Feline Immunodeficiency Virus (FIV):
The FIV DNA Confirmatory Test

FIV (Feline Immunodeficiency Virus) screening is currently done using an ELISA kit which will detect the anti-FIV antibodies in a cat’s blood by having them bind to FIV antigens in a microtitre plate. Antibodies that do bind are labeled with a colour-producing probe and the change in colour of the solution in the well is read by a spectrophotometer. The intensity of the colour is a direct indicator of the amount of anti-FIV antibody in the cat’s serum.

Problems with this method are four-fold. First, antibody levels must be above a certain threshold to generate a positive result. Second, antibody specificity may vary, and non-specific binding to non-FIV antigens may occur, producing a false positive. It is not known if cats can clear FIV once exposed. Therefore, a positive antibody test is not necessarily diagnostic of FIV infection. It is only diagnostic of exposure. Finally, passive transfer of maternal antibodies may result in a positive test in a kitten which is not infected.

Most samples positive by ELISA are confirmed using the western blot. The western blot will confirm that the circulating antibodies are specific to FIV structural proteins. This still leaves the other issues unresolved.

Part of the solution lies right in the virus itself. The genetic material of FIV is RNA. Once the virus infects a cat’s blood cell, it makes a DNA copy of its RNA genome and inserts this copy into the DNA of the host cell. DNA from feline blood cells can be extracted and tested to determine if any of these cells have been successfully infected with FIV. Using a technique called the Polymerase Chain Reaction (PCR), it is possible to make millions of copies of sequences specific to FIV, and then visually detect the PCR products. PCR-based testing is extremely sensitive and highly specific, markedly reducing the chance of false positive and negative results.

VITA-TECH Canada Inc. has been using PCR technology for the detection of genetic diseases and infectious agents, such as bacteria, parasites, fungi and viruses, in various animals since 1995. We proudly announce that after several test trials we can confidently replace our western blot confirmatory test for FIV ELISA positives with the more sensitive and highly specific FIV DNA test.

If you have any questions regarding the FIV or any other DNA-based tests, please feel free to give us a ring (or an e-mail at info@vita-tech.com).

Reference: Rimstad E & Ueland K (1992) J Virol Meth 36: 239-248