Feline infectious peritonitis (FIP) is caused by a mutated version of a feline coronavirus that transforms from a benign, minimally pathogenic virus to an aggressive and deadly version. Feline infectious peritonitis (FIP) is a devastating diagnosis for a cat owner as the disease is considered 100% fatal.
FIP is considered an incurable disease and the mainstay of treatment has focused on providing comfort and supportive care to affected patients. Since FIP is a deadly disease, there have been many efforts to develop effective treatments for it, with disappointing results.
However, progress is being made in developing new therapeutic options for FIP in cats. Researchers at Kansas State University devised a new antiviral treatment, which led to full recovery in cats experimentally infected with FIP who were treated at a stage of disease that would otherwise be fatal.
The antiviral treatment works by blocking the replication of the virus, a process required for it to survive within an infected cat. Six out of eight cats treated with the antiviral had resolution of fever, ascites, and low white blood cell counts, and returned to normal health within 20 days or less of treatment.
More on the experimental treatment below, but first, a primer on FIP.
Clinical Signs of FIP
Cats with FIP show non-specific signs of illness, including lethargy, inappetance, and weight loss. They may present with persistent fever and owners can notice abdominal distension or difficulty breathing in cases where fluid build-up within body cavities (effusion) is present.
There are two clinical forms of FIP recognized in cats: the “dry form” (noneffusive) and the “wet form” (effusive). In the dry form of the disease, cats develop mass-like lesions within their abdominal and chest cavities called granulomas. In the wet form of the disease, cats show fluid buildup in these same anatomical regions. There can be overlap between the two forms; cats with the effusive form often can have microgranulomas present and cats with the dry form can develop effusion.
Diagnosing FIP is difficult, and your veterinarian will likely recommend several tests to determine what is causing your cat’s signs.
Radiographs (x-rays) can help determine if fluid is present within the abdominal or chest cavities. An ultrasound can show enlarged lymph nodes or granulomas within the abdomen and confirm the presence of fluid. Bloodwork may be normal, but one of the most consistent findings is an elevation of a specific protein called globulin.
There is a blood test that measures whether or not a cat has circulating antibodies to the feline coronavirus, but this test is considered of limited utility. Most cats with circulating antibodies never develop FIP. High amounts of antibody make FIP a likely diagnosis, but 10% of cats with FIP will not have circulating antibodies in their bloodstream.
If effusion is present, analysis of this fluid will show a high protein level along with a relatively low cell count. In cats with nervous system involvement (e.g., brain and/or spinal cord), MRI or CT of the brain can show changes including hydrocephalus, which is a build-up of fluid in the brain. Analysis of the pet’s cerebrospinal fluid (CSF) will show high protein and cell counts.
The most reliable test for FIP is detecting the feline coronavirus antigen within white blood cells of the affected patient by special stains.
Treating FIP Experimentally
As I mentioned at the beginning, FIP is considered incurable, with treatment consisting mainly of providing comfort and supportive care. For cats in respiratory distress from fluid buildup around the lungs or within the abdomen, removing the effusion and providing oxygen support can aid in immediate relief.
Though the experimental antiviral treatment at Kansas State University seems promising, there is concern that the coronavirus that causes FIP could acquire further mutations, rendering it resistant to antiviral treatments such as the one developed at Kansas State University. In addition, this form of treatment was only studied in cats with the effusive form of the disease; its efficacy in cats with the dry form is unknown. It is also unknown whether the antiviral will be successful in treating cats naturally infected with FIP as all of the cats in the study were infected experimentally.
Polyprenyl Immunostimulant (PI) is an investigational biologic used to lessen clinical signs associated with herpes virus infections in cats by promoting immune responses to the virus. PI also has been used to treat FIP. In a small study, three cats with the dry form of FIP were treated with PI. Two cats were alive and still receiving treatment two years following diagnosis. The remaining cat was treated for only 4.5 months and lived a total of 14 months. A larger study was done in 58 cats with the dry form of FIP. Five percent of those cats lived longer than one year and 22 percent lived at least 5.5 months.
Though PI might seem like the magic bullet for treating the dry form of FIP, there are a few caveats to consider. In the smaller study, the amount of disease present in all three cats was minimal; two had no clinical signs at their time of diagnosis. In the larger study, cats who were very ill or died within a week of starting treatment with PI were excluded from the survival analysis, likely skewing results.
As some cats with no or minimal signs of disease and localized lesions can spontaneously recover from FIP without treatment, the role of PI in aiding the convalescence in these marginally affected cats is unclear. PI is also completely ineffective in treating cats with the effusive form of FIP.
Though these new treatment options seem promising, further research is necessary to determine how successful they will be for cats affected with FIP.
Controversy exists concerning the efficacy of an intranasal vaccine to prevent infection with FIP. The vaccine it is not thought to be effective in preventing disease in cats previously exposed to feline coronavirus, but it may induce some level of protection for a cat that has never been exposed to the virus.