engleski

Isolation of VHSV and IHNV from recent outbreaks on Croatian rainbow trout farms

Croatia is implementing surveillance programme with regard to viral listed diseases and until 2013, only IPNV was present on several salmonid farms. In July 2013, virus causing viral hemorrhagic septicaemia was detected in rainbow trout (Oncorhynchus mykiss) fingerlings from single farm. During 2014, virus was spread to another two farms. Affected fish showed exophthalmia, pale gills, distended abdominal wall with haemorrhages on the skin and in the eyes. On autopsy, haemorrhages on the liver, pyloric caeca, swim bladder, intestine, in dorsal musculature and enlarged spleen were recorded. VHS virus was isolated on cell cultures and identified by ELISA. The diagnosis was confirmed by RT-PCR and partial sequencing of nucleocapsid and glycoprotein genes was performed. The obtained nucleotide sequences were typed as genotype Ia, subtype 2, grouped into subclade Pol II that includes isolates from Poland and Slovenia. In December 2013, virus of infectious haemotopoietic necrosis was detected in samples from newly established rainbow trout farm, submitted as a part of routine monitoring programme. Later, during the 2014, the disease has spread to another three farms. Samples of affected fish showed exophthalmia, pale gills, and sometimes haemorrhage on the skin. Necropsy revealed abundant haemorrhages on the fat tissue, pyloric caeca, peritoneum and intestines and in single specimen on the liver and in dorsal musculature. Examination of organ pools on the cell culture resulted by virus isolation and identification was performed by ELISA. Obtained results were confirmed by RT-PCR and extended mid-G region (615 instead of 303 nucleotids) was sequenced and according to given results we concluded that it is IHNV isolate belonging to M group. Epidemiological investigation included susceptible species from open waters supplying infected farms as well as rivers downstream. All samples from open waters were negative. Further research should be performed to investigate the source of infections.

VHSV; IHNV; Rainbow trout; outbreak; Croatia

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