Prevalence of piscine myocarditis virus (PMCV) in marine fish species

Cardiomyopathy syndrome (CMS) is an inflammatory disease of the heart primarily affecting farmed Atlantic salmon, Salmo salar L. (Ferguson, Poppe & Speare 1990). The disease mainly appears in fish 12–15 months after transfer to sea water, and pathological signs include inflammation of the endocardium and spongiosum of the atrium and ventricle. Highest mortality rates are seen in fish weighing 2–5 kg, and the cause of death is generally rupturing of the atrium or sinus venosus. The disease has been reported from locations all along the Norwegian coastline since the 1980s (Amin & Trasti 1988) and has also been observed in Scotland (Rodger & Turnbull 2000), the Faroe Islands (Sande & Poppe 1995) and Canada (Brocklebank & Raverty 2002). CMS causes substantial financial losses for the fish farming industry (Brun, Poppe, Skrudland & Jarp 2003), and CMS-like lesions have also been observed in wild Atlantic salmon (Poppe & Seierstad 2003). The causative agent is most likely a naked, double-stranded RNA virus related to the Totiviridae group, provisionally named piscine myocarditis virus (PMCV) (Lovoll, Wiik-Nielsen, Grove, WiikNielsen, Kristoffersen, Faller et al. 2010; Haugland, Mikalsen, Nilsen, Lindmo, Thu, Eliassen et al. 2011), and thus far, the virus has been found exclusively in farmed Atlantic salmon sampled from pens with CMS. Using a PMCV-specific real-time PCR assay (Lovoll et al. 2010), we have screened for the presence of PMCV in more than 30 species of marine fish (Table 1) sampled off the central, western coastline of Norway from Trondheim to the Varanger fjord. The set of samples was a representative subset of the catch from a single trawling expedition. Sampling was performed and financed by the project Viral haemorrhagic septicaemia virus (VHSV) in wild and farmed fish in Norway (NFR-190245), and more details on the sampling will be published later along with other results from this project. Organ samples of spleen, kidney and brain were pooled and directly frozen in transport medium (Leibovitz culture medium supplemented with 4 mm l-glutamine and 100 ng mL gentamicin; all from Sigma-Aldrich). Each pool consisted of material from 1 to 5 individuals of the same fish species sampled at the same time and place. For some of the samples included in the pools, kidney tissue from individual fish was also stored on RNAlater (Qiagen AB). Nucleic acids from the organ pools were extracted from 100 uL of tissue homogenate using the NucliSENS easyMAG nucleic acid extraction system (bioMerieux, Inc.) according to the manufacturer s recommendations. RNA from individual fish kidneys was extracted using an RNeasy Mini kit (Qiagen AB). A total of 342 pools (1501 individuals) representing 32 species were screened. The majority of the samples were negative, but 11 of 38 pools from Argentina silus gave a positive PCR result (Table 1). Journal of Fish Diseases 2011, 34, 955–957 doi:10.1111/j.1365-2761.2011.01315.x