Abstract:Grass carp haemorrhage is an epidemic disease, which is caused by grass carp reovirus (GCRV). Grass carp fingerlings and yearlings are vulnerable to GCRV. A virulent reovirus, tentatively named GCRV-AH528, was isolated from a diseased grass carp exhibiting typical hemorrhage symptoms in Hefei, Anhui Province. Intraperitoneal injection with the virus suspension led to hemorrhage similar to the observed clinical symptoms of blackened dorsum and hemorrhage around the mouth cavity, gill, intestine, belly, and base of the fin ray. The GCRV-AH528 genome contained 11 double-stranded RNA segments ranging from 1027 to 3925 bp, and its average content of AT and GC was 50.2% and 49.8%, respectively. Compared with registered GCRV Ⅱ strains, the GCRV-AH528 L1 segment had lost three continuous nucleotides (TAT) at nt 701~702, leading to the loss of a tyrosine, and the M4 segment mutated two ORFs encoding two non-structural proteins (NS9 and NS69). All segments had 6 bp-conserved terminal nucleotides 5'-GUAAU/CUUU/GCAUC-3'. Except for the L1 and M6 segments, the two ends in the coding region of the other nine segments existed at 5~9 bp short specific inverted complementary sequences. GCRV-AH528 showed 37.1%~98.1% nucleotide and 24.3%~98.3% AA sequence identities with other reovirus. A phylogenetic tree based on VP1 protein revealed that GCRV-AH528 clustered with members of the genus Aquareovirus and was far from GCRV-873. These results indicated that the GCRV-AH528 isolate was a new GCRV Ⅱ type virulent strain.
