Study on pathogens from outbreaks of Pacific white shrimp Litopenaeus vannamei red-body disease in main cultured area of Zhejiang Province
Pacific white shrimp (Litopenaeus vannamei) is one of the most important commercially cultured aquaculture species around the world. Zhejiang Province represents as one of the main cultured areas in China. In recent years, concurrent with the rapid expanding and intensifying of aquaculture, infectio...
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| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Zhejiang University Press
2014-11-01
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| Series: | 浙江大学学报. 农业与生命科学版 |
| Subjects: | |
| Online Access: | https://www.academax.com/doi/10.3785/j.issn.1008-9209.2014.01.211 |
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| Summary: | Pacific white shrimp (Litopenaeus vannamei) is one of the most important commercially cultured aquaculture species around the world. Zhejiang Province represents as one of the main cultured areas in China. In recent years, concurrent with the rapid expanding and intensifying of aquaculture, infectious diseases in Pacific white shrimp L. vannamei have been steadily increasing. Red-body disease is one of the most common and severe diseases of Pacific white shrimp. From 2011 to 2013, recurrent outbreaks of Pacific white shrimp red-body disease occurred in large-scale breeding farms within the main cultured area of Zhejiang Province, which caused severe economic losses to the shrimp culture industry. Affected shrimps showed typical signs of red bodies, irregular black spots, listless swimming on water surface and reduced feed activities, accompanying with mass mortalities.This study was conducted to investigate the bacterial and viral pathogens from 2012—2013 outbreaks and to illuminate their molecular characteristics and antimicrobial sensitivities, which were compared with those from 2011 outbreak. Using Vitek biochemical test, 16S rRNA sequence analysis and virus specific polymerase chain reaction, Vibrio parahaemolyticus and infectious hypodermal and haematopoietic necrosis virus (IHHNV) were simultaneously identified from the diseased Pacific white shrimps of 2012—2013 outbreaks, but except V. parahaemolyticus, IHHNV was not detected from the diseased ones of 2011 outbreak; meanwhile, Taura syndrome virus (TSV) and white spot syndrome virus (WSSV) were not detected from the diseased Pacific white shrimps of 2011—2013 outbreaks. Although V. parahaemolyticus was positive from all outbreaks during three years, these isolates exhibited remarkable genetic diversity by multilocus sequence typing (MLST) based on the concatenated genes dnaE-gyrB-recA-dtdS-pntA-pyrC-tnaA. The isolates from the same year belonged to multiple sequence types (STs), originated from distinct clones located on separate sub-branches, and the isolates from 2012—2013 outbreaks underwent high level of molecular variation with distinct allelic profiles and STs as compared with from 2011 outbreak. ST414 and ST114 represented dominant STs from 2011 outbreak and 2012—2013 outbreaks, respectively. Novel STs, ST918 (registration No. id-1353) and ST919 (registration No. id-1354), had been confirmed and deposited in the PubMLST database. All of these isolates from 2011—2013 outbreaks belonged to the pandemic group, which was responsible for the majority of clinical cases since 1996, determined by specific molecular markers, i. e., a unique sequence within the toxRS operon encoding transmembrane proteins involved in the regulation of virulence-associated genes, and VPA1168 within an 16-kb insertion which encoded a hypothetical protein with approximate 80% similarity to the Mn<sup>2+</sup> and Fe<sup>2+</sup> transporter. Also, these isolates displayed the same virulence-associated gene profile, containing thermolabile hemolysin (encoded by tlh) and type Ⅲ secretion systems 1 (T3SS1) but lacking thermostable direct hemolysin (encoded by tdh), TDH-related hemolysin (encoded by trh) and type Ⅲ secretion systems 2 (T3SS2). These results revealed that these isolates were atypical virulent isolates (tdh<sup>+</sup> and/or trh<sup>+</sup>) or atypical pandemic group isolates (mostly tdh<sup>+</sup>trh<sup>-</sup>). Absence of tdh and trh, which had traditionally been thought to be critical for the virulence of Vibrio, did not lead to the reduction of bacterial pathogenicity. Moreover, these isolates also showed elevated level of resistance against antimicrobials, especially aminoglycoside.In conclusion, Pacific white shrimp red-body disease might be caused by multiple infections with bacterial and viral pathogens. It is necessary to develop the surveillance system of pathogens implicated in red-body disease, and to clarify the pathogenic mechanism of polymicrobial infection to establish comprehensive prevention and control schemes. |
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| ISSN: | 1008-9209 2097-5155 |