing the clinical signs associated with each type is essential for early diagnosis and intervention.

Effusive (Wet) Form: Symptoms and Indicators

The hallmark of the wet form is the accumulation of fluid within body cavities such as the abdomen and chest, leading to noticeable swelling and respiratory distress. Clinical signs generally develop rapidly and include:

Ascites: Abdominal distension due to fluid buildup, often causing a visibly swollen belly.

Dyspnea: Labored breathing resulting from pleural effusion, signified by rapid, shallow breaths.

Pleural effusion: Accumulation of straw-colored or serous fluid in the thoracic cavity, leading to respiratory compromise.

Weight loss: Rapid and unintentional, often accompanied by a decrease in muscle mass.

Fever: Persistent, often fluctuating, indicating an ongoing inflammatory response.

Lethargy: Reduced activity levels, depression, and decreased interaction with owners.

Anorexia: Loss of appetite, contributing to further weight decline.

Noneffusive (Dry) Form: Symptoms and Clinical Signs

The dry form is characterized by granulomatous inflammation without significant fluid buildup. Its presentation is more insidious, often complicating early diagnosis. Characteristics include:

Neurological signs: Ataxia, seizures, or behavioral changes as immune complexes infiltrate the nervous system.

Ocular abnormalities: Anterior uveitis, chorioretinitis, or other ocular lesions leading to cloudy corneas or blindness.

Weight loss and lethargy: Similar to the wet form but tend to progress more gradually.

Fever: Recurrent or persistent, often unresponsive to antibiotics.

Gingivitis or oral ulcers: Less common but reported in some cases.

Lymphadenopathy: Swollen lymph nodes, indicating immune response.

Additional Indicators and Subtle Signs

Certain subtle signs can point toward FIP in both forms, especially in early stages:

Vague abdominal discomfort: Mild discomfort or reluctance to jump or climb.

Poor coat condition: Dull, unkempt fur, and poor grooming habits.

Dehydration: Due to fluid shifts and reduced intake, often detected by skin tenting.

Behavioral changes: Reduced activity, hiding, or reluctance to move.

Laboratory and Diagnostic Clues

While clinical signs are key, laboratory findings provide valuable support:

Anemia: Usually non-regenerative, indicating chronic disease.

Hyperproteinemia: Elevated proteins in blood serum, especially globulins.

Elevated total protein levels: Due to increased globulins from immune response.

Hydrolytic fluid analysis: In wet FIP, fluid analysis shows high protein concentration, low cellularity, and specific characteristics like viscosity.

Polymerase chain reaction (PCR): Detects FCoV RNA, aiding in confirming diagnosis.

Immunohistochemistry: Detects FCoV antigens in tissues or fluids, considered a definitive diagnostic modality.

Progression of the Disease

The rapid progression of FIP often results in rapid deterioration once clinical signs appear. The wet form tends to be more acute, with rapid fluid accumulation and respiratory compromise, while the dry form can extend over weeks, with organ-specific signs predominate.

Variability and Overlap in Signs

Due to the diverse organs involved, symptoms often overlap with other feline diseases. For example, neurological signs may resemble toxoplasmosis, and ocular signs can mimic other uveitic conditions. This variability underscores the importance of comprehensive diagnostic approaches.

Uncommon but Noteworthy Signs

In rare cases, cats may present with:

Cutaneous lesions: Ulcers or nodules under the skin.

Gastrointestinal signs: Vomiting, diarrhea, or abdominal pain unrelated to other causes.

Muscular atrophy: Due to cachexia or neurological impairment.

Conclusion

Early recognition of FIP hinges on understanding its broad spectrum of signs. The effusive and noneffusive forms, while distinct, share some overlapping clinical features, complicating diagnosis. Advances in diagnostic tools continue to improve detection, yet clinical suspicion remains paramount, especially in young cats exhibiting persistent fever, weight loss, and organ-specific abnormalities. Moving beyond conventional diagnostics, emerging research into immune response modulation offers hope for future therapeutic strategies against this elusive disease.