To date, the infectivity of OsHV-1 was univocally demonstrated towards early stages of C. Results of diagnostic tests indicated that OsHV-1 was detected in most of samples collected during mortality outbreaks and especially in moribund oysters (Garcia et al., unpublished data). Data available in literature and those collected during an epidemiological survey conducted by the French National Network for Surveillance and Monitoring of Mollusc Health (Repamo) between 19 suggested a causal link between spat mortality and OsHV-1 detection in France (Garcia et al., unpublished data). Herpes-like virus infections have then been noticed worldwide in several other mollusc species in association with massive mortality episodes, such as in oysters, in clams, in scallops and in abalone. in the eastern oyster Crassostrea virginica. The first description of a virus morphologically similar to herpes viruses was reported by Farley et al. These recurrent mortality events have been mainly associated to the detection of the ostreid herpesvirus 1 (OsHV-1), the sole member of the Malacoherpesviridae family. Mortality outbreaks took place currently during the summer period from mid May to July concomitantly with a rapid increase of seawater temperature (Garcia et al., unpublished data). These mortalities were usually sudden and severe (up to 100%), and affected essentially spat (oysters less than one year old) and juveniles (12 to 18 month old oysters). gigas oysters in the field and in hatcheries/nurseries. However, since the late 80's abnormal mortality events have been reported in France among C. angulata related to irido-like virus infections. This species has been introduced in France from Canada and Japan in the early 70's after the extinction of the Portuguese oyster C. The French oyster production is essentially based on the rearing of the Pacific cupped oyster, Crassostrea gigas. The yearly European oyster production is the 126 000 tonnes, France being the leading Member State (115 000 tonnes/year). The oyster industry has grown to be very important for many regions of the world contributing substantially to social and economic activity in the coastal zones. World mollusc aquaculture is characterised by a focus on a limited number of species including oysters being raised at an industrial level. The developed protocol allowed to maintain sources of infective virus which can be useful for the development of further studies concerning the transmission and the development of OsHV-1 infection. Finally, TEM analysis demonstrated the presence of herpes virus particles. Furthermore, analysis of injected oyster spat revealed the detection of high amounts of OsHV-1 DNA by real-time quantitative PCR. Moreover, filtered tissue homogenates induced mortalities whereas the same tissue homogenates exposed to an ultraviolet (UV) treatment did not induce any mortality suggesting that oyster spat mortalities require the presence of a UV sensitive agent. Results of the experimental trials showed that mortalities were induced after injection. This protocol was based on the intramuscular injection of filtered (0.22 μm) tissue homogenates prepared from naturally OsHV-1 infected spat collected on French coasts during mortality outbreaks in 2008. In this study, an experimental protocol to reproduce OsHV-1 infection in laboratory conditions was developed. Diagnostic tests indicated that OsHV-1 including a particular genotype, termed OsHV-1 μVar, was detected in most of samples and especially in moribund oysters with the highlighting of virus particles looking like herpes viruses by TEM examination. Different hypothesis including the implication of environmental factors, toxic algae and/or pathogens have been explored. In 20, acute mortalities occurred in France among Pacific cupped oyster, Crassostrea gigas, spat.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |