In the “dry” form of feline infectious peritonitis (FIP), ocular symptoms occur relatively frequently and may be among the first signs that draw the attention of the veterinarian. These manifestations are the result of inflammation in the ocular structures and can vary in intensity and location. Among the most common are:

Anterior uveitis – the eye may appear red, with a "hazy" appearance, and the cat may exhibit sensitivity to light (photophobia).

Changes in iris color – sometimes the iris acquires an uneven shade or discolored spots appear.

Deposits on the cornea or in the anterior chamber – Visible inflammatory precipitates may appear in the form of whitish spots.

Ocular hemorrhages – small bleeding inside the eye, which can affect vision.

Progressive vision loss – untreated inflammation can lead, over time, to serious impairment of visual function, sometimes even blindness.

These ocular signs, along with persistent fever, weight loss, and other systemic manifestations, support the suspicion of FIP, but they can also be found in other diseases, making diagnosis even more difficult.

In feline infectious peritonitis (FIP), persistent fever is one of the most important and difficult to control clinical signs. It has several characteristics that make it suggestive of this disease:

The oscillating, but ever-present character – the cat may have periods when the temperature drops slightly, but rarely returns completely to normal. The fever remains constant, even when the animal receives regular treatment with antibiotics or anti-inflammatories.

Resistance to conventional treatments – this type of fever does not respond to usual therapies for bacterial infections, which raises suspicion of a viral and immune cause, such as FIP.

The mechanism of fever – In FIP, fever occurs due to an exaggerated reaction of the immune system to the mutated feline coronavirus. The virus triggers chronic inflammation, with the release of cytokines and other pro-inflammatory substances that disrupt thermoregulation. Basically, the body constantly “perceives” a threat and maintains a high temperature.

This persistent fever, associated with lethargy, loss of appetite and progressive weight loss, is an essential element in the clinical picture of PIF and one of the reasons why the veterinarian considers this disease when other more common causes of fever have been excluded.

Lethargy is a common symptom in cats affected by feline infectious peritonitis (FIP) and is characterized by marked fatigue, lack of energy, and decreased interest in daily activities. Basically, the cat sleeps more than usual, moves less, avoids play and interaction, and sometimes even eats less.

The causes of this state of lethargy in PIF are multiple:

The effect of persistent fever – a high and constant body temperature exhausts the body, causing weakness and lack of vitality.

Chronic inflammation – the exaggerated immune response against the mutated feline coronavirus consumes a lot of energy, which makes the cat seem constantly tired.

Malnutrition and weight loss – due to reduced appetite and increased consumption of resources by the inflammatory process, the body enters an energy imbalance, accentuating the feeling of weakness.

Damage to internal organs – depending on the form of the disease, accumulated fluid (in the "wet" form) or granulomatous lesions (in the "dry" form) can affect the liver, kidneys or nervous system, contributing to a general state of apathy and lack of reactivity.

Weight loss is a characteristic and very common symptom in cats with feline infectious peritonitis (FIP), regardless of the form of the disease ("wet" or "dry"). It reflects the generalized impact of the infection and the exaggerated immune response on the metabolism and health of the animal.

Why does weight loss occur in PIF?

Reduced appetite (anorexia or hyporexia)
Affected cats eat less due to persistent fever, abdominal discomfort, or general malaise.
Over time, insufficient caloric intake leads to loss of body mass.

Increased energy consumption of the body
The chronic inflammatory process and the immune system's fight against the virus consume a lot of energy resources.
The body begins to use fat and muscle reserves to cope with this constant "alert state".

Malabsorption and damage to internal organs
In FIP, the liver, kidneys, and digestive system may be affected by granulomatous lesions or accumulated fluid.
These changes reduce the body's ability to digest and use nutrients efficiently.

Muscle wasting (cachexia)
The cat loses not only fat, but also muscle mass, which is noticeable through body weakness, prominent ribs, and decreased physical strength.

How is it observed clinically?

• The silhouette becomes visibly slimmer, even if the abdomen may be enlarged in volume (in the "wet" form).
• The cat appears fragile, with reduced muscle mass, dull fur, and less mobility.
• Weight loss progressively increases, in parallel with the worsening of other symptoms (lethargy, fever, digestive or neurological disorders).

Basically, weight loss in FIP is the combined result of reduced food intake, increased energy consumption, and damage to internal organs, being an important sign of the severity of the disease.

The effect of persistent fever

• High and constant temperatures disrupt normal appetite mechanisms.
• The cat feels a general state of discomfort and loses interest in food.

Systemic inflammatory process

• The virus and the exaggerated immune response release substances (cytokines) that act on the hunger nerve centers in the brain, inhibiting them.
• Basically, the body "behaves" as if it were chronically ill and voluntarily reduces food intake.

Abdominal discomfort and effusions (in the “wet” form)

• The fluid accumulated in the abdomen causes a feeling of pressure, nausea, and lack of interest in food.

Damage to internal organs (in "dry" form)

• Granulomatous lesions in the liver, kidneys, or intestines lead to digestive and metabolic disorders.
• The cat may experience nausea, vomiting or diarrhea, increasing its loss of appetite.

Neurological impact (in some cases)

• If the disease affects the central nervous system, eating behavior disorders or motor difficulties may occur that prevent the cat from eating normally.

How does it manifest clinically?

• The cat eats less and less or completely refuses food, including favorite foods.
• Sometimes they only consume water, sometimes even that is reduced.
• The loss of appetite becomes persistent and progressive, not going away with a change in food or regular treatments.
• It is often accompanied by lethargy, weight loss, and dull fur.

Loss of appetite in FIP is, therefore, the consequence of a set of factors - fever, chronic inflammation, visceral damage and general discomfort - and represents an alarm sign for the veterinarian, especially when it persists despite usual therapies.

Accumulation of fluid in the chest cavity (hydrothorax)

• In the "wet" form, pleural effusion is a major cause of dyspnea.
• Fluid accumulates between the lungs and the chest wall, reducing the space needed for the lungs to expand during inspiration.
• The cat breathes heavily, with large and rapid movements, and sometimes breathing with the mouth open is observed.

Diaphragmatic pressure due to abdominal fluid

• In the case of ascites, the enlarged abdomen pushes the diaphragm upward, further limiting lung expansion.
• This combined pressure accentuates the sensation of "lack of air".

Inflammation of lung tissue

• In the "dry" form, granulomatous lesions may appear in the lungs, which reduce the surface area available for gas exchange.
• This leads to hypoxia (decreased oxygen in the blood) and chronic respiratory difficulties.

Nervous system damage

• If the disease affects the central nervous system, including the respiratory control centers, respiratory rhythm disorders or ineffective breathing may occur.

How does it manifest clinically?

• Rapid and shallow breathing.
• Visible effort when inhaling, the cat sometimes standing with its neck stretched out and its elbows away from the body.
• Abnormal breath sounds.
• Cyanosis of the mucous membranes in severe cases, due to lack of oxygen.
• Increased lethargy, as the cat avoids movements that would increase its oxygen consumption.

In conclusion, respiratory distress in PIF most often occurs due to fluid accumulation in the chest and/or abdomen, but also due to inflammatory lung lesions or neurological damage. This symptom is an indicator of severity and, when it occurs, requires rapid intervention to stabilize the cat.