Detection and distribution of ostreid herpesvirus 1 in experimentally infected Pacific oyster spat

• Viral DNA/RNA localization were studied in oysters by ISH using two virus doses.
• Viral replication was not detected in oysters receiving the lowest virus dose.
• Virus was mainly observed in mantle, gills and heart by ISH using the highest dose.
• Viral detection was significantly different in function of tissues and time.

High mortality rates are reported in spat and larvae of Pacific oyster Crassostrea gigas and associated with ostreid herpesvirus 1 (OsHV-1) detection in France. Although the viral infection has been experimentally reproduced in oyster larvae and spat, little knowledge is currently available concerning the viral entry and its distribution in organs and tissues. This study compares OsHV-1 DNA and RNA detection and localization in experimentally infected oysters using two virus doses: a low dose that did not induce any mortality and a high dose inducing high mortality. Real time PCR demonstrated significant differences in terms of viral DNA amounts between the two virus doses. RNA transcripts were detected in oysters receiving the highest dose of viral suspension whereas no transcript was observed in oysters injected with the low dose. This study also allowed observing kinetics of viral DNA and RNA detection in different tissues of oyster spat. Finally, viral detection was significantly different in function of tissues (p < 0.005), time (p < 0.005) with an interaction between tissues and time (p < 0.005) for each probe.

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