Visualization of minute centers of viral infection in unfixed cell cultures by an enzyme-linked antibody assay

Enzyme-linked antibody was used to treat unfixed herpesvirus-infected human fetal lung cell cultures in a mode which permitted the visualizing of local sites of infection. Foci containing as few as 20 herpesvirus-infected cells produced sufficient viral mass to be easily detectable by this method. 'Clouds' or 'plumes' of colored reaction product diffused into the substrate overlay, accumulated above and around each focus of infection and allowed quantitation of the number of foci in a culture. The number of minute centers of viral infection determined by the enzyme-linked antibody method corresponded almost exactly with values obtained by fluorescence microscopy. Quantitation of herpes simplex infectivity by focus assay was possible within only 17 h after culture inoculation, well before cytopathic effects were visible macroscopically. The technique was also applied to demonstrate measles and mumpsvirus plaques (infectious centers) in Vero cell cultures.