Persistent measles virus infection in a calf kidney cell line. Note II. Study of some biological markers of the measles virus isolated from a selected chronically infected cell line.

The biological characteristics of a measles virus strain (Co-69/pi) isolated from a selected chronically infected calf kidney cell line (K-2) are studied in comparison with those of thw wild parental CO-69 and of the attenuated Schwarz measles virus strain. Co-69/pi is a variant of the parental Co-69 virus and has characteristics of an attenuated strain. Some of the characteristics acquired by the Co-69/pi strain (cytopathogenicity, size of plaques) proved to be stable in the course of passages on a simian substrate. The mechanism having led to the appearance of this variant in the chronically infected cell line are discussed.