Differential and Specific Inhibition of ECHO Viruses by Plant Extracts. ∗

Abstract

Summary

1) Comparison of antiviral activity of several plant extracts against several ECHO viruses revealed that M2, prepared from a strain of Calvatia gigantea significantly inhibited only ECHO 4 and 11; while M4, a different preparation from the same strain, inhibited only ECHO 7 and 8; and M14, from a species of Cattleya, inhibited ECHO 2. The effectiveness of M2 in vitro was greatest when the cells were pretreated and when the virus inocula did not exceed 100 TCID₅₀. 2) Specificity of the antiviral action of M2 was demonstrated by inhibition of one M2-susceptible virus followed in the same culture by growth of a second M2-nonsusceptible virus. Inhibition continued, however, if the cultures were reinoculated with a second M2-susceptible virus. 3) Activity of M2 was demonstrated in vivo by its ability to suppress the antigenicity of an M2-susceptible virus. 4) The results demonstrate strikingly the capacity of the materials to prevent infection of susceptible cells by specific viruses although the cells retain their physiologic competence to support growth of other viruses and the virus is not directly affected by the inhibitory material. Obviously the effect must be directed to modification of reactions essential to viral development but not injurious to functional integrity of the cell.