Ultrastructure and pathogenesis of Monodon baculovirus (Pm SNPV) in cultured larvae and natural brooders of Peneaus monodon

Monodon baculovirus (MBV) occurred in the hepatopancreas of cultured larvae , zoea, mysis and post-larvae and in wild caught juveniles, sub-adults and brood stocks of Penaeus monodon. Infected larvae exhibited lethargy and red uced feeding and preening activities while infected juveniles, sub-adults a nd brooders exhibited normal behaviour. MBV-infected hepatopancreatic cells exhibited a 300% volume increase in the hypertrophied nuclei, which contai ned eosinophilic, spherical, intranuclear occlusion bodies. At the apical c ell surface, the number of microvilli were greatly reduced by cytolysis. Th e cytoplasm contained numerous vacuoles and few mitochondria. Two types of occlusion bodies were observed. Type 1 comprised a paracrystalline array of polyhedrin sub-units with a lattice spacing of 5-7 nm, with numerous occlu ded virions and a few non-occluded virions in the periphery within a double envelope measuring 267 +/- 2 nm long and 78 +/- 3 nm wide. Type 2 occlusio n bodies consisted of non-crystalline, granulin-like sub-units each measuri ng 12 nm in diameter and contained mostly non-occluded virions measuring 32 6 +/- 4 nm long and 73 +/- 1 nm wide. In the zoea, mysis and post-larvae, t he average infection rates for MBV were 28% +/- 2%. 57% +/- 3% and 91% +/- 18, respectively. Mortality rates were greater in the infected than in the uninfected post-larvae, at 81% +/- 0% and 11% +/- 0%, respectively. The mor tality rate in MBV infected zoea and mysis was 73% +/- 3% and 49% +/- 2%, r espectively, while in the uninfected larvae. it was 5% +/- 0% and 8% +/- 0% , respectively. The mortality rate for the infected and uninfected nauplii was similar at 3% +/- 0%. In the brood stocks, the infection rate was 21% /- 1% while in the juveniles and sub-adults. it was lower at 4% +/- 0% and 5% +/- 1%. MBV infected larvae harboured 10 times more bacteria than uninfe cted larvae. (C) 2000 Elsevier Science B.V. All rights reserved.