Photomicrographs of infected hepatopancreatic tissue of P. vannamei. The adjacent sections of shrimp tissue stained with H&E (column 1) and with the in situ hybridization probe (column 2) showing that hepatopancreatic cells of P. vannamei infected with the microsporidian cannot be easily detected by H&E staining even though extensive infection is revealed by in situ hybridization (dark brown to black staining). (a/b) Low magnification showing that positive reactions are restricted to the medial and proximal tubule epithelial cells of the shrimp hepatopancreas (HP) while the distal E cells are negative. Note that B cells dominate in the infected region. (c/d) Medium high magnification showing pinpoint positive, in situ hybridization reactions in the region of the HP adjacent to the distal E cells region. (e/f) High magnification clearly showing the difficulty in identifying infected cells by H&E staining but their clear revelation by in situ hybridization. (g/h) Very high magnification, emphasizing the features described in (e/f).