The moribund shrimp challenged with 106, 105 and 104 of 5HP showed clear signs of AHPND histopathology (Fig. 5A–C) similar to those shown in Fig. 2C, E and F. On day 3 after challenge, there was 20% mortality in the group treated with 103 cfu/ml but this was not associated with AHPND pathology. Instead, the moribund shrimp showed collapsed HP tubule epithelia without vacuolization in the E-cell region (Fig. 5D).