Three groups of cat sera were studied to validate the FIP 7B test from: 1) 10 laboratory cats exposed to two different FIPV strains (4 cats), FECV (2 cats), FIP Vaccine (2 cats), and SPF controls (2 cats); 2) 12 cats with FIP-PCR +, histopathology confirmed FIP; and 3) 20 cats of two different catteries of 10 each followed, to track the progression of FIPV exposure.

Results from Group 1) cats showed that 4 of the 5 FIP and FECV infected, and both of the FIP vaccinated cats had high coronavirus IFA titers (1:960-1:4096) but only the FIPV infected cats were FIP 7B-ELISA positive (1:160-1:640). The SPF pathogen-free control cats were negative for both tests and one FIP exposed cat remained uninfected. Group 2) cats all had FIP 7B-ELISA titers varying from 1:160-1:640 and all 12 cats died of FIP. Group 3) cats showed a clear association between detectable FIP 7B-ELISA titers (>1:80) and eventual outcome of clinical FIP and death within 3 months of testing. None of the 12 cats with negative 7B titers in these two catteries developed disease during the 3 month test period.

Cats infected with a variety of coronavirus strains were studied by an independent laboratory to compare results with the routine IFA assay and the new FIP 7B-ELISA. Ten cats were vaccinated with an experimental coronavirus vaccine, all rapidly became IFA positive but none were 7B-ELISA positive. All 10 cats were then challenged with virulent FIPV. Nine of the 10 cats gradually became FIP 7B-ELISA positive while remaining IFA positive.

A second study involved 22 FIV positive cats infected with an FECV strain. All 22 cats rapidly became IFA positive but none were 7B-ELISA positive.

Lastly, of 124 cats followed from multicat households or catteries, 120 had positive IFA titers but only 32 (26%) were also FIP 7B-ELISA positive. These cats are being monitored for evidence of clinical FIP.

Preliminary data indicate that FIP 7B-ELISA titers of 1:160 or higher mean that the cat has FIPV infection. Titers 1:320 or higher suggest that about 50% of these cats will die of FIP within 3 months. Lower titer cats (1:80 or less) would not be expected to show clinical FIP or die within 3 months, and cats testing negative are expected to be free of FIPV. We recommend that cats with low titers have a repeat test run in 1 month. Also, early data in catteries with persistent shedding of FECV show that the potential to develop FIP exists when these cats are coinfected with FIV or are immunosuppressed.

Of 100 cases analyzed to date, the Positive Predictive Value of FIP 7B-ELISA approaches 100%. When larger numbers of cats are evaluated, the Positive Predictive Values of the population would be expected to be somewhat lower. As with any new test, its true value will be known only after thousands of cases are tested over several years. Nevertheless, we believe that the new FIP-Specific ELISA offers a considerably improved serologic diagnosis of FIPV exposure than the routine feline coronavirus IFA test.

Antech Diagnostics will continue to offer the routine IFA test, but it will be renamed the Feline Coronavirus (FCV)-IFA test, rather than the old name of FIP-IFA test. The FCV-IFA Test will now be performed only at two dilutions: 1:400 and 1:1600. Results of both titers will be reported with the following possible outcomes: