GPT and infection: Biomarkers have been most thoroughly studied in the A/Ncr and C57BL/6 mice following an IN infection and include: 1) AST (alanine aminotransferase) and ALT (aspartate aminotransferase) which give an indication of liver damage; 2) ECTV DNA can be detected and quantified with PCR (polymerase chain reaction) from whole blood as early as 4 days p.i.; and 3) Weight change provides a good trailing indicator of morbidity (see Table 2) [40].