Myxovirus replication in chicken embryos can be suppressed by aprotinin due to the blockage of viral glycoprotein cleavage.

Injection of the protease inhibitor, aprotinin, into the allantoic cavity of embryonated eggs infected at low m.o.i. with different influenza viruses and paramyxoviruses markedly reduced multiplication by at least 100-fold. Under these conditions, most viral particles produced were non-infectious and contained uncleaved glycoproteins, presumably resulting from aprotinin suppression of protease activity.