A synthetic antibacterial peptide from Mytilus galloprovincialis reduces mortality due to white spot syndrome virus in palaemonid shrimp J-W Dupuy, J-R Bonami and Ph Roch Pathoge `nes et Immunite ´, DRIM, Universite ´ de Montpellier 2, Montpellier, France Abstract White spot syndrome virus (WSSV) isolated from Penaeus monodon was found to be highly infective for the western Mediterranean shrimp, Palaemon sp. Using polymerase chain reaction (PCR), it was demonstrated that such shrimp are not naturally carriers of WSSV. Following challenge with virus, mortality reached 100% 3.5–4 days after injection at 22 °C. Incubation of infected shrimp at 10 °C totally suppressed the mortality which rapidly developed when shrimp were returned to 18 or 22 °C. Preincubation of WSSV with mature syn- thetic mytilin significantly reduced shrimp mortal- ity with a 50% efficient dose of about 5 lm. Survival of shrimp was not due to the development of an active mechanism of defence as re-injection of WSSV produced the same mortality pattern. Mor- tality was probably due to WSSV replication as dot blot failed to detect viral DNA in the injection sample but was positive 1 day post-injection. Pro- tection by mytilin was by interaction at the virus level, preventing replication as no WSSV nucleic acid was detected by PCR even after 7 days in shrimp injected with WSSV preincubated with 10 or 50 lm mytilin. Keywords: antimicrobial peptides, Mytilus, shrimp, viral protection, white spot syndrome virus. Introduction White spot syndrome virus (WSSV) causes major disease outbreaks in cultured penaeid shrimp. The disease develops rapidly and cumulative mortality usually reaches 100% within 3–10 days (Lightner 1996; Flegel 1997). The virus was first discovered in eastern Asia (Cai, Huang, Wang, Song, Sun, Yu, Zhang & Yang 1995) and intensive cultiva- tion, inadequate sanitation and worldwide uncon- trolled movements have quickly spread the disease to nearly all shrimp-farming areas (Rosenberry 2000). Moreover, WSSV has also been detected in other freshwater and marine crustaceans (Lo, Ho, Peng, Chen, Hsu, Chiu, Chang, Liu, Su, Wang & Kou 1996). In European crustaceans, experi- mental infection resulted in similar clinical signs and mortalities (Corbel, Zuprizal, Shi, Huang, Sumartono, Arcier & Bonami 2001). WSSV is thus not only a major threat to the shrimp industry but also to wider marine crustacean populations. Antivirus immune defence is mediated by multifunctional cytokines collectively named inter- feron (Isaacs & Lindenmann 1957; Janeway, Travers, Walport & Shlomchik 2001). Despite their ancient divergence, estimated at 400 million years ago (Weissmann & Weber 1986), no interferon-like molecule has been reported in invertebrates, either at the protein or genome level. The innate immune system of invertebrates is characterized by a diversity of antimicrobial pep- tides, cationic molecules of 4–10 kDa. Most studies have focussed on their antibacterial, antifungal (Bulet, He ´tru, Dimarcq & Hoffmann 1999) or antiparasitic (Boulanger, Munks, Hamilton, Vovel- le, Brun, Lehane & Bulet 2002) properties. Journal of Fish Diseases 2004, 27, 57–64 Correspondence Philippe Roch, Universite´ de Montpellier 2, case courrier 080, Place Euge`ne Bataillon, F-34095 Montpellier Cedex 5, France (e-mail: proch@univ-montp2.fr) 57 Ó 2004 Blackwell Publishing Ltd