Evaluation of lethal and non‐lethal sampling methods for the detection of white sturgeon iridovirus infection in white sturgeon, Acipenser transmontanus (Richardson)

Abstract

Pectoral fin tissue of white sturgeon was investigated as a potential non-lethal sample source for the detection of white sturgeon iridovirus (WSIV) infection. Histopathology and polymerase chain reaction (PCR) results using fin tissue were compared with the standard lethal histopathology sampling method that utilizes head tissue. Tissues for each of the three sampling methods were collected weekly for 8 weeks from individual sturgeon undergoing an experimental cohabitation challenge with fish infected with the Abernathy isolate of WSIV. Non-lethal fin histopathological evaluation did not reveal infection during the first 3 weeks of sampling, while non-lethal PCR and the lethal method were variable. However, all three sampling methods were equally capable of identifying infection from 4 to 8 weeks post-exposure. Of the survivors tested, all were negative by PCR and the lethal method, and only one fish was identified as being positive by non-lethal fin histopathology. In another experiment, all three sampling methods were applied to asymptomatic WSIV carriers in a case study conducted at the Kootenai Tribal Sturgeon Conservation Hatchery. Results showed that both lethal and non-lethal fin histopathology were equally effective in detecting infection, but PCR was unable to identify this strain of WSIV. Depending on the virus isolate, these results suggest that non-lethal sampling of fin tissue (histopathology or PCR) is comparable with the lethal sampling method at identifying WSIV infection once infection is established, and under certain circumstances may provide an alternative to lethal sampling.

A new species of nucleo-cytoplasmic large DNA virus (NCLDV) associated with mortalities in Manitoba lake sturgeon Acipenser fulvescens

“…Especially given the limited sensitivity of the test compared to qPCR, absence of verification by a different test method such as cell culture, and the possibility that the virus might persist at extremely low levels as a localized chronic infection in asymptomatic fish. In addition, differences in the ability to detect sturgeon NCLDVs might reflect the choice of tissues sampled or differences in disease susceptibility of the host , Drennan et al 2007, Kurobe et al 2010. The outbreaks at UMAAHF were temporally asynchronous but acute, indicating that a large percentage of the fish were either harboring the virus at the onset of mortality or that the fish were exposed to a high dose of virus on 4 separate occasions.…”

“…WSIV and MRSIV have historically been diagnosed using a combination of histology and electron microscopy. Both viruses localize to the integument of the oropharynx and olfactory organs as well as the fins and in some cases the epithelium of the gills (Hedrick et al 1990, Watson et al 1998b, Drennan et al 2007, Kurobe et al 2011. Microscopic signs of infection include hypertrophied, basophilic or amphophilic-to eosinophilic-staining cells and eccentric nuclei, as well as inclusion bodies containing isometric, doubly encapsidated virus particles displaying a condensed bar-shaped nucleoid (Hedrick et al 1990, 1992, Kurobe et al 2011.…”

Family Iridoviridae: Poor Viral Relations No Longer

“…Preliminary sequence analysis showed little similarity to other known viruses with the exception of partial sequence similarity to the MCP of mimivirus and members of the Iridoviridae and Phycodnaviridae families. A PCR assay has been developed to detect the presence of the WSIV MCP gene (Kwak et al 2006) and has proved effective in the diagnosis of asymptomatically infected individuals (Drennan et al 2007). …”

Characterization of serum and mucosal antibody responses in white sturgeon (Acipenser transmontanus Richardson) following immunization with WSIV and a protein hapten antigen

“…The virus has not been detected in internal organs. In a previous study, our laboratory challenged white sturgeon (mean weight 2.5 g) by intraperitoneal injection or immersion with WSIV [19]. After 126 days at 15 C the injected groups had a cumulative mortality of 58% and the immersion groups 88%.…”

“…White sturgeon iridovirus (Abernathy isolate) was originally isolated from a diseased juvenile white sturgeon from the Abernathy Fish Technology Center (Longview, WA, USA) and repeatedly passed by previously described methods [19]. Viral antigen was obtained by inoculating two 150-cm 2 flasks (Falcon, BD Biosciences, Bedford, MA, USA) containing WSGO tissue culture cell monolayers with pass 3 of WSIV.…”