Download AHPNS aetiology – announcement May 2013

Global Aquaculture Alliance
http://www.gaalliance.org/newsroom/news.php?Cause-Of-EMS-Shrimp-Disease-Identified-107
Cause Of EMS Shrimp Disease Identified
May, 2013
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.