Verification of positive controls for testing adventitious virus agents in Japanese encephalitis vaccine

Objective To verify appropriate positive controls for testing adventitious virus agents in Japanese encephalitis vaccine. Methods Japanese encephalitis virus, diluted to different concentrations, was incubated with 3 different types of cells for 2-3 d. Cytopathic effect (CPE) was observed at the end of incubation and the concentration of virus showing the most representative CPE was chosen as positive control. Phytohemagglutinin was diluted to different concentrations with 0.5% chicken and guinea pig red blood cell suspension, and hemadsorption tests were conducted after 0.5 h incubation at either 2-8 ℃ or 20-25 ℃. The concentration of phytohemagglutinin that showed the most representative hemadsorption was chosen as positive control. Results The Japanese encephalitis virus concentration of 3-4 lg plaque-forming unit/ml caused 20%-50% CPE, and the phytohemagglutinin concentration of 30-40 mg/L resulted in 20%-50% adsorption hemagglutination. Conclusion Japanese encephalitis virus and phytohemagglutinin at certain concentrations can be used as positive controls for testing adventitious virus agents in Japanese encephalitis vaccine. Key words: Japanese encephalitis vaccines; Microbial consortia; Positive control; Phytohemagglutinins