Rapid differentiation of Australian, European and American ranaviruses based on variation in major capsid protein gene sequence

Abstract

Epizootic haematopoietic necrosis virus (EHNV), Bohle iridovirus (BIV) and Wamena virus (WV) cause serious diseases in fish, amphibians and snakes, respectively but are restricted to Australasia. European catfish virus (ECV) and sheatfish virus (ESV) have caused epizootics in fish on farms in continental Europe. Currently there are no simple or readily available methods to distinguish these viruses, which are in the Iridoviridae. They are culturally, morphologically and antigenically very similar to Frog Virus 3 (FV3), the type species in Ranavirus in this family and Gutapo virus (GV), another amphibian ranavirus from America. The diseases caused by EHNV, ESV and ECV are so serious that they are internationally notifiable. Tests to distinguish these viruses are desirable to ensure that disease occurrences do not unnecessarily restrict trade in aquaculture products. The gene encoding the major capsid protein from two EHNV isolates from different fish species (Perca fluviatilis and Oncorhynchus mykiss) and one BIV isolate were sequenced and the data and deduced amino acid sequences were compared with those from FV3 and other iridoviruses. The sequences for the two EHNV isolates were identical, confirming suggestions from existing partial MCP sequence that the same type of EHNV infects wild redfin perch and farmed rainbow trout. Differences in restriction endonuclease patterns of specific PCR products were predicted and confirmed between EHNV, BIV, and WV and provided a basis for rapid differentiation of these viruses from each other and from ESV/ECV and FV3/GV. These simple and rapid tests to distinguish important ranaviruses from the regions of Europe, Australia and America will help regulatory authorities assess the need for disease control responses in the event of occurrence of ranavirus infection in aquaculture species.