Figure 3. Pathology and viral loads in selected tissue samples.

(a) Gross pathology of lungs from IFN-α2b– and ribavirin–treated (left) and untreated (middle) MERS-CoV–infected rhesus macaques 72 h after inoculation. The percentage area showing gross pathology is indicated on the right. Six lung lobes per animal (dorsal and ventral) from three animals per group were scored. (b) The mean viral load determined by qRT-PCR from individual tissues collected at necropsy. The mean viral load of all lung lobes combined is indicated in the inset. Log TCID₅₀ eq/g, log TCID₅₀ equivalents per gram tissue; one sample per tissue per animal from three animals per group were analyzed. (c,d) Lung tissue collected at necropsy stained with H&E. Pulmonary arterioles appear normal in treated animals (RM2) (c, left). Treated RM2 shows mild acute bronchointerstitial pneumonia demonstrated by multifocal accumulations of inflammatory cells centered on terminal bronchioles (c, middle). Higher magnification of the boxed region showing thickening of the alveolar septae by small numbers of neutrophils, macrophages, fibrin and edema (asterisk) (c, right). Pulmonary arterioles are bounded by moderate numbers of lymphocytes indicative of perivasculitis in untreated animals (d, left). Larger numbers of inflammatory cells and fibrin also extend into alveolar spaces. Untreated RM4 shows marked coalescing bronchointerstitial pneumonia with abundant alveolar fibrin and edema (d, middle). Higher magnification of untreated RM4 showing airways filled with organizing fibrin (arrow) and moderate numbers of viable and degenerate neutrophils and macrophages (d, right). (e) Percentage of neutrophils in lung sections stained with myeloperoxidase. Two sections per lobe and six lobes per animal from three animals per group were analyzed. All values are mean ± s.d. (t-test, ^*P < 0.05, ^**P < 0.01).