Update on FIP Tests

Antech Diagnostics presently offers two serologic tests and one molecular biology-based, polymerase chain reaction test to aid in the diagnosis of feline infectious peritonitis (FIP):

• Feline coronavirus IFA (FCV-IFA) is a serologic test detecting antibodies to coronaviruses. This test is sensitive but certainly not specific for FIP (see "New Coronavirus Exposure Titer").
• FIP Polymerase Chain Reaction (FIP-PCR) detects the expression of the 7b gene, and measures antigen. The expression of this gene is specific for pathogenic coronavirus (FIPV). It is specific and works well on effusions, but lacks sensitivity when performed on whole blood.
• FIP-Specific ELISA (FIPSE) is a serologic test which detects antibodies against the protein that is encoded for by the 7b gene (i.e. the 7b protein). By focusing on the 7b protein this test has markedly enhanced specificity for FIP when compared to the FCV-IFA. As with all serology, it must be interpreted in conjunction with patient history and clinical signs.

Following the introduction of the FIPSE, Antech Diagnostics embarked on an additional six-month prospective study of 28 cats with positive FIPSE titers. All cats were FeLV/FIV negative. Each cat was titered monthly for FIPSE. Routine bloodwork was evaluated initially and at the onset of any signs of illness. FIP was confirmed by histopathology with or without PCR on all cats that died during the study period. While the study is ongoing, the following observations have been made:

• Monthly titers often fluctuated.
• 57% of cats became negative by FIPSE during the study. Of cats with low positive titers (1:40 and 1:80), 75% became FIPSE negative. Of cats with higher titers (1:160 and 1:320), 14% became negative. All of these seronegative cats remain clinically healthy.
• 11% of cats in the study died of FIP. Of cats with low positive titers (1:40 and 1:80), 5% died. Of cats with higher titers (1:160 and 1:320), 25% died.
• Three cats died of FIP (one non-effusive, two effusive). These cats entered the study without clinical signs, but with FIPSE titers of 1:160, 1:80, and 1:320. When they died, their titers were 1:160, 1:80 and 1:80, respectively. All had hyperglobulinemia, hypoalbuminemia, and anemia. These laboratory findings were present weeks before the onset of clinical signs in two of the cases.
• 32% of cats remain seropositive and are all healthy to date.
• FIPSE titers indicates exposure to FIPV, but seropositivity does not necessarily predict disease.

Selection of the appropriate test for each case is dependent on the clinical situation. In addition to your standard clinical database, the following recommendations can be made:

* For cats with effusive disease, perform PCR testing on the effusion. Be sure to submit a fresh specimen in a LTT, which has been refrigerated and sent on an ice pack. For optimal recovery of the antigen (RNA), this should not be added on to a specimen previously submitted for fluid analysis. A FIPSE run on effusive cases may provide you with quicker turn around time, but please note that a small percentage of cats with effusive FIP may be negative on the FIPSE test just as they may be negative on the FCV-IFA.

* For cats that have non-effusive disease and are FIP suspects, submit FIPSE (serum, RTT or STT only, no LTT) to document exposure to FIPV. If the cat has granulomatous disease for which you are submitting biopsies, consider running PCR on fresh tissue samples. These should be submitted in a small amount of saline in a plain red top tube and kept cold. (LTT should not be used for FIPSE, as it may interfere with the reaction.)

* For cats with known exposure to FIP, consider running FIPSE (serum only) at least 3 weeks after the last known contact. If the test is positive, it documents immunologic response, but clinical outcome cannot be predicted by a single positive test. These cats should be followed over time, both clinically and with laboratory data.

* For healthy new cats coming into a household, consider running both the FIPSE to document prior exposure to FIP and the Exposure Titer #5342 to document exposure to enteric coronavirus. While a cat may be negative on the FIPSE, if it has been infected with enteric coronavirus it is still potentially at risk for viral mutation and developing FIP. Therefore, a coronavirus positive cat entering a multicat household may create risk for all felines in the household.

* Vaccinating cats for FIP may produce a positive FCV-IFA titer, but vaccination will not affect the FIPSE.

Of 28 cats in Antech's prospective study, 16 gradually became 7b antibody negative and all remain alive and healthy 6 months later. The remaining 12 cats have continued to be 7b positive; 3 of them have died of confirmed FIP (a 25% death rate during the study period). An additional cat in this 7b antibody positive group remains healthy but gave birth to kittens which promptly died of FIP, indicating active carrier status of their dam. These results clearly show the risk of developing clinically active FIP when 7b serology is positive, and demonstrate the prospective value of the test. Incidentally, all 28 cats in this study have been consistently coronavirus (FCV-IFA) positive, emphasizing the relative lack of prospective value of this assay.

* Antech now offers a new Cat Scan with FIPSE that replaces the FCV-IFA with the FIPSE. The cost for the profile (test code #1384) is $44.00.

We are most grateful to Drs. Lori Goeders and Caryl Handleman, Antech consultants, and to the veterinarians and cat owners who participated in this study.

Based on recent studies at Antech and in response to our clients' concerns about the sensitivity of our IFA assay to detect exposure to coronavirus, we are updating the dilutions performed in the FCV-IFA assay. To establish the appropriate dilutions, we performed the FCV-IFA assay on serum from 20 pathogen-free cats. Non-specific reactions were detectable at very low titers but all cats were negative for exposure to coronavirus. We will therefore continue to run the FCV-IFA assay at a 1:400 and a 1:1600 dilution, but will also offer a separate lower dilution test for coronavirus exposure at 1:25 only. Cats with titers <1:25 are considered serologically negative for exposure to coronavirus. A POSITIVE TITER AT 1:25 DOES NOT INDICATE THAT THE CAT HAS FIP; ONLY THAT IT HAS BEEN EXPOSED TO A CORONAVIRUS.

+ = Positive
­ = Negative
ND = not done

Notice on FIV Price Increase

The FIV assay was developed at University of California, Davis which transferred patent rights to a licensee. Due to patent issues and related costs with the licensee, we have been forced to increase our FIV price by $2.50 per test effective January 1, 1999.

We apologize for this increase and trust that you will appreciate that the circumstances were beyond our control.