Viral replication in excised fin tissues (VREFT) corresponds with prior exposure of Pacific herring, Clupea pallasii (Valenciennes), to viral haemorrhagic septicaemia virus (VHSV)

Abstract

Procedures for a viral replication in excised fin tissue (VREFT) assay were adapted to Pacific herring, Clupea pallasii, and optimized both to reduce processing time and to provide the greatest resolution between naïve herring and those previously exposed to viral haemorrhagic septicaemia virus (VHSV), Genogroup IVa. The optimized procedures included removal of the left pectoral fin from a euthanized fish, inoculation of the fin with >10(5) plaque-forming units (PFU) mL(-1) VHSV for 1 h, rinsing the fin in fresh medium six times to remove unadsorbed virions, incubation of the fin in fresh medium for 4 days and enumeration of the viral titre in a sample of the incubation medium by plaque assay. The optimized VREFT assay was effective at identifying the prior exposure history of laboratory-reared Pacific herring to VHSV. The geometric mean VREFT value was significantly greater (P < 0.01) among naïve herring (1.2 × 10(3) PFU mL(-1) ) than among groups that survived exposure to VHSV (1.0-2.9 × 10(2) PFU mL(-1) ); additionally, the proportion of cultures with no detectable virus was significantly greater (P = 0.0002) among fish that survived exposure to VHSV (39-47%) than among naïve fish (3.3%). The optimized VREFT assay demonstrates promise for identifying VHSV exposure history and forecasting disease potential in populations of wild Pacific herring.

Fin and gill biopsies are effective nonlethal samples for detection of Viral hemorrhagic septicemia virus genotype IVb

“…9,23 Excised fin tissues of herring (Clupea pallasii pallasii; Valenciennes, 1847) can replicate VHSV-IVa. 14 Genotype I of VHSV infects gill tissue in rainbow trout, and the ability of the virus to translocate across the gill epithelium correlates with in vivo virulence. 6 Results of the current study strongly suggest that fin and gill biopsies can be used as an effective nonlethal sample type for VHSV-IVb testing.…”

Passive Immunization of Pacific Herring against Viral Hemorrhagic Septicemia

“…In Pacific herring, the low sensitivity of the plaque neutralization assay makes it ineffective at identifying a protective level of immunity among individual fish; however, the exposure history of a population may be ascertained by collecting plasma from wild individuals and conducting passive immunization studies (as described here). Similarly, a technique involving viral replication in fin explant tissues was effective at determining the VHSV exposure history of Pacific herring: fin explants from VHS survivors produced lower viral titers after in vitro exposure than did fin explants from naïve individuals (Grady et al 2011). Although the efficacies of both the fin explant and passive immunization techniques were demonstrated under laboratory conditions, issues of scale and cost would probably preclude application of either technique as a viable population screening tool.…”