The multicycle growth kinetics of the viruses was evaluated in DF1 cells. Duplicate wells of six-well plates were infected with each APMV at an MOI of 0.01 PFU/cell. After 1 h of adsorption, the cells were washed and then covered with DMEM containing 2% FBS at 37uC in 5% CO 2 . APMV-1 LaSota, APMV-3, -8, and -9 were supplemented with protease, as described above. Supernatants were collected and replaced with an equal volume of fresh medium at 12-h intervals until 72 h post-infection (hpi). Virus titers in the collected supernatants were quantified in DF1 cells or Vero cells by limiting dilution and immunostaining with N-specific antibodies [29] [30] . Virus titers were expressed as 50% tissue culture infectious dose (TCID 50 /ml) by the end-point method of Reed and Muench [31] .