Effects of white spot syndrome virus infection and role of immune polysaccharides of juvenile Cherax quadricarinatus

In this study, we infected juvenile red claw crayfish, Cherax quadricarinatus, with white spot syndrome virus (WSSV). We used biochemistry, transmission electron microscopy (TEM) and molecular biology methods to compare the enzymatic activities of lysozyme (LSZ), phenoloxidase (PO), peroxidase (POD), and superoxide dismutase (SOD), and morphological and CqHC gene expression changes in gills and hemolymph of juvenile C. quadricarinatus. Biochemical studies showed that, in comparison with the control group, the activities of LSZ, PO, POD and SOD in group I (injected with 50 μl WSSV) were significantly decreased after 72 h (P < 0.01). Four enzymatic activities in group III (injected with 50 μl immune polysaccharides followed by 50 μl WSSV after 48 h) were all greater than in group I (P < 0.05). The morphological study in the gills and hemolymph of C. quadricarinatus showed that many virus particles appeared in gill tissue and the mitochondrial cristae disappeared. Hemocytes had heterochromatin in the nucleus, and there was an increase in large granule cells with abnormal volumes. Our results indicate that WSSV infection can damage the ultrastructure of the gills and hemolymph in juvenile C. quadricarinatus. Real-time polymerase chain reaction showed that CqHC gene had the highest expression level in the hepatopancreas, and expression of the HC gene sharply declined as infection progressed (P < 0.01). The expression level of HC gene in group III was significantly higher than in group I except at 6 h (P < 0.05). These observations show that immune polysaccharides can promote the resistance of juvenile prawns to WSSV infection.