A parvo-like virus in cultured redclaw crayfish Cherax quadricarinatus from Queensland, Australia

Abstract

In the summer of 1999/2000, an epizootic occurred in cultured juvenile redclaw crayfish Cherax quadricarinatus on one commercial crayfish farm in northern Queensland, Australia. Mortalities occurred over 4 wk, with up to 96% cumulative mortalities in 2 earthen ponds stocked with juveniles. The crayfish were weak, anorexic and lethargic. A transmission trial was conducted, using filtered, cell-free extract prepared from infected crayfish as inoculum. The disease was reproduced, with on-going mortalities occurring in inoculated crayfish over 55 d. Experimentally inoculated crayfish showed gross signs of malaise, anorexia and disorientation before dying. Two types of intranuclear inclusion bodies (INIBs) were seen in tissues of endodermal, ectodermal and mesodermal origin by light microscopy with haematoxylin and eosin (H&E) stained sections. 'Early'-stage INIBs were eosinophilic, rounded and located centrally within slightly enlarged nuclei while 'late'-stage INIBs were well-rounded and deeply basophilic. The gills, cuticular epithelium and epithelial cells of the foregut, midgut and hindgut were the most heavily infected tissues. By transmission electron microscopy, virions with an average diameter of 19.5 nm were seen within electron-dense granular inclusion bodies within enlarged nuclei of both naturally and experimentally infected crayfish. The size of the virions and cytopathology are consistent with characteristics of viruses in the Family Parvoviridae. This is the first reported case of mass mortality caused by a parvo-like virus infection in C. quadricarinatus. KEY WORDS:Cherax quadricarinatus · Virus · Parvo-like virus · Disease · Aquaculture · Crayfish · Pathology Resale or republication not permitted without written consent of the publisherDis Aquat Org 50: [79][80][81][82][83][84][85][86] 2002 clinical viral infections have been reported (Edgerton et al. 1994, Edgerton & Owens 1999, but crayfish with these infections have usually been coinfected with bacterial and/or other pathogens. Mass mortalities in pond-reared redclaw have so far been caused by bacterial diseases including vibriosis (Eaves & Ketterer 1994) and those due to infections with rickettsiales-like organisms (Ketterer et al. 1992).In December 1999 and January 2000, 1 redclaw crayfish farm in Queensland, Australia, reported higher than average mortalities in 2 earthen ponds stocked with juvenile crayfish Cherax quadricarinatus. Cumulative mortalities of up to 96% occurred over 2 mo. Histopathological examination of diseased crayfish revealed intra-nuclear inclusion bodies that resembled those associated with parvo-like viral infections. In February 2000, on-going mortalities occurred in other ponds on this farm stocked with adult crayfish. There was an estimated 50% loss in total farm production, due to losses of juvenile and adult crayfish and the farm subsequently closed down for a total destocking and pond disinfection. A detailed disease investigation was carried out to determine the cause of the mortalities.The results an...

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