Foot-and-mouth disease virus: selection by homogenized calf kidney adsorption and cell culture passage.

Foot-and-mouth disease virus was passaged 20 times by alternately adsorbing the virus with homogenized calf kidney and propagating the adsorption-resistant fraction of virus in cell cultures. Passage of the virus was accompanied by a marked decrease in pathogenicity for 35-day-old mice and a reduction in its ability to adsorb to homogenized kidney from such mice. Adsorption by homogenized calf kidney and infant mouse kidney also decreased with passage, but pathogenicity for cattle and infant mice remained high. The passaged virus did not seem to change antigenically. When the 20th-passage virus was serially passaged 10 times in cell cultures, no reversion in pathogenicity for 35-day-old mice was observed.