Health Surveillance of Wild Brown Trout (Salmo trutta fario) in the Czech Republic Revealed a Coexistence of Proliferative Kidney Disease and Piscine Orthoreovirus-3 Infection.

Ľubomír Pojezdal,Ivana Papežíková,Eva Syrová,Miroslava Palíková,Hana Minářová,Veronika Seidlová,Mikolaj Adamek,Dieter Steinhagen,Stanislava Reschová

doi:10.3390/pathogens9080604

Abstract

The population of brown trout (Salmo trutta fario) in continental Europe is on the decline, with infectious diseases confirmed as one of the causative factors. However, no data on the epizootiological situation of wild fish in the Czech Republic are currently available. In this study, brown trout (n = 260) from eight rivers were examined for the presence of viral and parasitical pathogens. Salmonid alphavirus-2, infectious pancreatic necrosis virus, piscine novirhabdovirus (VHSV) and salmonid novirhabdovirus (IHNV) were not detected using PCR. Cell culturing showed no viruses as well, and serological analysis of 110 sera did not detect any specific antibodies against VHSV or IHNV. Fish from two rivers were positive for the presence of piscine orthoreovirus-3 (PRV-3), subtype PRV-3b. However, none of the PRV-3-positive fish showed gross pathologies typically associated with PRV infections. By far the most widespread pathogen was Tetracapsuloides bryosalmonae which was confirmed in each of the examined locations, with a prevalence of up to 65% and 100%, as established by immunohistochemistry and PCR, respectively. Furthermore, up to 43.8% of fish showed signs of proliferative kidney disease caused by T. bryosalmonae, suggesting that this parasite is a main health challenge for brown trout in the Czech Republic.

Highlights

IntroductionRepublic is slowly but steadily increasing, with 1.1 tons of fish produced in 2018 [1]
The number of recirculation and flow-through systems rearing portion-sized salmonids, mostly rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis), in the CzechRepublic is slowly but steadily increasing, with 1.1 tons of fish produced in 2018 [1]
Considering the OIE-listed diseases of viral origin, the Czech Republic is declared free of infectious salmon anemia (ISA), but has a non-defined status considering viral hemorrhagic septicemia (VHS) and infectious hematopoietic necrosis (IHN), with outbreaks of both diseases occurring sporadically throughout the years [4]

Summary

Introduction

Republic is slowly but steadily increasing, with 1.1 tons of fish produced in 2018 [1] Infectious diseases, especially those listed by OIE [2], pose an economic threat to aquaculture either directly, via clinical. The unusually high number of outbreaks of VHS and IHN in the winter of 2013/2014 [5], followed by costly eradication measures, raised the question of the role of wild fish as possible pathogen vectors in the environment of Czech rivers. Piscine novirhabdovirus (formerly viral hemorrhagic septicemia virus, VHSV) remains the greatest problem. This virus was proven to infect wild and feral salmonids in European waters, most notably in direct connection with an active outbreak site in the vicinity [6], but VHSV was identified in asymptomatic animals, such as European river lamprey (Lampetra fluviatilis) in Finland [7], or wild salmonids in Swiss rivers [8]. VHSV was present in multiple wild saltwater species [9,10] and genotype IV of the virus caused massive multi-species mortality events in the North American Great

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