Table 5.
Uses of FCoV antibody testing
| Reason for testing | Positive result | Negative result | Desirable criteria in FCoV antibody test and other comments | |
|---|---|---|---|---|
| 1 | To rule out a diagnosis of effusive FIP | Does not necessarily indicate FIP, as many sick cats may be seropositive for FCoV owing to a prior transient infection | Rules out FIP unless test is insensitive or inhibited by large amounts of virus | Good sensitivity: because a negative result is more useful than a positive. Specificity is also important to avoid erroneous FIP diagnoses. Useful to have test which works on effusion. Essential that the test works in presence of large amounts of virus |
| 2 | To rule out a diagnosis of non-effusive FIP | Does not necessarily indicate FIP, as many sick cats may be seropositive for FCoV owing to a prior transient infection | Rules out FIP unless test is insensitive | Sensitivity matters, although most dry FIP cases have a very high antibody titre. A negative test is more useful than a positive result. |
| Specificity is very important to avoid mistaken FIP diagnoses. Using a small amount of sample is an advantage | ||||
| 3 | To monitor FIP treatment | Re-test in 2–3 months; continue treatment, gradually reducing corticosteroid dose, if applicable | Provided clinical signs, haematology and biochemistry parameters have returned to normal, it is now safe to discontinue treatment | Less useful than monitoring AGP, globulin, lymphocyte count and haematocrit in early stages, but good for knowing when to stop treating a recovered cat. FCoV antibody titre essential: hoping for decreasing titre if treatment effective. Not useful to test more frequently than every 8–12 weeks. Bear in mind that high doses of steroids can artificially reduce the FCoV antibody titre, so interpret results with caution |
| 4 | Diagnosis of FCoV associated with gastrointestinal signs | The clinical signs may be related to FCoV infection, but as many cats with diseases other than coronaviral enteritis will also be seropositive, other parameters must be examined and differential diagnoses carefully eliminated | Provided the test is sensitive enough and that the kitten or cat had time to seroconvert (ie, at least 3 weeks) FCoV or FIP are unlikely to be the causes of the gastrointestinal signs | Negative result is more useful than positive; therefore, good sensitivity essentialA positive test can be followed up with RT-PCR of the faeces to establish if virus is being shed |
| 5 | To check cats in contact with FIP case or known FCoV excretor | Positive result expected, especially where litter trays are communal. Re-test every 2–3 months until negative. Minimise virus dose exposure and stress, and optimise nutrition to try to avert development of FIP | No risk of FIP (unless test has poor sensitivity) and safe to introduce a new cat | Guardians of an FIP cat often have two questions about the survivor(s): 1 Will the survivor(s) develop FIP? As the chances are that the cat will be seropositive and will be monitored, a test that gives a FCoV antibody titre is best first choice 2 Is it safe to get another cat or is the survivor going to infect him or her (see row 6)? |
| 6 | Screen household of cats before bringing in a new kitten or cat | If the cats in the household are seropositive, it is not advisable to introduce another cat, especially if it is FCoV seronegative | If the cats in the household are negative, it is safe to bring in a seronegative cat but not a seropositive one | Any kind of test can be used, provided sensitivity and specificity are good. If positive – see row 8 for how to proceed |
| 7 | Screen cat before entry into multi-cat household or FCoV-free country | If the cats in the household are negative, it is not advisable to admit a seropositive cat | If the cats in the household are seropositive, it is not advisable to admit a seronegative cat | In-house positive/negative tests suitable for this purpose, provided adequately sensitive |
| 8 | In a household in which FCoV is being eliminated FCoV antibody testing is used to separate infected and uninfected cats | Re-test antibody titre in 2–3 months (in kittens <6 months old, re-test in 1 month). Consider testing faeces by RT-PCR | This cat has eliminated FCoV, provided the test was sensitive enough. Separate the cat from cats that are still seropositive | Antibody titre essential for this purpose: the higher the antibody titre, the greater the chance that the cat is shedding virus. The seropositive cat has an approximately 1 in 3 chance of being actively infected (ie, 66% of seropositive cats are actually not shedding virus at any one time) |
| 9 | Screen stud cat prior to mating | May be shedding FCoV; therefore, use controlled matings to prevent virus transmission.* Faeces can be tested for virus | FCoV-free (provided test is sensitive enough); therefore, preferably use FCoV-free queen | Speed may be required. In-house positive/negative tests suitable for this purpose, provided adequately sensitive |
| 10 | Screen queen cat prior to mating | May be shedding FCoV; therefore, delay mating until cat becomes FCoV-free or use controlled matings to prevent virus transmission. Take steps to prevent infection of kittens. Test faeces for virus | FCoV-free (provided test is sensitive enough); therefore, preferably use FCoV-free stud. No risk of virus transmission to kittens | A rapid result is often required. In-house positive/negative tests suitable for this purpose, provided adequately sensitive. Specificity is also important |
| 11 | Screening kittens of a FCoV seropositive queen to check whether they have become infected | Have become infected with FCoV, so should not be rehomed in household with uninfected cats – rehome where only cat. Re-test monthly. The kitten has around a 1 in 10 chance of developing FIP | FCoV-free (provided test is sensitive enough); therefore, no risk of FIP developing | Test kittens after 10 weeks of age. 22 Sensitivity of the test is important, as is the ability to detect low levels of FCoV antibody |
| 12 | Screen cat prior to stressful procedure; eg, rehoming, neutering or other elective surgery | If possible, delay the stress until the cat has become seronegative. Re-test in 2–3 months | FCoV-free (provided test is sensitive enough); therefore, no risk of FIP developing | In-house positive/negative tests suitable for this purpose, provided they are adequately sensitive, but positive cats will need FCoV antibody titre to monitor becoming seronegative. See comments in row 8 |
| 13 | Screen cat prior to immunosuppressive treatment; eg, high-dose steroids, ciclosporin A, chemotherapy | If feasible, RT-PCR test faeces to determine if actively infected. If so, delay the treatment until the cat has become negative. Re-test FCoV antibody titre in 2–3 months | FCoV-free (provided test is sensitive enough); therefore, no risk of FIP developing | In-house positive/negative tests suitable for this purpose, provided they are adequately sensitive, but positive cats will need a follow-up test to establish FCoV antibody titre. RT-PCR testing can be useful, but five consecutive negative tests required to establish that the cat is no longer infected 3 |
| 14 | Screen a prospective blood donor cat prior to transfusion | Use of FCoV seropositive blood donor is not recommended | Safe to use a FCoV seronegative blood donor, provided test is sensitive enough | Speed is usually essential, so in-house tests are likely to be chosen. There is some evidence that passively transferred FCoV antibody could endanger the recipient in the event of becoming infected with FCoV23,24 |
| 15 | Screen cat prior to FIP vaccination | No point vaccinating: the cat is either incubating FIP already or has natural immunity3,25–27 | Vaccinate | Rapid result usually desired, so in-house tests usually chosen. There is no point in vaccinating a seropositive cat with the FIP vaccine, as the cat has already been exposed to infection |
| 16 | Screen prior to FeLV vaccination | Vaccination not recommended; either screen faeces for FCoV virus shedding or wait 2–3 months and re-test for FCoV antibodies | Safe to go ahead and vaccinate, provided test is sensitive enough | In-house tests usually chosen. There is concern among cat breeders that FeLV vaccination of FCoV-infected kittens can trigger FIP; therefore, a pre-vaccination screen of rescued cats or pedigree kittens for FCoV infection is advisable |
FIP = feline infectious peritonitis; FeLV = feline leukaemia virus; RT-PCR = reverse transcriptase polymerase chain reaction; AGP = alpha-1-acid glycoprotein
*
Controlled matings are where the stud and queen are put together for only the time needed to mate. The cats are not left together and do not have contact with a litter tray, so are not exposed to each other’s faeces