Antiviral Substances in Plants of the Mint Family (Labiatae). I. Tannin of Melissa officinalis.

Summary Tannin-containing fractions from aqueous extracts of Melissa officinalis were prepared by gelatin precipitation, hide-powder adsorption, and lead acetate precipitation and it was found that the tannin recovered from these preparations was the hemagglutination inhibitor for Newcastle disease virus. Tannin prepared by gelatin precipitation showed antiviral activity in tests in eggs and in plaque-inhibition tests with Newcastle disease virus and hemagglutination tests with mumps virus. Aqueous extracts of the melissa plant blocked hemadsorption by parainfluenza viruses 1, 2, and 3. The tannin of this plant appears to have an affinity for myxoviruses of subgroup 2 but has no effect on influenza A and B viruses in hemagglutination and hemadsorption tests. The tannin is not primarily virucidal for Newcastle disease virus; its effect is a neutralization which can be reversed by dilution or by addition of gelatin.