Course of infection in the four foals # 9, # 10, # 17 and # 19 from parturition until the ages of approximately 13 months. Serum samples from the first three sampling time points (at parturition and at the ages of 3 and 6 months are derived from a previous study (marked with a grey background) . Until the ages of 12–13 months these foals were further monitored within this follow-up study and serum was taken at three additional time points. All serum samples were analyzed for the presence of anti-NPHV NS3 antibodies (ab) (grey bullet) and NPHV RNA (black square) by LIPS and qRT-PCR, respectively. The cut-off limit for the LIPS was determined by the mean value of wells containing only buffer A, the RUC-NS3 fusion protein and A/G beads plus three standard deviations and is illustrated as dashed line. In the lower panels, liver specific parameters (GLDH, GGT and AST) are shown for each foal at the three follow-up time points as unfilled symbols, with the following reference ranges set by the laboratory: GLDH < 6 U/L, GGT < 20 U/L and AST < 170 U/L. (A) Foal # 9, (B) foal # 10, (C) foal # 17 and (D) foal # 19.