S-83. An overview of shrimp viral diseases in India

India is one of the leading producers of shrimps in Asia and the world. The shrimp aquaculture industry recorded phenomenal growth in the last two decades. However, in the recent years, shrimp aquaculture is threatened by the epidemics caused by emerging and re-emerging viral pathogens. The main shrimp species cultured in India over the years included Penaeus monodon and Feneropenaeus indicus until 2003 when Litopenaeus vannamei was introduced by some vested farmers. Several farmers have experimented co- culturing of Macrobrachium rosenbergii and Penaeus monodon in low saline waters. The practice of mixing of species and introduction of exotic species could be one of the reasons for emergence of new viruses in India Although theses viruses cause huge economic loss to shrimp industry, the affected animals are safe for human consumption and therefore not as issue with regard to food safety. The major virus of concern has been white spot syndrome virus (WSSV) since its first report in 1995 and causes mass mortalities in shrimp farms. Several other viral agents are also prevalent and cause slow growth such as the monodon baculovirus (MBV), hepatopancreatic parvovirus (HPV), and more recently other viruses such as Laem-Singh virus (LSNV) and infectious hypodermal and hematopoietic necrosis virus (IHHNV) have been detected in a number of samples. The causative agent of loose shell syndrome in shrimps is yet to be confirmed. At present, most of these viruses are detected by PCR which enables screening of large number of samples for multiple viruses in a short time. However, PCR may lead to false negative results if the target region is absent in the genome as in case of Indian WSSV strain. In our study we have found a deletion of 10,970 bp and this has to be borne in mind during design of primers. PCR may sometimes give false positive result as in the case of IHHNV due to the presence of IHHNV-related genome in some strains of the host P. monodon. The recent mass mortalities of shrimps in many farms of India which were negative for WSSV in our study suggest the possible presence of RNA viruses like yellow head virus (YHV), Taura syndrome virus (TSV) and infectious myonecrosis virus (IMNV). The emergence of these new viruses sometimes with more virulence than previously reported could be a result of host switching from the newly introduced shrimp species. Live aquatic animals need to be screened for freedom from pathogens before transboundary movement.