Foot and mouth disease virus. Properties of a clone selected by terminal dilution technique from the original population.

Using the terminal dilution technique, a cloned virus was selected in a tissue culture systems from a heterogenous population of the original virus. The different markers studied differentiated the cloned virus from the original virus on the basis of its following characters: 1. ability to grow more efficiently at 29 than at 37 degrees C. 2. unstability of its capsid as seen by: a. high degree of sensitivity to heating at 50 degrees C for 10 min of exposure to pH 6.4 for 10 min. b. more inactivation by overnight exposure to 37 and 4 degrees C. 3. late pathogenicity in the suckling mice. The practical usefulness of a simple technique of the selection of viral clones and the possibilities of such clones to be used in the liver (modified) vaccine are discussed.