Description of a small dsRNA virus from freshwater crayfish Cherax quadricarinatus

Abstract

A unique hepatopancreocyte nuclear pathology was seen during a histological survey of farmed crayfish Cherax quadncannatus Later, the pathology was associated with mortalities in laboratory-held juvenlle populations Affected nuclel were vanably hypertrophic, had marginated and clumped chromatin and were almost fully occupied by numerous amorphous inclusions in late infections Well-developed inclusions were intensely purple-red whllst less-developed inclusions were eosinophilic with H&E The nucleolus remained identifiable and centrally located Embryonic (E) cells were the only hepatopancreocyte type that did not display the changes Crayfish from all 7 farms surveyed were infected, wlth a maximum prevalence of 52 3 % The intensity was extremely low in adult crayfish The inclusions were present in 10 of 14 crayfish families used in a hentability study Mortalities vaned greatly with the highest mortality being 85 % by Week 8 Monbund crayfish consistently displayed a hlgh intensity of affected nuclei Affected nuclei were Feulgen and methyl-green negatlve pyronin positive and fluoresced yellow-green with acndine orange, suggesting the pathology was associated with a double-stranded RNA virus Nuclease digestion of the histological matenal confirmed the predominance of dsRNA in the inclusions Transmission electron microscopy revealed 25 nm vinons in highly ordered intranuclear paracrystalline arrays, a feature apparently unique amongst the RNA viruses The virus is morphologically and morphogenically simllar to Glardia lambha virus and is therefore named Cherax G~ardlavlrus-like virus