Ultrastructure and pathogenesis of Monodon ž / baculoÕirus Pm SNPV in cultured larvae and natural brooders of Peneaus monodon

Ž . Monodon baculoÕirus 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 reduced feeding and preening activities while infected juveniles, sub-adults and brooders exhibited normal behaviour. MBV-infected hepatopancreatic cells exhibited a 300% volume increase in the hypertrophied nuclei, which contained eosinophilic, spherical, intranuclear occlusion bodies. At the apical cell surface, the number of microvilli were greatly reduced by cytolysis. The 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 occluded 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 occlusion bodies consisted of non-crystalline, granulin-like sub-units each measuring 12 nm in diameter and contained mostly non-occluded virions measuring 326"4 nm long and 73"1 nm wide. In the zoea, mysis and post-larvae, the average infection rates for ) Corresponding author. Tel.: q44-1232-272083; fax: q44-12342-236505; e-mail: [email protected] 0044-8486r00r$ see front matter q 2000 Elsevier Science B.V. All rights reserved. Ž . PII: S0044-8486 99 00317-8 ( ) P. Ramasamy et al.rAquaculture 184 2000 45–66 46 MBV were 28%"2%, 57%"3% and 91%"1%, respectively. Mortality rates were greater in the infected than in the uninfected post-larvae, at 81%"0% and 11%"0%, respectively. The mortality rate in MBV infected zoea and mysis was 23%"3% and 49%"2%, respectively, 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 uninfected larvae. q 2000 Elsevier Science B.V. All rights reserved.