COMPETITIVE REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION FOR QUANTITATION OF FELINE IMMUNODEFICIENCY VIRUS

A competitive reverse transcription-polymerase chain reaction (RT-PCR) was developed to quantify RNA of feline immunodeficiency virus (FIV) in cats. The assay uses in vitro synthesized RNA derived from the gag region of the FIV genome as a competitive internal control. The synthe sized RNA has a 22-base deletion with respect to the wild-type sequenc e. PCR products were quantitated by densitometric analysis of a digita lized image of the ethidium bromide stained gel. The non-radioactive m ethod was evaluated in reconstruction experiments. RNA synthesis in FI V-infected feline thymocytes correlated well with the amount of viral p24 antigen produced. Viral RNA concentrations in the plasma of two ca ts experimentally infected with FIV strain UT113 were followed for 32 weeks; peak copy numbers (2.3 x 10(4) and 1.3 x 10(4) per ml, respecti vely) were reached 11 weeks after subcutaneous injection of ten 50% ca t infectious doses. With rising antibody titers against FIV-gag and FI V-env gene products, the amount of FIV RNA in plasma decreased. Nine a symptomatic cats that had been experimentally infected 3.5 to 4.5 year s earlier had copy numbers between 5.6 x 10(3) and 4.3 x 10(4) per ml. This quantitative competitive RT-PCR will be useful to study the path ogenesis of the FIV infection, to evaluate the effectiveness of vaccin es and to monitor antiviral and immunomodulating drugs.