Mean Plasma and Milk Viral Loads in Early, Late and Non-Transmitting Macaques. Viral RNA copies measured by real-time RT-PCR in cell-free fraction of milk samples obtained from lactating macaques. Samples that could be amplified by PCR, but had values calculated as having ≤50 copies RNA/ml (amplifiable but not quantifiable) were indicated as having 50 copies. Samples from which viral RNA could not be amplified were indicated as having 1 copy. Early transmitters are shown in yellow, late transmitters in red and non-transmitters in blue.