Necrotizing hepatopancreatitis in Penaeus vannamei : molecular phylogeny and detection of the etiologic agent and pathogenesis in an experimental model of the disease /
Necrotizing hepatopancreatitis (NHP) is a severe disease of
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1994.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=743238911&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | Necrotizing hepatopancreatitis (NHP) is a severe disease of farm-raised Pacific white shrimp (Penaeus vannamei) that has been associated with mortalaties approaching 95%. The etiology of NHP is a pleomorphic, Gram-negative bacterium. The NHP bacterium has not been cultivated in vitro and little is known about the life cycle of the NHP bacterium outside the shrimp host epithelial cell. In this study, we used the polymerase chain reaction (PCR) to amplify the gene that encodes the 16S ribosomal RNA (16S RDNA) of the NHP bacterium. The amplified 16S RDNA was then cloned and sequenced. Phylogenetic analysis of the sequenced 16S RDNA enabled placement of NHP bacterium in the (X-Proteobacteria. As phylogenetic categories are predictive, the information that is known about one organism can generally be applied to its relatives. Using information derived from the phylogenetic classification.of the NHP bacterium, potential reservoir hosts and environmental sources of the organism are currently being investigated. In addition, the 16S RDNA sequence was used to develop a sensitive and specific PCR detection assay and a NHP bacterium-specific 16S RDNA probe. In this study, the PCR assay was used to confirm NHP in shrimp cultured in Texas and Peru. The DNA probe was tested in an in situ hybridization assay and was shown to be efficacious for early detection of the NHP bacterium in infected shrimp. Using electron microscopy and in situ hybridization, the temporal pathogenesis of NUP was investigated. In this study, we demonstrated that the initial infection most likely occurs through endocytosis of the NHP bacterium by the epithelial cell and the NHP bacterium is spread to adjacent hepatopancreatic epithelial cells through lateral transmission. In this study, we demonstrated that the NHP bacterium can be degraded by the shrimp epithelial cell, provided that the organism is confined to the phagosome. If, however, the NHP bacterium escapes from the phagosome it can replicate within the cytoplasm to reach the massive numbers seen in the natural infections. These findings have important implicafions in the efficacious treatment of NHP. |
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| Item Description: | Vita. "Major Subject: Veterinary Pathology". |
| Physical Description: | xiii, 130 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references. |