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Cause Of EMS Shrimp Disease Identified
After months of investigation by a research team led by Donald Lighter at the University of Arizona, the elusive pathogen causing early mortality syndrome (EMS), an emerging shrimp disease in Southeast Asia more technically known as acute hepatopancreatic necrosis syndrome (AHPNS), has been identified.
The researchers found that EMS is caused by a bacterial agent, which is transmitted orally, colonizes the shrimp gastrointestinal tract and produces a toxin that causes tissue destruction and dysfunction of the shrimp digestive organ known as the hepatopancreas. It does not affect humans.
Lightner’s team identified the EMS/AHPNS pathogen as a unique strain of a relatively common bacterium,Vibrio parahaemolyticus, that is infected by a virus known as a phage, which causes it to release a potent toxin. A similar phenomenon occurs in the human disease cholera, where a phage makes the Vibrio cholerae bacterium capable of producing a toxin that causes cholera’s life-threatening diarrhea.
Research continues on the development of diagnostic tests for rapid detection of the EMS/AHPNS pathogen that will enable improved management of hatcheries and ponds, and help lead to a long-term solution for the disease. It will also enable a better evaluation of risks associated with importation of frozen shrimp or other products from countries affected by EMS.
Some countries have implemented policies that restrict the importation of frozen shrimp or other products from EMS-affected countries. Lightner said frozen shrimp likely pose a low risk for contamination of wild shrimp or the environment because EMS-infected shrimp are typically very small and do not enter international commerce. Also, his repeated attempts to transmit the disease using frozen tissue were unsuccessful.
Since EMS was first reported in China in 2009, it has spread to Vietnam, Malaysia and Thailand, and now causes annual losses more than U.S. $1 billion. EMS outbreaks typically occur within the first 30 days after stocking a newly prepared shrimp pond, and mortality can exceed 70%.
In an effort to learn from past epidemics and improve future policy, the World Bank and the Responsible Aquaculture Foundation, a charitable education and training organization founded by the Global Aquaculture Alliance, initiated a case study on EMS in Vietnam in July 2012. Its purpose was to investigate the introduction, transmission and impacts of EMS, and recommend management measures for the public and private sectors.
The study team included Lightner, who with University of Arizona co-workers recently identified the EMS/AHPNS pathogen. At a panel discussion on EMS at the Global Aquaculture Alliance’s GOAL 2012 meeting in October 2012, Lightner and Timothy Flegel speculated that the elusive nature of the disease might be explained by a bacteriophage.
EMS is among the topics that will be addressed at GAA’s GOAL 2013 conference in Paris, France, from Oct. 7 to 10.
GAA：EMS病原已被证实
中国水产频道独家报道，2013年5月1日 -全球水产养殖联盟（GAA）在周三宣布，亚利桑那大学Donald Lighter所领导的研究团队经过数月的调查研究，发现了导致早期死亡综合症（EMS）的病原体。在东南亚，这种新兴的疾病被称为急性肝胰腺坏死综合征（AHPNS）。
研究人员发现，EMS的病原体是一种细菌。该菌通过摄食传播，寄生在虾消化道，并产生毒素。这种毒素能够引起组织的破坏和肝胰腺（虾的消化器官）功能紊乱，但不会影响人类。
Lightner的研究小组证实了EMS/ AHPNS的病原体是一类比较常见菌属的独特菌株——副溶血弧菌，经噬菌体感染后，它会释放出强毒性的毒素。类似的现象发生在人类身上就是霍乱，其原理是噬菌体寄生使得霍乱弧菌能够产生一种毒素，导致感染者产生严重腹泻，从而危及生命。
GAA说研究团队将继续致力于开发快速检测EMS / AHPNS病原体的方法，从而提高孵化场和养殖场的对该病的管理能力，进而找到长期的解决方案。同时，这种快速的检测方法也将有利于受EMS影响国家生产的冷冻虾或其他相关产品更好地通过出口的相关的风险评估。
有些国家已经实施了限制从受EMS影响的国家进口的冷冻虾或其他产品的政策。但研究表明，冷冻虾可能对野生虾或环境的污染影响不大，因为EMS感染的虾通常都非常小，不会进入国际贸易。此外，研究组反复尝试使用含菌冷冻组织感染健康个体的实验也均告失败。
EMS是2009年在中国首次报道，现在已经蔓延到越南，马来西亚和泰国，每年造成的损失超过10亿美元。EMS通常暴发在养殖时间不超过30天的虾塘里，死亡率超过70％。
为吸取过往流行病经验，以改善未来疾病状况，世界银行和Responsible Aquaculture Foundation（负责任的水产养殖慈善基金会，由全球水产养殖联盟成立的教育和培训机构）于2012年7月在越南发起EMS的病例研究。其目的是调查EMS的传染源，传播途径和影响，并为公共与私营单位提供相应管理措施建议。
该研究团队的Lightner与亚利桑那大学的同事最近确定了EMS/ AHPNS病原体。在2012年10月举行的全球水产养殖联盟峰会上，在小组讨论中Lightner和Timothy Flegel曾预测EMS这种令人难以捉摸的疾病可能与噬菌体相关。
定于2013年10月7日到10日在法国巴黎举行的GAA会议上，关于EMS的研究将被继续探讨。
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发表于 2013-5-6 11:30:51
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