The Thai Department of Fisheries (DOF), 2013 estimated that outbreaks of acute early mortality (often called
early mortality syndrome or EMS) in cultivated shrimp were responsible for a 33% drop in shrimp production
during thefirst quarter of 2013. Similar early mortality in Vietnam was ascribed to specific isolates ofVibrio
parahaemolyticusthat caused acute hepatopancreatic necrosis disease (AHPND) but the status of EMS/AHPND
in Thailand was unclear. Here we describe the isolation and characterization of bacteria isolated from the hepa-topancreas (HP) of shrimp collected from an early mortality outbreak farm in Thailand. Four independent bacte-rial isolates were identified asV. parahaemolyticusby BLAST analysis and by gene-specific marker detection of a
lecithin dependent hemolysin (LDH) considered to be specific for the species. Immersion challenges with 3 of
these and a reference isolate, obtained from China in 2010, using a previously published laboratory infection
model caused very high mortality accompanied by characteristic AHPND histopathology in the shrimp HP.
Tests with one of these isolates (5HP) revealed that rate of mortality was dose dependent. Using the same chal-lenge protocol, the 4th isolate (2HP) also caused high mortality, but it was not accompanied by AHPND histopa-thology. Instead, it caused a different histopathology of the HP including collapsed epithelia and unique
vacuolization of embryonic cells (E-cells). These results revealed the possibility of diversity in isolates of
V. parahaemolyticusthat may cause early mortality in shrimp cultivation ponds. Genomic and episomic DNA of
these isolates and isolates ofV. parahaemolyticusthat cause no disease need to be compared tobetter understand
the molecular basis of bacterial virulence in AHPND.
The Thai Department of Fisheries (DOF), 2013 estimated that outbreaks of acute early mortality (often called
early mortality syndrome or EMS) in cultivated shrimp were responsible for a 33% drop in shrimp production
during thefirst quarter of 2013. Similar early mortality in Vietnam was ascribed to specific isolates ofVibrio
parahaemolyticusthat caused acute hepatopancreatic necrosis disease (AHPND) but the status of EMS/AHPND
in Thailand was unclear. Here we describe the isolation and characterization of bacteria isolated from the hepa-topancreas (HP) of shrimp collected from an early mortality outbreak farm in Thailand. Four independent bacte-rial isolates were identified asV. parahaemolyticusby BLAST analysis and by gene-specific marker detection of a
lecithin dependent hemolysin (LDH) considered to be specific for the species. Immersion challenges with 3 of
these and a reference isolate, obtained from China in 2010, using a previously published laboratory infection
model caused very high mortality accompanied by characteristic AHPND histopathology in the shrimp HP.
Tests with one of these isolates (5HP) revealed that rate of mortality was dose dependent. Using the same chal-lenge protocol, the 4th isolate (2HP) also caused high mortality, but it was not accompanied by AHPND histopa-thology. Instead, it caused a different histopathology of the HP including collapsed epithelia and unique
vacuolization of embryonic cells (E-cells). These results revealed the possibility of diversity in isolates of
V. parahaemolyticusthat may cause early mortality in shrimp cultivation ponds. Genomic and episomic DNA of
these isolates and isolates ofV. parahaemolyticusthat cause no disease need to be compared tobetter understand
the molecular basis of bacterial virulence in AHPND.
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