Reo-like virus in white shrimp Penaeus van-namei (Crustacea: Decapoda): co-occurrence with Baculovirus penaei in experimental infections

Abstract

A virus, tentatively identified as reo-like, occurred concurrently with experimentallyinduced Baculovirus penaei (BP) infection in cultured white shrimp larvae Penaeus vannamei. Each shrimp with a reo-like viral infection also had a BP infection, but not all BP-infected shrimp had a reolike infection. Both viruses occurred in the same tissues and occasionally withln the same cell. The reolike virus developed in epithelia1 cells of the anterior midgut and in reserveand fibrillar-cells of the hepatopancreas. The paraspherical and non-enveloped reo-like virions (ca 50 nm diam.) occurred as unordered aggregates in the cell cytoplasm. Their etiology has not been determined. Reo-like vinons may have been ~ntroduced along with the BP virus, or, were latent and only manifested due to stress induced by the more pathogenic BP virus. INTRODUCTION epithelium. This reo-like virus occurred only in specimens infected with BP. Here, we report on the ultraRed-like viruses have been reported in several structure and cytopathology of this virus and its relaspecies of crabs and shrimp. The paralysis virus of the tionship to BP. portunid crab Macropipus depurator (Vago 1966, Bonami 1973, Bonami et al. 1976, Bergoin et al. 1982) and the reo-like virus of the blue crab Callinectes MATERIAL AND METHODS sapidus (Johnson & Bodammer 1975, Johnson 1977, 1984), are associated with fatal paralysis of their hosts. Naupli stage Penaeus vannamei were purchased In the Mediterranean shore crab Carcinus mediterfrom a commercial hatchery. Approximately 150 larvae raneus, a highly pathogenic, sometimes fatal, reo-like were placed in each of ten 1 1 Imhoff setthng cones. virus infecting the gill epithelium (Bonami 1977, BerWhen larval shrimp developed to the Protozoeal I11 goin et al. 1982), and a reo-like virus, of undetermined stage, larvae in 5 of the cones were ~nfected with BP pathogenicity, infecting the hepatopancreatic epithevirus. Larvae in the other 5 cones served as controls; lium (Man & Bonami 1987) have been reported. With they were not exposed to viral material and were mainregard to shrimp, reo-like virus appeared to have tained in a separate, virus-free room. limited pathogenicity in the kuruma shrimp Penaeus Details of experimental infection protocols have been japonicus (Tsing & Bonami 1987). Nash et al. (1988) reported elsewhere (Overstreet et al. 1988). Briefly, recently reported a reo-like virus in dying giant tiger rotifers Branchionus plicatilis were fed minced larval shrimp P. monodon, but could not determine whether shrimp tissues with microscopically confirmed BP the virus was the cause of death. Most of these reo-like infections. The BP-infected tissues had been collected viruses occur along with other viral infections, or are from previous bioassays and stored at -70°C. Tissues associated with other diseases in the same host. were thawed and pulverized into a paste. Rotifers were During studies on the effects of Baculovirus penaei exposed to the BP-infected tissues for 2 to 3 h and then (BP) in larval white shrimp Penaeus vannamei, we fed to shrimps. After protozoeal shrimp were exposed observed a second virus tentatively identified a s a reoto rotifers for 26 h, rotifers and uneaten debris were like virus in the midgut and hepatopancreatic removed and the water replaced. Both experimentally O Inter-Research/Printed in F. R. Germany 46 Dis aquat. Org. 8: 45-49, 1990 infected and negative control larvae were maintained in cones and fed a diet of brine shrimp Arteni~a salina. Exposed and control larvae were examined by light and electron microscopy at 96, 117.5 and 142 h post shrimp-exposure. For electron microscopy, shrimp were cut into cephalothorax and tail portions and fixed in 2.0 O/o glutaraldehyde in 0.025 M sodium cacodylate buffered seawater. Specimens were postfixed in 1.0 % osmium tetroxide in 0.1 M sodium cacodylate buffer, dehydrated in a graded series of ethanols, and embedded in Spurr's resin (Spurr 1969). Specimens were oriented in flat molds so that cross-sections of cephalothorax could be examined for systemic viral infection. Ultrathin sections were stained with uranyl acetate and lead citrate (Reynolds 1963) and examined with a JEOL 100 SX electron microscope at 60 KV.