Microscopic and Ultrastructural Studies of Necrotizing Hepatopancreatitis in Pacific White Shrimp (Penaeus vannamei) Cultured in Texas

Abstract

Abstract. Granulomatous hepatopancreatitis of unknown etiology has been considered an important disease of Texas shrimp mariculture since 1985. Samples of Pacific white shrimp (Penaeus vannamei) were collected during 1986, 1987, and 1990 from three farms and an experimental mariculture facility with histories of production loss and increased mortality rates. Histologic and ultrastructural examination of shrimp from the four sites demonstrated two morphologically distinct, Gram-negative, double-enveloped, intracytoplasmic bacteria in necrotic hepatopancreatic epithelium. The more numerous small, pleomorphic rod as well as the helical organism are both taxonomically unclassifiable. The helical organism lacked ultrastructural characteristics of previously described helical or spiral bacteria. The relationship between the two organisms is unknown, but the pleomorphic rod is thought to play a major role in the disease. The role of a bacterial agent(s) in subsequent disease episodes is suggested by the observation that the use of oxytetracycline-medicated feed resulted in increased production and survival. Hepatopancreatic tubular epithelial necrosis and shrimp mortality correlated directly with the extent of infection by the small pleomorphic rod. Individual discrete bacteria were identified microscopically by Steiner and Steiner's method. Three major developmental stages of the disease were characterized based on the extent and number of hepatopancreatic tubular epithelial cells containing bacteria, the degree of tubular interstitial inflammation, and the extent and chronicity of tubular necrosis. Additional studies are needed to clarify the roles of the different bacteria identified and the potential role of environmental factors on the disease process.

Molecular detection methods developed for a systemic rickettsia-like bacterium (RLB) in Penaeus monodon (Decapoda: Crustacea)

“…In situ hybridization assays were used to detect the RLB in Penaeus monodon from the Madagascar epizootic and in experimentally induced laboratory infections of P. vannamei. In addition, other shrimp tissues infected with the NHP agent (Frelier et al 1992), an unidentified shrimp micrococcus (UAZ: origin Madagascar), vibrio (UAZ: origin Mexico) and rickettsial organisms from P. monodon cultured in Malaysia (Anderson et al 1987) and Australia (UAZ: origin Australia) were tested to validate the specificity of the probe. An SPF sample was included in each in situ assay as the negative control.…”

“…To survive and reproduce, the rickettsia organism must enter the eucaryotic host cell, multiply within the cell, exit and reestablish this cycle in another cell (Winkler 1990). Rickettsia-like microorganisms infect a wide range of aquatic crustaceans including amphipods, crabs, freshwater crayfish and prawns (Federici et al 1974, Harshbarger et al 1977, Bonami & Pappalardo 1980, Larrson 1982, Johnson 1984, Brock et al 1986, Anderson et al 1987, Krol et al 1991, Frelier et al 1992, Fryer & Lan-nan 1994, Bower et al 1996, Jimenez & Romero 1997, Edgerton & Prior 1999, Wang & Gu 2002.…”

Bioinformatic analysis of the flagellar system of the rickettsia-like alphaproteobacteria Candidatus Hepatobacter penaei

“…Esta se ha identificado en el orden de las rickettsiales debido a que presenta características endosimbióticas al desarrollarse y multiplicarse dentro de las células epiteliales del hepatopáncreas en varias especies de camarones peneidos: Farfantepenaeus aztecus, F. californiensis, Litopenaeus vannamei, L. setiferus y L. stylirostris (Krol et al 1991, Frelier et al 1992, Lightner et al 1992, Lightner 1996. Es así, que estudios morfológicos han revelado su presencia en el citoplasma y en el epitelio tubular del hepatopáncreas de camarones peneidos (Frelier et al 1992, Lightner et al 1992.…”

“…La bacteria Candidatus Hepatobacter penaei presenta forma de cocobacilo, su tamaño oscila alrededor de 0,32 µm de diámetro mostrando una membrana trilaminar, sin flagelos; tiene una sección transversal constricta en la parte central, indicando replicación por fisión binaria (Krol et al 1991, Frelier et al 1992. Sin embargo, estudios posteriores a estos describen una bacteria helicoidal con dimensiones de 0,59 -1,18 µm de longitud y 0,36 µm de ancho (Loy et al 1996), posee una membrana trilaminar con 8 flagelos en el ápice basal 1 o 2 en la cresta de la hélice (Lightner et al 1992), considerándose dos diferentes etapas de vida.…”

Experimental infection of Penaeus vannamei by a rickettsia-like bacterium (RLB) originating from P. monodon

“…Amphipods, crabs, freshwater crayfish and prawns have been documented to be infected with RLB (Federici et al 1974, Harshbarger et al 1977, Bonami & Pappalardo 1980, Larrson 1982, Johnson 1984, Brock et al 1986, Anderson et al 1987, Krol et al 1991, Frelier et al 1992, Fryer & Lannan 1994, Bower et al 1996, Jimenez et al 1997, Edgerton & Prior 1999, Wang & Gu 2002, Nunan et al 2003. The purpose of this study was to determine whether the RLB that caused severe mortalities in Penaeus monodon could infect and cause mortalities in specific pathogen free (SPF) P. vannamei.…”