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Diseases of Aquatic Organisms

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DAO 50:79-86 (2002)  -  doi:10.3354/dao050079

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

Rachel O. Bowater1,*, Max Wingfield2, Andrew Fisk1, Kelly M. L. Condon1, Angela Reid1, Howard Prior3, Elizabeth C. Kulpa1

1Queensland Department of Primary Industries, Animal and Plant Health Service, Oonoonba Veterinary Laboratory, PO Box 1085 Townsville, Queensland 4810, Australia
2Queensland Department of Primary Industries, Bribie Island Aquaculture Research Centre, PO Box 2066, Bribie Island, Queensland 4507, Australia
3Queensland Department of Primary Industries, Animal Research Institute, 665 Fairfield Road, Yeerongpilly, Queensland 4105, 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 intra-nuclear inclusion bodies (INIBs) were seen in tissues of endodermal, ectodermal and mesodermal origin by light microscopy with haematoxylin and eosin (H&E) stained sections. ŒEarly¹-stage INIBs were eosinophilic, rounded and located centrally within slightly enlarged nuclei while Œlate¹-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

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