Effect of white spot syndrome virus on the activity of immune-related enzymes in the red claw crayfish (Cherax quadricarinatus)

In this study, we explored the pathogenic effects of white spot syndrome virus (WSSV) and effects of yeast cell wall in the red claw crayfish, Cherax quadricarinatus, by investigating the activity of enzymes related to innate immune function following artificial infection of immunized and non-immunized crayfish. Our results reveal that the activity of four enzymes, phenoloxidase (PO), peroxidase (POD), superoxide dismutase (SOD) and lysozyme (LSZ), increased in the hepatopancreas and antennal gland of C. quadricarinatus 6 - 24 hours after exposure to WSSV. Activity levels of these enzymes decreased rapidly, so that 72 h post-exposure the activity of the enzymes in WSSV-infected crayfish were significantly lower than those of the control individuals (except for LSZ). Interestingly, we found that immunization with yeast cell wall before challenge with WSSV conferred an immune protection rate of 51.86% at 7 days post-infection, demonstrating that yeast cell wall could improve immune-related enzyme activity in the crayfish and enhance the anti-viral defenses of this species. Morphological examination by transmission electron microscopy revealed significant damage in the hepatopancreas and antennal glands of infected crayfish. WSSV infection caused damage to the epithelium of the hepatopancreas and antennas and reduced the number and size of microvilli. In addition, mitochondria morphology changed following infection, with parts of the cristae diminishing leaving large vacuoles. Moreover, the dictyosome morphology changed, the lysosome membranes ruptured, and heterochromatinized nuclei could be seen in cells with ruptured nuclear membranes although no WSSV particles appeared in the hepatopancreas or in the antennal gland.