DAO 122:43-55 (2016)  -  DOI: https://doi.org/10.3354/dao03062

In situ hybridization and histopathological observations during ostreid herpesvirus-1-associated mortalities in Pacific oysters Crassostrea gigas

Rudolfo Bueno1,*, Matthew Perrott2, Magda Dunowska2, Cara Brosnahan1, Colin Johnston1,3

1Animal Health Laboratory, Investigation, Diagnostic Centres and Response—Wallaceville, Ministry for Primary Industries, 66 Ward St, PO Box 40742, Upper Hutt 5018, New Zealand
2Institute of Veterinary, Animal & Biomedical Sciences, Massey University Manawatu (Turitea) Tennent Drive, Palmerston North 4474, New Zealand
3Present address: Aquaculture New Zealand, Level 1 Wakatu House, Montgomery Square, Nelson 7010, New Zealand
*Corresponding author:

ABSTRACT: In a previous longitudinal study conducted during a mortality investigation associated with ostreid herpesvirus-1 (OsHV-1) microvariant in New Zealand Pacific oysters in 2010-2011, temporality of OsHV-1 nucleic acid detection by real-time PCR assay and onset of Pacific oyster mortality was observed. The present study further elucidated the role of OsHV-1 using an in situ hybridization (ISH) assay on sections of Pacific oysters collected from the same longitudinal study. Hybridization of the labelled probe with the target region of the OsHV-1 genome in infected cells was detected colorimetrically using nitro blue tetrazolium (NBT). OsHV-1 presence and distribution in spat indicated by the ISH signal was then compared with the existence of pathological changes in oyster tissues. Dark blue to purplish black NBT cell labelling was seen predominantly in the stroma of the mantle and gills at Day 5 post introduction to the farm. The distribution and location of ISH signals indicated the extent of OsHV-1-infected cells in multiple tissues. Histopathological abnormalities were mostly non-specific; however, a progressive pattern of increasingly widespread haemocytosis coincided with the appearance of OsHV-1-infected cells in spat collected at different time-points. The visualisation of an increasing number of OsHV-1-positive cells in spat prior to a marked increase in mortality indicated the strong likelihood of an on-going and active viral infection in some oysters. Further studies are recommended to elucidate OsHV-1 pathogenesis in Pacific oysters in association with other potentially causal variables, such as elevated temperature and interaction with Vibrio spp. bacteria.


KEY WORDS: Ostreid herpesvirus-1 · Microvariant · μVar · Pacific oysters · Crassostrea gigas · In situ hybridization


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Cite this article as: Bueno R, Perrott M, Dunowska M, Brosnahan C, Johnston C (2016) In situ hybridization and histopathological observations during ostreid herpesvirus-1-associated mortalities in Pacific oysters Crassostrea gigas. Dis Aquat Org 122:43-55. https://doi.org/10.3354/dao03062

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