Causes of FIP: The Feline Coronavirus Connection

Feline Infectious Peritonitis (FIP) is one of the most misunderstood and heartbreaking diseases affecting cats. Commonly seen in young cats and kittens, FIP is not caused by a new or exotic virus but by a common virus that many cats carry without showing symptoms — the feline coronavirus (FCoV). In most cases, FCoV causes only mild or no illness, but in rare instances, it mutates inside the cat’s body, leading to the development of FIP.

In this article, we’ll explore the causes of FIP in detail, focusing on the feline coronavirus connection, how the mutation happens, and the environmental and genetic factors that influence this transformation. This is crucial information for cat owners in Australia and New Zealand, where FIP has been increasingly recognised in both rescue populations and household pets.

What is Feline Coronavirus (FCoV)?

Feline coronavirus (FCoV) is a common and generally benign virus that spreads via the faecal-oral route, often through shared litter boxes, grooming, or contaminated environments. It’s estimated that up to 90% of cats in multi-cat environments, such as shelters or catteries, have been exposed to FCoV at some point.

Importantly, FCoV typically causes either no symptoms or mild digestive upset. In its common form, it is referred to as feline enteric coronavirus (FECV), which is not dangerous in itself. However, the trouble begins when this virus mutates.

The Mutation: From Feline Coronavirus to FIP

The exact reason why FCoV mutates into the dangerous form that causes FIP is not yet fully understood. However, research suggests that the mutation occurs within the infected cat, rather than being passed between cats. This means that FIP is not contagious in the traditional sense — you cannot “catch” FIP from another cat, though you can catch FCoV.

Once FCoV mutates, the virus gains the ability to invade and replicate inside immune cells (macrophages), spreading throughout the body. This triggers an overwhelming immune response that leads to inflammation, fluid accumulation, and damage to vital organs. This mutated form is referred to as FIPV (FIP virus).

Key Insight:

Not all cats with FCoV develop FIP. Only a small percentage (estimated between 5–10%) of FCoV-infected cats develop FIP, and only when the virus mutates.

Risk Factors for FIP Development

While the FCoV mutation is random, certain conditions significantly increase the risk of FIP development. Let’s explore these in the context of New Zealand and Australia, where both urban and rural environments can contribute to virus spread.

1. Age and Immune System Strength

FIP occurs most commonly in cats under 2 years of age, especially kittens between 4 and 12 months. Their immune systems are still developing, making them more vulnerable to systemic infections. Older cats with compromised immune systems (due to illness or age) are also at risk.

2. Stress and Environmental Changes

Stress plays a critical role in FIP emergence. Common stressors include:

• Moving to a new home

• Spaying or neutering surgery

• Introduction of new animals

• Overcrowding in shelters or batteries
  

In Oceania, where cat rehoming efforts are common and many rescues are active, this is especially relevant.

3. Genetic Susceptibility

Some purebred cats (e.g., Ragdolls, Bengals, Abyssinians, Birmans, and British Shorthairs) appear more prone to developing FIP. This suggests a genetic component to immune response or virus handling. Breeding practices in Australia and New Zealand should account for this vulnerability.

4. High Virus Load

Cats exposed to high amounts of FCoV — typically in multi-cat households or rescue centres — are at greater risk. High viral replication rates increase the chance of a mutation that can lead to FIP.

Types of FIP

Understanding the forms of FIP helps grasp how the mutated virus behaves:

• Wet (Effusive) FIP: Characterised by fluid accumulation in the abdomen or chest, causing swelling, breathing difficulties, and lethargy.

• Dry (Non-effusive) FIP: Involves granulomatous lesions in organs, leading to symptoms like weight loss, neurological issues, and eye inflammation.

• Neurological and Ocular FIP: Affects the brain, spine, or eyes. Often harder to diagnose and treat, but becoming more recognizable due to increased awareness and diagnostic testing.

Both wet and dry forms stem from the same mutation event of FCoV to FIPV, but vary based on how the immune system responds.

Diagnosing FIP: The Challenge

Because many healthy cats carry FCoV and because symptoms of FIP can mimic other diseases (such as cancer, toxoplasmosis, or bacterial infections), diagnosis can be difficult. There is no single definitive test for FIP, especially in its dry form.

Veterinarians typically rely on:

• Clinical signs

• Blood tests (e.g., elevated globulins, low albumin: globulin ratio)

• Ultrasound or X-ray for fluid

• Rivalta test (for fluid evaluation)

• PCR testing (to detect FIPV RNA in tissue or fluid)
  

In Australia and New Zealand, advanced testing may be limited in rural areas, making clinical suspicion even more important.

Preventing FCoV and Reducing FIP Risk

Although it’s not possible to eliminate the risk of FIP, the following strategies help reduce FCoV exposure and mutation chances:

• Maintain good hygiene: Regular cleaning of litter trays, food bowls, and bedding.

• Avoid overcrowding: Especially in foster homes, catteries, and shelters.

• Minimise stress: Allow gradual acclimatisation to new environments or other animals.

• Early weaning caution: Avoid separating kittens from their mothers too early, as maternal antibodies help prevent early infections.

• Test and monitor: For breeders, routine screening for FCoV can help track high-risk lines.
  

Vaccination for FIP exists but is not widely used or recommended in Oceania due to limited efficacy and availability. Instead, focus is placed on proactive environmental and health management.

Final Thoughts: Awareness Saves Lives!

FIP is a complex disease with tragic outcomes if left untreated. However, early recognition, awareness of FCoV, and risk factor reduction can make a real difference. Thanks to emerging antiviral treatments like GS-441524 and increasing global awareness, many cats diagnosed with FIP today can recover and live full lives.

At Cure FIP Oceania, we’re committed to supporting cat owners, breeders, and veterinarians in New Zealand and Australia with the latest science-based knowledge and effective treatment access. If your cat has been diagnosed or you're concerned about symptoms, don’t hesitate to reach out to our expert team.