Additional testing for FIP
Antibody testing. Many veterinary laboratories provide qualitative and quantitative testing for feline coronavirus antibodies in serum. An in-clinic
ELISA test is also available and can be performed on serum or plasma. These tests cannot differentiate cats with exposure
to the harmless enteric form from those with FIP. Negative results strongly discount FIP infection, but a positive titer has
little diagnostic value unless it is more than 1:1,600.6
It is interesting to note that titers can fall dramatically in the terminal stages of the disease. Efforts have been made
to improve the specificity of serologic tests for FIP, including the development of an assay for antibodies against the 7b
protein of feline coronavirus. This antigen was thought to be associated with FIP viral strains but is also expressed by the
enteric biotype. Thus, positive results with the FIP 7b ELISA test should not be regarded as definitive evidence of the disease.7
PCR testing. A polymerase chain reaction (PCR) test for identification of feline coronavirus messenger RNA (mRNA) is offered through several
commercial laboratories. The concept behind this test is that the presence of mRNA indicates active viral replication within
the body, which would be indicative of FIP rather than enteric feline coronavirus infection.8 The test can be performed on whole blood, cavity effusions, or aqueous humor.
Conflicting reports exist regarding the reliability of this test, and it seems as though results from the testing of whole
blood are questionable. In one report, more than half of the healthy control group had positive results, suggesting poor specificity.9 However, real-time testing of effusions appears to be much more reliable and can accurately differentiate cats with FIP
from those with other causes of ascites or pleural fluid.6
Immunocytochemistry and immunohistochemistry. Samples of effusion or affected tissues may be tested for the presence of viral antigens using anti-FIP antibodies.10 Essentially, polyclonal or monoclonal antibodies with high specificity for the feline coronavirus are mixed with the sample
and allowed to attach to infected macrophages. The antibodies are subsequently detected using a marker agent, either fluorescein
(effusion or fresh tissue) or horseradish peroxidase (formalin-fixed tissue).
These tests are generally regarded as the diagnostic gold standard, and a positive result is definitive confirmation of FIP.
Unfortunately, false negative results may occur when low cellularity effusions are tested or if unaffected organs are biopsied.2
Most experts regard FIP as an incurable disease, although some cases of apparently spontaneous remission have been reported.
Numerous medical therapies are described in the literature, usually with conflicting accounts of efficacy. It seems likely
that some medical interventions have a positive effect, but such responses are generally transient, and owners should always
be informed of the grave prognosis associated with FIP.
Administering glucocorticoids appears to improve survival times in cats with FIP and may mitigate morbidity associated with
fever and hyporexia. Giving other immunosuppressive agents, such as cyclophosphamide or chlorambucil, appears to offer little
advantage and may cause myelosuppression.2
Feline interferon omega administration was reported to induce remission in one study but showed no benefit in a larger population
of affected cats.11,12
Pentoxifylline therapy has been suggested because it inhibits tumor necrosis factor alpha and has an antivasculitis effect;
however, a recent placebo-controlled study using a related agent failed to identify a positive effect in cats with FIP.13
The administration of various antiviral agents has demonstrated efficacy against feline coronavirus in vitro, but we are not
aware of any reports describing their effects in cats with experimental or spontaneous infections.14
A report published in 2009 described the effect of Polyprenyl Immunostimulant (Sass & Sass) administration in three cats with
dry FIP.15 The findings were encouraging, as two of the three cats were alive > 24 months after diagnosis. This product is thought
to upregulate innate immunity and is marketed for the reduction of clinical signs in cats with rhinotracheitis.