Feline infectious peritonitis (FIP) is a common and deadly disease for cats. Not only that, but it also more than one variant and can affect a cat in different ways. In this article, we will talk about the different types of FIP that can be manifested.

Types Of Cat FIP

FIP can manifest in three different ways: a wet, effusive, exudative form; a dry, granulomatous, parenchymatous, noneffusive form; and a mixed form. A fibrinous peritonitis, pleuritis, or pericarditis with effusions in the abdomen, thorax, and/or pericardium, respectively, are characteristics of the first kind. The CNS and other organs, including the eyes, exhibit granulomatous alterations in the second variant, which lacks evident effusions. Since each cat with FIP exhibits effusion to varying degrees together with more or less granulomatous organ alterations, it has been established that differentiating between these kinds is not helpful (and only beneficial for the diagnostic method). The forms can also change into one another. Thus, FIP can simply be more or less productive or exudative in a particular cat at a specific moment.

Differences between dry and wet FIP

Non-effusive “dry” FIP

There is little to no fluid buildup in “dry” or non-effusive FIP in some felines. In the dry form, the eyes, brain, liver, intestine, or other body organs are frequently severely inflamed, which can cause a number of clinical symptoms. For many cats with non-effusive FIP, eye problems are the only clinical symptom.

When a disease takes hold, the majority of those affected quickly deteriorate, but some cats can function normally for a few weeks. Sadly, almost every instance of the illness will result in death.

Only a small portion of cats exposed to feline coronavirus, even those that have the potential to cause FIP, are able to mount a defence against it, leading to clinical illness in most infected cats. However, as was already mentioned, those who do become ill almost invariably pass away.

Effusive “wet” FIP

The collection of fluid in the chest or belly, which can make breathing difficult, is the defining clinical symptom of effusive FIP. Lack of appetite, fever, weight loss, jaundice, and diarrhoea are further symptoms.

DIAGNOSIS OF WET & DRY FIP

Diagnosing effusive FIP

The effusive type of the disease is now easier to diagnose than it once was. Effusive FIP can be diagnosed if viral RNA is found in a sample of the effusion (liquid drained from the body), for example, using a reverse transcription polymerase chain reaction (RT-PCR). However, doing so necessitates sending a sample to an outside veterinary laboratory. Several diagnostics available at the veterinary hospital can quickly rule out an exuberant FIP diagnosis, including:

1. Check the effusion’s total protein content; if it is less than 35g/L, FIP is incredibly unlikely.
2. Determine the albumin to globulin ratio in the effusion; if it is greater than 0.8, FIP is ruled out; if it is less than 0.4, FIP is a potentially diagnosable but uncertain condition.
3. Inspect the cells in the effusion; if the majority of them are lymphocytes (a type of white blood cell), FIP is ruled out as a diagnosis.

Diagnosing non-effusive FIP

Because the clinical indications of non-effusive FIP tend to be more ambiguous and variable than those of effusive FIP, the list of differential diagnoses is substantially longer. When the following conditions are met, non-effusive FIP diagnosis should be taken into consideration.:

1. Background: The cat is young (under 2 years old) and purebred; pedigree kittens account for nearly 70% of FIP cases.
2. Prior events: the cat was under stress because of a recent neutering or vaccination
3. Past: The cat may have had a chance to get FCoV due to factors including having come from a breeding or rescue cattery or having recently been introduced to a purebred kitten or cat.
4. Clinical indicators include intra-ocular signs, anorexia, eating less than usual, failing to put on weight, failing to gain weight, becoming anorexic, and jaundice.
5. Hypergammaglobulinemia; elevated bilirubin without elevated liver enzymes.
6. Lymphopenia with non-regenerative, typically moderate, anaemia.
7. Serology: Due to the high incidence of FCoV in breeding and rescue catteries, this parameter should be used with caution. The cat exhibits a high antibody titre to FCoV.

If the cat is seronegative, non-effusive FIP can be ruled out as a diagnosis if the antibody test has great sensitivity. The FCoV Immunocomb (Biogal), the Speed F-Corona rapid immunochromatographic (RIM) test (Virbac), and the fastest feline infectious peritonitis (MegaCor Diagnostic) RIM test were all shown to be 100% sensitive in a study that examined multiple commercially available in-house FCoV antibody tests.

With two different major types of FIP, cat owners should be more knowledgeable on this topic, so they know how to better treat their cats in the worst-case scenario. If they don’t properly educate themselves on different types of FIP, they may consult to their veterinarian to find a proper way to treat their cat’s FIP.

Ocular FIP

This type of FIP can cause severe complications in cats, as it also penetrates through the blood eye barrier.

 

Blood eye barrier

The blood eye barrier in cats is an important protective barrier against the spread of FIP. This barrier is composed of cells that line the anterior chamber of the eye, and these cells act to prevent pathogens from entering and causing inflammation in this sensitive area.

While this makes it difficult for a virus such as FCoV to access ocular structures, lesions can happen due to the breakdown of barriers when chronic inflammation occurs.

Protease inhibitors like GC376 have also been shown not to be effective at crossing the blood-to-eye barrier which makes them less useful in treating cases where ocular structures may be affected by FIP.

For macrophages loaded with virus particles to enter ocular structures they need to first breach this layer; without successful passages through each successive layer, disease transmission cannot occur.

 

How Dry FIP develop into Ocular FIP

Dry FIP is the more deadly form of the disease and can potentially progress into Ocular FIP in about one-third of cats suffering from this type. In Ocular FIP, or uveitis, eye lesions develop as the result of the weakening of the blood-eye barrier due to the virus. This leads to increased glucose levels which causes swelling and inflammation in the eyes.

 

Neurological FIP

Dry FIP can also develop into the most dangerous form of FIP, Neurological FIP.

 

The blood brain barrier

A blood brain barrier (BBB) is an important protective layer formed by special cells that line the walls of the tiny vessels in and surrounding the brain. This extremely tight barrier plays an essential role in protecting our central nervous system from harm by blocking potentially toxic materials circulating through the bloodstream, including systemic toxins.

It’s therefore unsurprising that when this barrier is compromised due to various conditions or infectious agents, neurological disruptions may be witnessed like what can occur as a result of FIP.

FIPV, which causes an intense inflammatory reaction around vessels in various tissues, including the brain, is a common cause responsible for 45-50% of all cases related to infection-induced neurologic diseases in cats.

It other words, losing this important shield can greatly increase their risk of developing neurological complications arising from FIPV infection and would have serious implications on therapeutic interventions.

 

How Dry FIP develop into Neurological FIP

Dry FIP can progress to the next stage of neurological FIP in some cases. The density and proliferation of circulating white blood cells and monocytes increase as Dry FIP progresses. These cells persistently enter the cerebrospinal fluid until an inflammatory state is generated, resulting in neurological damage.

Neurological FIP affects primarily a cat’s nervous system, with most common symptoms such as tremors, walking difficulty (ataxia), mental confusion and aggressive behavior.