Effects of the sulfated polysaccharides dextran sulfate and heparin on shrimp immunity and infection by white spot syndrome virus and Vibrio parahaemolyticus

Abstract

White spot syndrome virus (WSSV) and Vibrio parahaemolyticus are major pathogens of the economically important shrimp, Litopenaeus vannamei, causing white spot syndrome and hepatopancreatic necrosis disease (AHPND), respectively. In animals, sulfated glycosaminoglycans, particularly heparan sulfate, are key regulators controlling cell communication and infectivity of pathogens. We have tested the hypothesis that dextran sulfate and heparin would afford some protection against white spot syndrome and AHPND. Injection of dextran sulfate (1 % w/v), and heparin (0.3 % w/v) were not toxic, and encouragingly, co-injection of these with WSSV provided some delay in mortality to the shrimp. We then used shrimp feed supplemented with 1 % (w/w) dextran sulfate and 0.1 % (w/w) heparin for 14 days prior to infection by cohabitation with WSSV-infected shrimp or addition of V. parahaemolyticus to tank water. In the absence of pathogen, these feeds altered the shrimp immune response: enhancing PO activity and the expression of Lvpo1, Lvpo2, Lvlyso2, Lvpen3, Lvalf1, and Lvalf2, though no effect on the shrimp microbiome was observed. These activities of dextran sulfate and heparin differed, likely due to their different patterns of sulfated sugars. In the infection challenge, these feeds delayed mortality of the shrimp in WSSV infection, but not with V. parahaemolyticus. The data demonstrate that sulfated polysaccharides can modulate shrimp immunity and prolong the survival of WSSV-infected shrimp. Given there are many natural sulfated polysaccharides of diverse structure, there may be more effective and cheaper food supplements which would go some way to resolving WSSV infections in aquaculture.