Feline Coronavirus or Feline Infectious Peritonitis (FIP)

24 05 2011

Feline Coronavirus or Feline Infectious Peritonitis (FIP)

Feline Infectious Peritonitis (FIP) or feline enteric coronavirus is widespread within the feline population with both domestic and exotic cats being affected. The virus is a RNA containing coronavirus.  Ninety percent of cats in catteries have antibodies to this virus whereas 50% of cats in single-cat homes have antibodies to the virus. Although exposure to feline coronavirus is high, clinical disease affects only small numbers of animals.

There are several strains of Feline coronavirus.  These strains vary widely in their virulence (ability to cause disease).  Less virulent strains multiply in the intestinal epithelium.

With the more virulent strains of coronavirus, the virus undergoes a mutation allowing it to multiply in macrophages (type of white blood cell).  This virulent mutation appears to be the key in the development of clinical FIP.  The population density of cats in a household is a major factor involved in the likelihood of this mutation occurring.  In fact, the majority of clinical cases of FIP come from infected catteries, shelters or households with a population density of 5 or more cats.  The mutation probably occurs due to stress-associated immunosuppression and exposure to multiple strains of the virus.  It is estimated that up to 20-35% or more of the cat population may be infected with the coronavirus but less than 1% will develop clinical FIP.  The mortality rate can go up to 35% in some breeding catteries and households with multiple cats.

The presence of feline coronavirus may not be detected clinically for months or even years after initial infection.  The virus may remain dormant until such time that the animal is stressed.  Antibodies that are typically produced by a cat’s immune system to fight infection actually promote the development of clinical disease.

There also appears to be a genetic influence regarding the susceptibility to coronavirus infection.

FIP is spread primarily by a fecal-oral route and less commonly by an oral-nasal route (inhaled). In addition, a case of transplacental transmission (from mother to kitten) has been documented.  The virus is typically spread in the feces of infected cats and is transmitted to susceptible individuals through oral consumption of the virus on contaminated coats or environmental fecal contamination.  Feline Coronaviruses can survive for 4- 6 weeks within dried feces in the environment. The virus may be destroyed by most household disinfectants and is particularly susceptible to household bleach at a 1:32 dilution.

Cats with FIP often have a history of failure to thrive. Cats less than two years of age and those cats over 13 years of age appear to be the most susceptible to the virus.  These cases are often typified by an antibiotic-unresponsive fever, are lethargic, jaundice, with possible abdominal masses and/or neurologic signs.  Cats may have ocular involvement including anterior uveitis (infection in the anterior eye chamber), hypopyon (accumulation of pus in the anterior eye chamber), hyphema (blood in the anterior chamber) or retinal hemorrhage or detachment.  Three distinct forms of clinical FIP are possible.

Cats with the “wet form or effusive form” of the disease will develop a yellow-tinged, high-protein, sticky inflammatory exudate called a transudate in their abdominal, pleural (chest), pericardial (around the heart), or scrotal cavities. The transudate is actually caused by the cat’s antibody production to the virus which is not protective and will aggregate in immune complexes causing a vasculitis and the subsequent characteristic effusion (the protein fluid characteristic of effusive FIP).   Pleural effusion (FIP transudate in the chest) will cause dyspnea (difficulty in breathing), were as ascites (fluid accumulation in the abdomen) may be seen as abdominal enlargement.

Cell-mediated immunity is necessary to deter the development of clinical FIP.  The “dry or granulomatous form” of FIP is noneffusive (does not produce an inflammatory exudate) and is characterized by granulomatous lesions in the abdominal organs, lungs, eyes and brain and is believed to be a result of a partially protective cell-mediated immune response that is unable to wall off and contain the virus..  These cats may have a history of vague illness, chronically high fevers of unknown origin that are non-responsive to antibiotics and have chronic weight loss.

The neurologic form of FIP is less commonly encountered. Around 40% of these cases will only have clinical signs related to the central nervous system Clinical signs include seizures, ataxia (appear unbalanced), paresis (weakness), paralysis, vestibular disease, peripheral neuropathy (loss of sensation and tingling), hyperesthesia (increased sensitivity to touch), urinary incontinence and behavior changes.

Serum biochemistry often shows high serum protein level of greater than 8.0 g/dl. An anemia secondary to red blood cell destruction (hemolysis) is common. Affected cats may exhibit severe liver disease seen by elevated bilirubin levels causing the cat to appear jaundice.

Presumptive diagnosis is often based on the characteristic history, clinical signs and laboratory findings.  Wet FIP diagnosis may be made through the analysis of the effusive fluid.  The protein content of the effusive fluid is high (5-12 g/dl), the specific gravity of the fluid is typically 1.017 – 1.047.  The fluid is composed of a mixture of inflammatory white blood cells including neutrophils, lymphocytes and macrophages.  When an albumin/globulin ratio of the effusion is less than 0.45 it is characteristic of effusive FIP.

Dry FIP is more difficult to diagnose.  The cats in both wet and dry forms of the disease will typically have low lymphocyte counts (lymphopenia), high numbers of neutrophils (leukocytosis) of greater than 19,000 cells µl, with high levels of globulin (hyperglobulinemia) in the blood of greater than 5.1 g/dl.  The serum protein level is greater than 7.8 g/dl in the plasma of 70% of the feline clinical cases of dry FIP and in approximately 50% of the cases of wet FIP.  A history of a high fever that is non-responsive to treatment is also characteristic of infection with dry FIP.

Many of these cats may also be infected with Feline Leukemia Virus (FeLV) or Feline Immunodeficiency Virus (FIV). Serology testing will easily confirm the presence of a complicating viral infection.

Serologic tests for coronavirus antibody are not specific for clinical FIP.  Serologic tests do not differentiate clinical from nonpathogenic forms of feline infectious peritonitis.  Increasing or high titers are often helpful in diagnosis but it is not unusual for some cats with clinical FIP to have negative or very low titers.  In general these tests are considered to be unreliable for the confirmation of clinical FIP. Definitive diagnosis of FIP requires detection of feline coronavirus within macrophages in effusions (body fluids) or within lesions detected in affected tissues.

Virtually every cat with clinical FIP dies within a short time period.  Interferon has been used to treat cats but the efficacy of its use in treatment has not yet been determined.  Prednisone and cyclophosphamide are immunosuppressive drugs that may slow the disease progression but will not produce a cure.  Supportive care may be provided as long as the pet is comfortable and still has quality of life.   Supportive care may include antibiotics for secondary infection and fluid therapy for dehydration.  The chest may be drained of fluid to relieve acute respiratory distress but it only provides temporary relief. Most cases of clinical FIP will end with euthanasia.

One vaccine is currently available for the prevention of FIP.  The vaccine is manufactured by Pfizer Animal Health and is licensed for the vaccination of cats 16 weeks and older. According to studies it protects 60 to 90% of the cats vaccinated. Protection from the vaccine is due to IgA (local antibody) which neutralizes the virus before entry to the body.  The duration of protection is believed to be limited. The Feline Advisory Panel does not generally recommend vaccination.  Most members of the Feline Advisory Panel agree that the vaccine is safe but there is considerable controversy among panel members as to the efficacy of vaccination.  In general, cats that are seronegative for feline coronavirus at the time of vaccination are the cats most likely to develop protection from this vaccine.  It is believed most kittens born and raised in environments in which coronavirus infections are endemic will be infected prior to reaching 16 weeks of age consequently making the vaccine ineffective.

Within a cattery other measures to reduce exposure include:  frequent removal of feces (the primary source of coronavirus), early weaning of kittens, isolation of cats that test positive for coronavirus antibodies, proper sanitation, and cleaning with disinfectants that will inactivate the virus, are all steps that will help to limit exposure.  Increasing the number of litter boxes to one per two cats and reducing overcrowding will greatly reduce FIP losses.  No healthy cat should be euthanized for a positive coronavirus titer on antibody testing.

In multiple-cat households approximately 5% of coronavirus infected cats will develop clinical FIP.  In single-cat households less than 1% of coronavirus infected cats will develop clinical FIP.  The incidence of FIP appears to be higher in certain genetic lines so whenever possible pedigree analysis should be conducted so that only FIP-resistant breeding stock is used in a cattery.

References:

Ettinger, Stephen DVM and Edward C. Feldman DVM.  Textbook of Veterinary Internal Medicine. 6th Edition 2005, Elsevier, Inc. pp.663 – 666.

Kahn, Cynthia Editor. The Merck Veterinary Manual. Merck Co. 9th Edition. 2005. Pp.628 – 631.

Norsworthy, Gary.   Mitchell Crystal. Et al.  The Feline Patient.  Blackwell Publishing 3rd Edition.  2006.  Pp. 97 -98.

Pfizer Veterinary Services.  Conversation 2/19/08.

The 2006 American Association of Feline Practitioners Feline Vaccine Advisory Panel Report.  The Journal of the American Veterinary Medical Association, Vol 229, No. 9, November 1, 2006. Pp1405-1435.

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