Comparison of clinical features and replication levels following SARS-CoV-infection of aged and juvenile monkeys. (A) Animals were weighed throughout the infection time course and mean values (+/− standard error (SE)) are graphed as the fold change over pre-infection body weight. (B) Body temperature was measured with an implanted subcutaneous temperature microchip transponder. Average daily values (+/− SE) are plotted in degrees Fahrenheit for aged and juvenile monkeys throughout SARS-CoV infection. (C) Viral titers were assessed longitudinally over the infection time course in nasal swabs by plaque-forming assays. The average plaque-forming units (PFU) per ml per nasal swab (+/−SE) are graphed on a log scale. Day 0–5 post infection for aged animals n = 10, day 10 n = 5. Day 0–5 post infection n = 12, for juvenile animals, day 10 n = 6. (D) SARS-CoV replication was also evaluated at 5 days post infection in several respiratory tract tissues including the nose, cranial trachea sample (TrCr), caudal trachea sample (TrCd), and proximal (CdProx), middle (CdMid) and distal (CdDist) portions of the right caudal lung lobe. All tissues were collected in a standardized manner. Bar graphs of the mean (+/−SE) values of plaque-forming units per gram tissue are plotted on a log scale. Aged n = 5, juvenile n = 6 for each tissue. *p < 0.05, **p < 0.01, ***p < 0.0005 by 2-way ANOVA for age or time post infection (d.p.i) as indicated in each graph.