Serological Survey of Epizootic Fish Viral Diseases in Some Rearing Rainbow Trout Farms by Enzyme-Linked Immunoabsorbent Assay (Elisa) in Iran

Immunological methods (e.g. FAT, IHC, ELISA) enable the rapid specific detection of fish pathogens. Enzyme-Linked Immunosorbent Assay (ELISA) method can also be used in serology (detection of pathogen-specific antibodies in the host fishes) as a means of disease surveillance programs in aquaculture. IHN, IPN and VHS are serious viral diseases in rainbow trout farms. In the present study, ELISA as a serologic method was carried out for the detection of the causative pathogens and confirmation of virology examination. Fifty-three serums of rainbow trout broodstocks (29 female and 24 male) were examined for detection of antibodies against IHNV, IPNV and VHSV that were collected from 13 hatchery and rearing farms in three provinces in Iran (March 2002 until November 2003). Also in order to confirm the results of virology examination two samples that had revealed CPE in cell lines were chosen. Finally, 44 serum specimens plus 24 negative control samples (8 for each suspect virus: IHNV, IPNV and VHSV) were selected for ELISA examination. Blood samples were taken from a caudal vein and Serum was separated after centrifuging, nine samples were omitted for some technical problems such as hemolysis, finally, serum specimens were transferred in sturdy, leak-proof plastic vials and stored at -20ºC freezers. Then was used of ELISA examination and all Optical Density (O.D) were obtained. All (O.D)s more than Cut-off Point were considered as positive samples. So regarding ELISA findings and disease incidence percentage (Number of all positive case standing above Cut-off point divided to all examined suspected samples), IHNV had more percentage of disease in ELISA test with 23.25% in comparison with other relevant viral diseases i.e. VHSV with 14.29% and IPNV with 7.31 %. These findings and disease incidence percentage show that IHN could be one of the most important viral diseases in Iran. In fact, serology findings in ELISA could be supported strongly from virology conclusion and confirmed Rhabdovirus-like particles (that was observed previously in virology examination) as the main causative agent in the occurrence of IHN in the hatchery and rearing Rainbow trout farms in Iran. Rapid and sensitive diagnosis methods of fish viral infectious diseases are very critical if dissemination of the viruses causing these diseases is to be controlled because no effective vaccines or treatment currently exist for their control and prevention in the country