EN
The kinetics of replication of equine influenza A1 and A2 viruses in different systems e.g. chicken embryos, Vero, MDCK and MDBK cell lines was evaluated. The strains A/Equi/1/Praque 56 and A/Equi/2/Kentucky 81 were used. A dose of 0.2 ml of influenza A1 and A2 viruses with the haemagglutinin titre (HA) 256 diluted to 10⁻³ and 10⁻⁴ respectively, was found out to be optimal for inoculation of chicken embryos. The highest HA titre for viruses A1 and A2 were noticed after a 72 hours of incubation post inoculation. The ID₅₀ and LD₅₀ titres differed by more than 2 log in case of A1 virus. Both equine influenza viruses replicated in Vero, MDCK and MDBK cells; however, MDCK cells have revealed the highest sensitivity to infection. Low haemagglutinin titres found in the medium from infected cell lines have suggested that this is rather poor source of virus antigens for vaccine production.