Nonspecific antiviral substances in human milk active against arbovirus and murine leukemia virus.

Forty-three individual human milk samples obtained 2 weeks to 17 months postpartum were divided into five large pools. Theseplus three large individual human milk samples obtained 2 and 5 months postpartum were tested for antiviral activity against Japanese B encephalitis virus, Friend leukemia virus, and Rauscher leukemia virus. All milk samples had a high degree of antiviral activity against the three viruses. The bulk, ifnot all, ofthe antiviral activity appeared to be in the cream fraction and was remarkably heat stable. Heating the milk to temperatures up to 100°for 30 mm had no effect upon its ability to destroy the infectivity of Japanese B encephalitis virus or inhibit the ability of Friend leukemia virus to induce splenomegaly.