Abstract
High levels of ostreid herpesvirus 1 (OsHV-1) were detected in hemocytes of OsHV-1 infected mollusks. Mollusk hemocytes are comprised of different cell types with morphological and functional heterogeneity. Granular cells are considered the main immunocompetent hemocytes. This study aimed to ascertain if OsHV-1 infects specific types of hemocytes in ark clams. Types of hemocytes were first characterized through microexamination and flow cytometry. In addition to a large group of red cells, there were three types of recognizable granular cells in ark clams. Type II granular cells were mostly found with OsHV-1 infection by transmission electron microscope (TEM) examination, and represented the hemocyte type that was susceptible to OsHV-1 infection. The subcellular location of OsHV-1 particles in apoptotic type II granular cells was further analyzed. Some OsHV-1 particles were free inside the apoptotic cells, which may contribute to OsHV-1 transmission among cells in the host, some particles were also found enclosed inside apoptotic bodies. Apoptosis is an important part of the host defense system, but might also be hijacked by OsHV-1 as a strategy to escape host immune attack. Following this investigation, a primary culture of type II granular cells with OsHV-1 infection would facilitate the research on the interaction between OsHV-1 and mollusk hosts.
Highlights
Herpes-type viruses were first reported in the diseased oyster Crassostrea virginica in 1972 [1].After that, summer mass mortalities of molluscs have been detected with the herpesvirus infection.Nearly total mortality of Crassostrea gigas, Ostrea edulis and Ruditapes philippinarum larvae had been reported with herpesvirus infection in French hatcheries since the 1990s [2,3,4]
Compared with the control group, significant increase of ostreid herpesvirus 1 (OsHV-1) loads could be detected in all tested tissues including hemocytes, mantle, gill, hepatopancrease, and adductor muscle and foot
The presence of OsHV-1 particles in the hemocytes, hepatopancrease and mantle of infected ark clams was further examined by transmission electron microscope (TEM)
Summary
Summer mass mortalities of molluscs have been detected with the herpesvirus infection. Total mortality of Crassostrea gigas, Ostrea edulis and Ruditapes philippinarum larvae had been reported with herpesvirus infection in French hatcheries since the 1990s [2,3,4]. The herpesvirus was subsequently isolated from infected C. gigas larvae, was sequenced and classified as a member of the herpesviridae under the name ostreid herpesvirus 1 (OsHV-1) [5]. OsHV-1 infection associated mass mortalities of mollusk constantly arose [6,7,8]. The overall structure of OsHV-1 capsid is similar to those of other previously reported herpesviruses with a highly ordered icosahedral-shape nucleocapsid of about 120 nm in diameter [5]
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