Identification of the pathogen responsible for shrimp early mortality syndrome (EMS) opens the door to better understanding and potentially a return to growth in the industry.
Early mortality syndrome (EMS), which is more correctly known as acute hepatopancreatic necrosis syndrome (AHPNS), is caused by a unique strain of the bacterial agent Vibrio parahaemolyticus. Identified by researchers at the University of Arizona, the bacterium when infected by a phage, produces a toxin that causes tissue destruction and kills the shrimp. It does not affect humans. It is transmitted through shrimp populations orally and colonises the gastrointestinal tract.
First reported in China in 2009, EMS/AHPNS has spread across Southeast Asia to Vietnam, Malaysia and Thailand, adversely affecting the industry’s biggest producers. EMS/AHPNS outbreaks typically occur within 30 days of stocking a newly prepared shrimp pond and mortality can exceed 70%. Annual losses to the infection are estimated to exceed US$1 billion.
DETECTION AND TESTING
Fortunately for the industry, visual inspection of shrimp ponds can identify an outbreak of EMS/AHPNS, while research into diagnostic testing methods is ongoing. Typical signs of infection include a darker shell and mottling of the shrimp carapace. Diseased shrimp become lethargic and anorexic. Post mortem pathogen testing can confirm the presence of Vibrio parahaemolyticus. Additionally, on dissection of affected stock the hepatopancreatic organs may appear atrophied and whitish with black streaks.
In Arizona, research continues on the development of diagnostic tests for the EMS/AHPNS pathogen that will enable improved management of hatcheries and ponds, and help lead to a longterm 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.
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 organisation founded
by the Global Aquaculture Alliance (GAA), 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.
Outbreaks have badly affected the industry’s major supplier countries and caused a severe reduction in supplies. As a direct result, prices have reached record levels and secondary supplier countries have been able to benefit from both increased market share and improved revenues.
EMS/AHPNS affects farmed shrimp and the risk of transmission to wild populations by the import of frozen goods into uninfected areas is deemed low. Tests conducted by Arizona University
were unable to transmit the disease from frozen tissue. However, some countries have restricted the import of frozen shrimp and related products from EMS/ AHPNS affected countries.
THE WAY FORWARD
Early detection can minimize losses, but effective diagnostic testing and treatment are not yet available. EMS/AHPNS will be a key topic of discussion at the GAA’s GOAL 2013 Conference in October.
For further information on SGS please visit our Food Safety website.
For more information, please contact:
Ron Wacker, PhD
Global Food Testing Business
t: +49 40 301 012 65