What Are the Types of Feline Infectious Peritonitis?

There are two main forms of FIP in cats: wet (effusive) and dry (non-effusive). Each type behaves differently, but both are caused by the same mutated virus.

Wet Feline Infectious Peritonitis

Wet FIP is the more recognizable form of the disease. It rapidly progresses, with fluid accumulating in the body cavities. This buildup of fluid will lead to noticeable physical changes, which in turn can affect the heart, lungs, and other organs.

The common signs of FIP in cats include: 

• Abdominal Swelling. A swollen belly is a common sign of wet FIP in cats. It’s caused by the accumulation of a yellowish and thick fluid. While this isn’t usually painful, it may apply pressure on nearby organs. 

• Breathing Difficulties. If the fluid accumulates in the chest cavity rather than the abdomen, it can put pressure on the lungs, making it difficult for the cat to breathe. This leads to labored or open-mouth breathing, indicating the need for emergency care. 

• Weight Loss and Poor Coat. Cats affected by wet FIP may lose a significant portion of their weight and have a much poorer coat quality. The cat will feel very thin along the spine, even with the swollen belly. 

• Lethargy and Anorexia. Extreme lethargy and a poor appetite are possible symptoms of wet FIP. 

Dry Feline Infectious Peritonitis

Dry FIP is more subtle and slower than its wet counterpart. Instead of fluid buildup, it leads to granuloma formation. Granulomas are masses of inflammatory cells, which can lead to organ damage.

Common signs of dry FIP in cats include:

• Neurological Symptoms. When FIP affects the brain and spinal cord, affected cats may experience ataxia, loss of coordination, trembling, tremors, seizures, or even paralysis. 

• Ocular Symptoms. Dry FIP can cause uveitis, cloudy eyes, uneven pupil sizes, bleeding in the front part of the eye, retinitis, and even vision loss. 

• Organ Inflammation. The granulomas affect internal organs such as the liver, kidneys, and intestines. This leads to vomiting, abdominal pain, or jaundice. 

• Fever and Lethargy. Like the wet form, cats with dry FIP may have increased body temperature and persistent lethargy. 

• Loss of Appetite. Some cats may lose their appetites, refusing to eat even their favorite meals.

Mixed FIP

In some cases, feline infectious peritonitis can be mixed, meaning cats can experience both signs of wet and dry forms. For example, a cat may develop dry FIP and later develop the associated symptoms of wet FIP. However, the mixed form is quite uncommon.

How Do Vets Diagnose FIP in Cats?

We do a multimodal approach, where we combine history, clinical signs, examinations, and laboratory tests.

Bloodwork 

Blood tests help us identify factors that may point to FIP. This includes high globulin proteins, an albumin-to-globulin ratio of less than 0.4, and decreased lymphocytes. 

Effusion Analysis

If fluid is present, a sample will be taken and analyzed. We’ll do a Rivalta’s test, which is where a drop of fluid is added to a distilled water and acetic acid mixture. If the drop holds its shape, then the possibility that the cat has FIP is high. 

Another method is to check for high protein content and low cell counts. 

Imaging

We may use X-rays and ultrasounds to detect fluid buildup in the chest or abdomen of cats suspected of the wet form. Our team will also check for enlarged lymph nodes and organ abnormalities, which may indicate dry FIP.

PCR Test

A polymerase chain reaction test can detect the feline coronavirus in fluid or tissue. It works by replicating the genetic material, allowing it to be identified. However, the test cannot distinguish between the harmless and the mutated strain. 

Biopsy

The gold standard for diagnosing FIP in cats is a biopsy. This method allows us to directly examine the affected tissue for the presence of the virus. We can also use a special staining technique, known as immunohistochemistry, to detect the FIP virus antigen directly. 

How Do You Treat FIP in Cats?

Treatment will focus on medication and supportive care. 

Medication

Feline infectious peritonitis in cats was initially considered untreatable, but major breakthroughs and advancements have been effective. This included treatment options such as GS-441524 and remdesivir. If GS-441524 fails, molnupiravir can be given as an alternative. 

Supportive Care

For cats with no access to these antiviral treatments or those in the advanced stages of the disease, supportive care will be the option. These methods aim to improve the cat's life and comfort. 

If your cat’s abdomen has become bloated to the point that certain movements are challenging, we will drain the fluids. Draining reduces the pressure, improving breathing. Additionally, supportive medications can help manage symptoms and alleviate the discomfort. 

“A cat’s health is the product of several years of research, cooperation, and love.”

- Dr. Lidija Krvavac

Final Thoughts

While feline infectious peritonitis is still a challenging diagnosis, the veterinary community’s growing understanding of the disease offers hope for improved treatments and outcomes. The continued research for more possible treatments helps give affected cats a chance at a smooth recovery.