Immunohistochemistry and pathology of multiple Great Lakes fish from mortality events associated with viral hemorrhagic septicemia virus type IVb

Abstract

A novel viral hemorrhagic septicemia virus (VHSV) (genotype IVb) has been isolated from mortality events in a range of wild freshwater fish from the Great Lakes since 2005. In 2005 and 2006, numerous new freshwater host species (~90 fish from 12 different species) were confirmed to have VHSV by cell culture and reverse transcriptase polymerase chain reaction. A prominent feature observed in infected fish were the petechial and ecchymotic haemorrhages on the body surface and in visceral organs, as well as serosanguinous ascites; however, many fish had few and subtle, gross lesions. Histologically, virtually all fish had a vasculitis and multifocal necrosis of numerous tissues. Excellent correlation was found between the presence of VHSV IVb antigen detected by immunohistochemistry and the pathological changes noted by light microscopy. Intact and degenerate leukocytes, including cells resembling lymphocytes and macrophages, also had cytoplasmic viral antigen. By contrast, renal tubules and gonadal tissues (ovary and testis), were strongly immunopositive for VHSV IVb, but no lesions were noted.

Screening for Viral Hemorrhagic Septicemia Virus in Marine Fish along the Norwegian Coastal Line

“…rRT-PCR testing indicates that the highest amount of VHSV RNA was found in the heart and the highest prevalence were detected in gills. Heart samples are suitable for detecting VHSV in various fish species as it is an important target organ for VHSV [18], [42]–[45]. According to OIE (Commissions decision 2001/183) heart and/or brain samples should be included in screenings surveys.…”

“…It is still debated to what extent VHSV play a role in stock and population variations of Pacific herring Clupea pallasii ([13], reviewed in [14]). Over the past decade VHSV genotype IVb has become an emerging problem in the Great Lakes region in North America causing high mortality in several wild fish species [13], [15]–[18]. Subtype IVc has been isolated from brackish fishes during mortality events in Atlantic coastal regions of North America including mummichog Fundulus heteroclitus , stickleback Gasterosteidae, striped bass Morone saxatilis and brown trout Salmo trutta [12], [19].…”

Immunity to Fish Rhabdoviruses

“…Several of these viruses (IHNV, VHSV, and SVCV) are reportable to The World Organization for Animal Health (OIE). IHN primarily occurs in salmon and trout [4] and SVC primarily afflicts cyprinid fishes [5], while the list of VHS susceptible hosts continues to grow [6]. These viruses cause significant mortality and morbidity in both wild and cultured fish [1].…”

Susceptibility of goldsinny wrasse, Ctenolabrus rupestris L. (Labridae), to viral haemorrhagic septicaemia virus (VHSV) genotype III: Experimental challenge and pathology

“…Swelling of these cells can lead to a narrowing of the capillary network and a consequent reduction of blood flow (Mazzoni et al, 1995) and changes in the interaction with the adjacent cardiomyocytes which plays an important role in heart development and function (Brutsaert, 2003). Similar histopathological changes in heart, including a moderate myocarditis, were observed in freshwater drum (Aplodinotus grunniens) infected with VHSV IVb (Al-Hussinee et al, 2011) and endothelial dysfunction is also a known hallmark of other systematic vascular diseases of salmonids including ISAV (Aamelfot et al, 2015). The extent to which molecular or cellular mechanisms drive the potential of heart failure in wrasse is unknown and is worthy of further investigations.…”