Inhibition of herpes simplex virus strains isolated from herpetic keratitis by polyinosinic acid polycytidylic acid

Fifty strains of herpes simplex virus, isolated from patients with herpetic keratitis, were examined in vitro for susceptibility to polyinosinic acid-polycytidylic acid [poly (I:C)] in the presence of a constant concentration of diethylaminoethyl-dextran. The minimal inhibitory concentration of poly (I:C) for 44 of these strains ranged from 0.0001 to 0.1 μg/ml; for the remaining six strains, the minimal inhibitory concentration stood at 1 to 2 μg/ml. Fifteen isolates from primary infections were more susceptible to poly (I:C) than 35 isolates from recurrent infections. Isolates acquired at different points of a given clinical episode showed similar susceptibilities to poly (I:C). In two patients, isolates from consecutive recurrences of infection exhibited reduced susceptibilities. The implications of the above observations for the therapeutic use of poly (I:C) are discussed.