DETECTION AND STRAIN DIFFERENTIATION OF FELINE CALICIVIRUS IN CONJUNCTIVAL SWABS BY RT-PCR OF THE HYPERVARIABLE REGION OF THE CAPSID PROTEIN GENE

Reverse transcription-polymerase chain reaction (RT-PCR) was used to d irect the amplification of a 670 to 680 base pair segment that include d the hypervariable regions of the capsid protein gene of feline calic ivirus (FCV). The segment was amplified from 13/13 cultivated FCV stra ins including 12 field isolates collected over 18 years. The sensitivi ties of culture and this RT-PCR for the detection of FCV in conjunctiv al swabs over the course of infection were then compared and correlate d with clinical signs in 5 vaccinated and 3 unvaccinated experimentall y-infected cats. Conjunctival swabs were taken daily from days 0 to 14 and on days 16, 19, 21 and 24 after challenge. FCV was detected in 19 /144 swabs by RT-PCR and 16/144 swabs by culture. Virus detection corr elated poorly with clinical signs regardless of the assay used. The Sa u3AI restriction profiles of the RT-PCR products amplified from both c ultivated strains and clinical samples were compared. All 13 cultivate d isolates, including the 12 field isolates, exhibited different profi les, whereas all profiles from the experimentally-infected cats were i dentical, and matched the profile of the challenge/vaccine strain. Thi s study has established that the RT-PCR assay described is as sensitiv e as culture for detection of FCV in conjunctival swabs, that a broad range of field isolates can be detected and rapidly differentiated by restriction endonuclease digestion, and that the assay thus meets the requirements for large scale epidemiological studies of FCV infections in cats. However, it has also shown that even the use of RT-PCR on co njunctival swabs alone is insufficient for accurate diagnosis of FCV i nfection in cats with conjunctivitis.