Successful scans were obtained from at least two animals at each time-point, details of completed scans are given in Fig.4A. It was not always possible to complete an MRI scan on each mouse at every time-point. Failures were encountered due to the technically demanding nature of the technique. In some instances cannulation of the tail vein proved impossible or the cannula became dislodged, while on other occasions the indwelling cannula became obstructed, most likely due to the presence of a blood clot, and prevented injection of the contrast agent.Fig. 4Assessing BBB dysfunction. A. Summary table indicating successful scans (✓) performed at each stage after infection. B. The degree of BBB dysfunction was determined by calculating the percentage signal change present in the brain following CE-MRI. Significant levels of barrier impairment were detected on day 14 post-infection compared with uninfected animals or those scanned at 7 days post-infection. A stepwise increase in BBB dysfunction was detected at days 21 and 28 post-infection. Dots represent the group mean (n = 2–4 in each group), bars represent one standard error of the mean. The means of groups that do not share a letter are significantly different (p < 0.05) from each other.