Picorna-like virus associated with mortality and a spongious encephalopathy in grouper Epinephelus malabaricus

A picorna-like virus was detected from diseased fry and fingerling grouper Epinephelus malabaricus cultured in southern Thailand. Affected grouper exhibited dark coloration of the head and tail, loss of equilibrium and corkscrew-like swimming. Pathological changes of affected fish showed vacuolating encephalopathy and retinopathy. Intracytoplasmic inclusions were observed in the nerve cells. From electron microscopic studies, virus particles could be detected in the brain and eyeball of affected fishes. They were round to icosahedral, without an envelope, 20 to 25 nm in diameter and had an electron dense core of 16 nm. Filtrates (0.45 mu m) of affected brain and eyeball tissues can produce the same clinical signs in healthy grouper after injection, and the identical virus particles could be observed in the brain and retina of experimentally infected fish.