Experimental method to detect the cause of EMS
In early 2009, a new symptom appeared in both giant tiger shrimp and white shrimp, called early mortality syndrome (EMS), which caused major damage to shrimp farms in the south. China. In 2010, EMS appeared in many shrimp farming areas in southern Vietnam and spread to other countries such as Malaysia in 2011 and Thailand in 2012.
In 2011, based on acute lesions of premature death syndrome, a new name was proposed as “Acute Hepatopancreatic Necrosis Syndrome” (AHPNS). By the beginning of 2013, the University of Arizona’s aquaculture laboratory has isolated the purebred line of EMS.
AHPNS usually occurs within 20-30 days after stocking. The disease occurs in two stages, the external signs in the early stage usually see pancreatic hepatic light color, the hepatic pancreatic size shrink to 50% and in the late stage, the liver may appear black in the pancreas due to the black spots. melaninization of blood cells in the hematoma in the pancreas. The mortality rate can be as high as 100% for several days after the onset of the disease.
Histopathological analysis of shrimp infected with AHPNS showed that necrotic pancreatic necrosis progressed from the inside out with functional impairment of pancreatic liver epithelial cells. These epithelial cells peel off the walls of the hepatopancreas and get necrotic. In the late stage, many bacteria appear in the hepatopancreas of the shrimp, the connective tissue in the pancreas is light color, difficult to crush because of the thorns, there are secondary inflammatory bacteria attack. This type of lesion shows that the AHPNS lesion on the hepatopancreas was originally caused by toxins.
Transmission experiment performed at the University of Arizona
Drainage and analgesic techniques are used for the experiments. Conducted 3 independent experiments.
Experiment 1 was used to confirm the results of bacteriological experiments with bacterial blends of shrimp stomach and immersion method.
Experiment 2 was conducted with bacterial strains isolated from a bacterial mixture of shrimp stomach.
Experiment 3 was conducted with the purebred strains of the pathogenic bacteria from experiment 2 and analgesia technique with cultured bacterial cultures and sterile filter media.
The results of the above experiments showed that immersion experiments with bacterial blends from the stomach showed that infected shrimp infected and died in series, histopathological analysis showed that the lesions on shrimp experiments completely Shrimp infected shrimp collected from ponds in Vietnam. A pure strain of bacteria isolated from shrimp gastric mucus mixture also causes typical lesions of shrimp infected with AHPNS.
Flaking cells form the source of the attack. It spreads through the oral cavity, locates in the gastrointestinal tract, then produces virulent damage to the hepatopancreas.
From February to March 2013, the pathogen was analyzed and confirmed as belonging to the Vibrio harveyi and most closely related to Vibrio parahaemolyticus.
Although the cause of the disease has been identified, it is not yet possible to find effective remedies.
There are many ideas that can use molasses because Vibrio parahaemolyticus bacteria can not use sugar cane. Can be mixed with tilapia or mixed with seaweed, fish and shrimp.
Future studies will clarify the role of bacteriophage in the potential for virulence or virulence of bacteria causing AHPNS. Numerous studies to control AHPNS are currently being studied at the University of Arizona.
Consumer health issues and biosafety
Some rare strains of Vibrio parahaemolyticus have the ability to carry genes that cause haemorrhage and intestinal disease in infected fish. Fortunately, this strain of AHPNS does not carry the same genes and does not produce toxins that cause food poisoning in humans. Germs in shrimp are inactivated when frozen and thawed.
Source: Le Hai Quynh (Collected from EMS workshop at Ho Chi Minh City University of Agriculture and Forestry on June 28, 2013)