Abstract

Microscopical findings from moribund Kuruma shrimp larvae, P. japonicus showed no evidence of any polyhedral inclusion bodies in either squash preparations of the affected mid-gut gland or in preparations stained by Vago-Amargier's method. Pathological changes were remarkable cellular necrosis and collapse of mid-gut gland. It was noted that nuclear hypertrophy and collapse always followed these cellular changes. Electron microscopical findings showed cytoplasmic collapse of mid-gut gland cells and the nuclear hypertrophy resulting in karyorrhexis, as well as virions and incomplete viral particles representing virogenic stages in the affected nuclei. The average length and diameter of virions was 310 nm and 72 nm respectively, and length of the nucleocapsids was 250 nm. Infectivity trials carried out employing oral and water borne inoculations revealed high cumulative mortality to healthy shrimp larvae.