Detection of low-virulent classical swine fever virus in blood of experimentally infected animals: comparison of different methods.

The effectiveness of virus isolation, commercial antigen enzyme-linked immunosorbent assay (ELISA), reverse transcriptase-polymerase chain reaction (RT-PCR), and flow cytometry in detection of a low-virulent classical swine fever virus (CSFV) in blood in the early period of infection was evaluated. Domestic pigs at the age of 6-8 weeks and young wild boars were inoculated with a low-virulent field isolate of CSFV originating from a wild boar. This virus induced serious clinical reaction in only one pig which was naturally infected with Pasteurella multocida. Nine of 13 infected domestic pigs showed viremia. All infected weanling pigs were found viraemic by virus isolation on day 6 post infection (p.i.) but virus-free by RT-PCR. The flow cytometry was apparently not as sensitive as the virus isolation. Two young wild boars infected with the virus were viremic only for the first 2 days p.i. Virus isolation and RT-PCR were of similar sensitivity. Three different commercial antigen ELISAs used were not able to detect viral antigen in any animal.