Showing papers by "Donald V. Lightner published in 1998"

Experimental Infection of Western Hemisphere Penaeid Shrimp with Asian White Spot Syndrome Virus and Asian Yellow Head Virus

Abstract: Postlarval and juvenile stages of four species of western hemisphere penaeid shrimp (Penaeus aztecus, P. duorarum, P. setiferus, and P. vannamei) were experimentally challenged with white spot syndrome virus (WSSV) and yellow head virus (YHV) isolates originating from Asia. Challenge exposures were accomplished by feeding minced tissue from WSSV- or YHV-infected shrimp tissues. The WSSV challenge of postlarval shrimp resulted in severe infections in P. setiferus and P. vannamei and less severe infections in P. aztecus and P. duorarum. The WSSV challenge of juvenile shrimp (∼1 g) resulted in severe infections and 100% cumulative mortality in P. setiferus and P. vannamei, moderate infections and 27% cumulative mortality in P. aztecus, and no signs of infection and 0% cumulative mortality in P. duorarum. The YHV challenge caused serious disease and mortality in juveniles of all four species, but postlarval shrimp appeared resistant to YHV because no virus-related signs of infection, mortality, or di...

Strategies for the control of viral diseases of shrimp in the Americas

Abstract: Viral diseases have severely impacted many of the penaeid shrimp farming industries of the world causing significant production and economic losses. Nearly 20 distinct viruses, or groups of viruses, are known to infect penaeid shrimp. Viruses belonging to the WSSV, MBV, BMN, HPV, IHHNV, and YHV groups have been important pathogens of cultured shrimp in Asia and the Indo-Pacific regions, while TSV, IHHNV, and BP have been the principal viruses of concern in the Americas. Numerous strategies have been attempted for the control of viral diseases in penaeid shrimp aquaculture. These strategies range from the use of improved culture practices (i.e. where sources of virus contamination are reduced or eliminated, sanitation practices are improved, stocking densities are reduced, etc.) to stocking “specific pathogen-free” (SPF) or “specific pathogen resistant” (SPR) species or stocks. In the Americas many strategies have been employed in efforts to reduce production losses due to the enzootic viruses IHHNV, BP, and TSV. Improved husbandry practices have been successfully employed for the control of BP, and for nearly a decade, this virus has seldomly been reported as an economic constraint to successful shrimp culture.Until recently, the popularity and use of the relatively IHHNV resistant species Penaeus vannamei, in preference to the culture of the more IHHNV susceptible P. stylirostris, was characteristic of the shrimp farming industries of the Americas. The popularity of P. vannamei began to decline when TSV emerged as a very serious pathogen of this species in 1992 and then spread to virtually all of the shrimp growing regions of the Americas during the ensuing four years. Because P. stylirostris was found to be innately TSV resistant, two domesticated, genetically selected SPR strains of this species, which are resistant to IHHN disease, are currently being developed and marketed in the Americas. In some regions, these SPR stocks of TSV and IHHNV resistant P. stylirostris are replacing P. vannamei stocks in culture. Other shrimp farming interests are using wild or domesticated stocks of P. vannamei that show improved resistance to TSV. While resistance to TSV was used as a selection criteria for the domesticated stocks of P. vannamei, natural selection for TSV resistance appears to be occurring in wild stocks where TSV has been enzootic for several years. The same selective process for IHHNV resistance seems to be occurring in some wild stocks of P. stylirostris.

Reverse transcription polymerase chain reaction (RT-PCR) used for the detection of Taura syndrome virus (TSV) in experimentally infected shrimp.

Abstract: Taura Syndrome Virus (TSV) has adversely affected the shrimp culture industries of the Americas. First recognized in 1992, this viral agent has spread throughout the shrimp growing regions of South and Central America to become established in North America in the short span of 5 yr. Diagnostic methods for TSV include histopathology, bioassay using susceptible Penaeus vannamei as the indicator species and in situ hybridization with TSV specific complimentary DNA (cDNA) gene probes. An additional method for detecting TSV is through the use of reverse transcription polymerase chain reaction (RT-PCR). Two oligonucleotide primers were selected using the sequence information from a cloned cDNA segment of the TSV genome. The primers, designated 9195 and 9992, used in the RT-PCR procedure amplify a 231 base pair (bp) fragment of the cDNA. Using the RT-PCR technique, TSV has been detected in the hemolymph of P. stylirostris and P. vannamei with experimentally induced TSV infections.

Taura syndrome of penaeid shrimp: cloning of viral genome fragments and development of specific gene probes.

Abstract: The ssRNA genome extracted from purified Taura Syndrome Virus (TSV) was transcribed into double-stranded, blunt-ended cDNA and was used to construct cDNA libraries either in pUC 18 or in pBluescript II KS-vectors. Twelve recombinant plasmids chosen after screening of the libraries were subjected to restriction enzyme digestions for determination of size inserts and restriction maps. Two of them, pP15 and pQ1, were selected for probe construction. The inserts, 1500 and 1300 base pairs (bp) respectively, were DIG-11dUTP-labelled and the corresponding probes were named P15 and Q1. On northern blots and dot blots, using different denaturation methods, the 2 probes hybridized specifically with extracted RNA-TSV genome, TSV and infected TS shrimp homogenates. No positive hybridization was obtained with other shrimp viruses tested [Infectious Hypodermal and Hematopoietic Necrosis Virus (IHHNV) and Hepatopancreatic Parvovirus (HPV)]. The specificity of the 2 probes was confirmed by in situ hybridization on histological sections of TS diseased shrimps.

Isolation and Identification of Mycobacterium peregrinum from the Pacific White Shrimp Penaeus vannamei

Abstract: Mycobacterium peregrinum was isolated from multifocal, melanized nodular lesions in the carapace of the cultured marine shrimp Penaeus vannamei. This is the first identification of this species of Mycobacterium in shrimp. The lesions appeared to be the result of opportunistic infections in otherwise healthy animals. The presence of M. peregrinum in cultured shrimp has a direct negative impact on the marketability of shrimp because it causes obvious black lesions. The potential for accidental infections of shrimp farm or packing plant workers from handling infected shrimp is of concern since nodular skin lesions induced by the bacterium are difficult to treat.

Differentiation of BP-type baculovirus strains using in situ hybridization

Abstract: BP-type viruses infect wild and farmed shrimp species in the Americas and can cause high mortality in larval stages. Histologically, BP disease is characterized by the presence of occlusion bodies (OBs) in the nucleus of hepatopancreatic epithelial cells. By in situ hybridization using different molecular probes, we tested shrimp infected with BP-type viruses collected from several geographical areas. In one shrimp, a case of double infection by 2 different BP-type viruses was noted. This has not been previously reported. The molecular probes recognized only the Pacific strain of BP. This specificity of the probe was confirmed by in situ hybridization tests with some infected shrimp collected from the Atlantic and Pacific coasts. The probes reacted only with infected shrimp obtained from the Pacific coast. These results suggest the existence of at least 2 different BP-type viruses and show that specific probes can be used to differentiate between them.