Comparison of LASV NP antigen detection by ELISA versus RNA quantification by qPCR. RNA was prepared from serum samples as outlined in materials and methods. RT-PCR followed by qPCR directed against the GPC gene was performed on days 7-18. A 1:6 dilution series of Josiah strain seed stock was used as a standard to calculate the LASV RNA copy number per milliliter of serum. PCR data were plotted on the second Y axis (LASV RNA copies/mL). Error-bars represent the SEM of two independent experiments. NP Ag ELISA data was plotted on the first Y axis (A450) for trend comparison. Trend lines for NP Ag ELISA (power) and qPCR (exponential), and associated R2 values are indicated. The limit of detection for antigen by NP Ag ELISA was day 9 (blue arrow), and day 11 for qPCR (red arrow).