Should Felv Test for Cats be conducted on all cats?
All cats should be tested for infection with feline leukemia virus (FeLV) and feline immunodeficiency virus (FIV).
Cats infected with FeLV or FIV may live for many years. A decision for euthanasia should never be made solely on the basis of whether or not a cat is infected.
A confirmed positive test result should be considered only an indication of retrovirus infection, not clinical disease.
Diseases in cats infected with FeLV or FIV may not necessarily be a result of retrovirus infection.
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Felv Test for Cats
No test is 100% accurate at all times and under all conditions. Therefore, all test results should be interpreted in light of the patient’s health and prior likelihood of infection.
Cats Should Be Tested For FeLV Infection Under the Following Circumstances
Whenever they are sick, regardless of age, negative results of previous FeLV test, and FeLV vaccination status.
FeLV infection has been associated with a wide variety of diseases including, but not limited to, anemia, neoplasia, and disorders associated with immune dysfunction.
Although FeLV infection may influence patient management and prognosis, treatment decisions should not be made solely on the basis of whether a cat is infected.
When they are about to be adopted, regardless of age.
Cats should be tested before being introduced into a multiple-cat household to prevent exposing resident cats.
Cats should be tested before being introduced into a household, even if no other cats are present in the household at the time of adoption, for the following reasons:
- FeLV infection may have future health ramifications, even if the cats do not presently have any signs of disease.
- Additional cats may join the household.
- Cats intended to be housed exclusively indoors may escape and expose other cats.
When results of the most recent test are negative, but recent exposure cannot be ruled out.
Cats in this situation should be retested a minimum of 28 days after the last potential exposure, because test results may be negative during the pre-viremic stage of infection.
If the time of the cat’s last potential exposure is unknown, clients should be counseled on the potential risk of exposing other cats in an FeLV-negative household when adding a cat for which results of a single test were negative.
When FeLV infection status is unknown. Infected cats may remain asymptomatic for years, during which time they may serve as inapparent sources of infection to other casts in the household.
When they are exposed, or potentially exposed, to cats of unknown infection status (e.g., cats that go outdoors unsupervised), regardless of whether they have been vaccinated against FeLV.
Periodic testing may be justifiable in cats at continued risk of exposure, even though adult cats are relatively resistant to FeLV infection.
When they are about to be vaccinated against FeLV.
- FeLV vaccines should not be administered to infected cats. FeLV vaccination does not affect the carrier state, the capacity to infect other cats, or the development of disease in casts with pre-existing infection. Vaccination may also be associated with adverse events.
- Cats infected prior to FeLV vaccination may appear to be vaccination failures.
Test Selection
The preferred initial test are soluble antigen test, such as ELISA and other immunochromatographic tests (tests in which color is generated as a result of an immunologic reaction), that detect free antigen in fluid.
Soluble antigen tests are most reliable when serum or plasma, rather than whole blood, is tested.
In experimental settings, most cats will have positive results with soluble antigen tests within 28 days after exposure; however, the time between exposure and development of antigenemia is extremely variable and may be considerably longer in some instances.
Tests using saliva or tears yield an unacceptably high percentage of inaccurate results and their use is not recommended.
Indirect immunofluorescent antibody (IFA) tests detect cell-associated antigen.
Polymerase chain reaction (PCR)-bases assays that detect viral RNA or DNA offer a promising approach to FeLV testing.
However, reagents and testing protocols are neither standardized nor validated.
Test Interpretation
No test is 100% accurate at all times and under all conditions. In populations with a low prevalence of FeLV infection, more than half of cats for which test results are positive are likely to be uninfected.
Confirming positive test results is crucial, especially in asymptomatic cats.
Negative test results are much more reliable than positive results, because of the low prevalence of infection in most populations.
To increase the reliability of a positive soluble antigen test result, the test may be repeated, using a different type of test, such as an IFA test, or another immunochromatograpic test.
Positive results obtained with tests that detect free antigen may be reflective of transient or persistent viremia.
Positive results obtained with tests that detect cell-associated antigen (e.g., IFA test) are highly likely to be reflective of persistent viremia.
Discordant test results are defined as conflicting results obtained with different tests.
Discordancy may be a consequence of the stage of infection, the variability of host response, or technical problems with the testing system.
- If results of two soluble antigen tests are discordant, an IFA test should be performed immediately.
- If results of a soluble antigen test and an IFA test are both positive, the cat is highly likely to be persistently infected.
- If results of a soluble antigen test are positive and results of an IFA test are negative, both tests should be performed again in 60 days and then annually until results of both tests are in agreement. It is very difficult to determine the true infection status as long as discordancy remains, but cats with discordant results should be considered potential sources of infection for other cats.
Because FeLV tests detect antigen rather than antibody, maternally derived antibodies do not influence results of FeLV tests.
Therefore, kittens may be tested at any age.
However, infection in newborn kittens may not be detected until weeks to months after birth.
FeLV vaccination will not induce positive test results. This is all the more reason why you should carry out Felv Test for Cats every 6 months.