Detection of YFV antigens in the liver biopsy collected at the 93rd day post-onset of first symptoms of yellow fever. (A) Histopathology of the hepatic biopsy. Portal and lobular mononuclear infiltrate, predominantly in zones 2 and 3 of the hepatic acini, and hepatocyte vacuolar degeneration are observed (H&E, 40X); (B) Immunohistochemistry of the hepatic biopsy. The yellow fever antigen was detected by immunohistochemistry in the cytoplasm of hepatocytes (brown areas) (DAB [3, 3’-diaminobenzidine], using a YFV-specific monoclonal antibody; 40X). YFV-specific monoclonal antibody was kindly provided by Dr. Pedro Fernando da Costa Vasconcelos, from Evandro Chagas Institute, Pará, Brazil).