Determination, Characterization, and Control Measures of the Agent Causing Early Mortality Syndrome (EMS) also known as Acute Hepatopancreatic Necrosis Syndrome (AHPNS) in Farmed Penaeid Shrimp

Abstract

A series of studies were conducted on an emerging disease in farmed penaeid shrimp. This disease was first named as Early Mortality Syndrome (EMS) or more descriptively as Acute Hepatopancreatic Necrosis Syndrome (AHPNS). As part of the outcome of this research, the etiology of EMS/AHPNS was demonstrated. EMS was first classified as an idiopathic disease because no causative agent had been identified. Preliminary studies conducted in Vietnam in 2012 by the University of Arizona Aquaculture Pathology Laboratory (UAZ-APL) indicated that EMS is infectious (Tran et al., 2013). The agent was identified as a unique strain of Vibrio parahaemolyticus. Hence, EMS has a bacterial etiology confirmed by satisfying Koch's Postulates. Further studies focusing on the bacterial isolate causing EMS revealed that the agent could produce toxin(s), which is responsible for the primary pathology in affected shrimp. Since the causative agent has been identified, we propose a new name for EMS as Acute Hepatopancreatic Necrosis Disease (AHPND). Characterizations of the AHPND-causing Vibrio parahaemolyticus: Biochemical methods and molecular methods were used. Based on these results, various diagnostic methods were developed including polymerase chain reaction (PCR) test and biochemical tests. Other aspects of the AHPND causing V. parahaemolyticus were also run to determine such as antibiogram and the development of resistance mechanism of the bacteria exposed to farm conditions with antibiotic medications, pathogenicity, and infection dose of the bacteria, mode of infection, mechanisms governing the toxin production, and effects of environmental parameters on the invasion of the agent. Some proposed control measures for AHPND: Several antibiotic-free approaches were tested to determine viable control methods for AHPND. The principle proposed control method is to increase biosecurity. With the PCR method that has been developed, potential sources of the pathogen such as post-larvae and broodstock can be tested. As more and more insights of the pathogen were explored, the behavior of the pathogen was further elucidated. Based on this, control methods such as using polyculture with tilapia, probiotics, and bioflocs system were also tested. Several improvements in shrimp farming practices that may reduce the outbreak of the disease were also proposed.