DESCRIPTION OF A SMALL DSRNA VIRUS FROM FRESH-WATER CRAYFISH CHERAX-QUADRICARINATUS

A unique hepatopancreocyte nuclear pathology was seen during a histolo gical survey of farmed crayfish Cherax quadricarinatus. Later, the pat hology was associated with mortalities in laboratory-held juvenile pop ulations. Affected nuclei were variably hypertrophic, had marginated a nd clumped chromatin and were almost fully occupied by numerous amorph ous inclusions in late infections. Well-developed inclusions were inte nsely purple-red whilst less-developed inclusions were eosinophilic wi th H&E. The nucleolus remained identifiable and centrally located. Emb ryonic (E) cells were the only hepatopancreocyte type that did not dis play the changes. Crayfish from all 7 farms surveyed were infected, wi th a maximum prevalence of 52.3 %. The intensity was extremely low in adult crayfish. The inclusions were present in 10 of 14 crayfish famil ies used in a heritability study. Mortalities varied greatly, with the highest mortality being 85 % by Week 8. Moribund crayfish consistentl y displayed a high intensity of affected nuclei. Affected nuclei were Feulgen and methyl-green negative, pyronin positive and fluoresced yel low-green with acridine orange, suggesting the pathology was associate d with a double-stranded RNA virus. Nuclease digestion of the histolog ical material confirmed the predominance of dsRNA in the inclusions. T ransmission electron microscopy revealed 25 run virions in highly orde red intranuclear paracrystalline arrays, a feature apparently unique a mongst the RNA viruses. The virus is morphologically and morphogenical ly similar to Giardia lamblia virus and is therefore named Cherax Giar diavirus-like virus.