Abstract
Vibrio parahaemolyticus carrying binary toxin genes, pirAB, is one of the etiological agents causing acute hepatopancreatic necrosis disease (AHPND) in shrimp. This disease has emerged recently as a major threat to shrimp aquaculture worldwide. During a routine PCR screening of AHPND-causing V. parahaemolyticus strains, an isolate tested PCR positive for pirB (R13) and another isolate tested positive for both the pirA and pirB (R14) genes. To evaluate the pathogenicity of these isolates, specific pathogen-free (SPF) Penaeus vannamei were experimentally challenged. For both R13 and R14 isolates, the final survival rate was 100% at termination of the challenge, whereas the final survival with the AHPND-causing V. parahaemolyticus was 0%. The nucleotide sequence of the plasmid DNA carrying the binary toxin genes revealed that R13 contains a deletion of the entire pirA gene whereas R14 contains the entire coding regions of both pirA and pirB genes. However, R14 possesses an insertion upstream of the pirA gene. In R14, mRNA for both pirA and pirB genes could be detected but no cognate proteins. This shows that the genome of AHPND-causing V. parahaemolyticus is highly plastic and, therefore, detection of the pirA and pirB genes alone by DNA-PCR is insufficient as a diagnostic test for AHPND.
Highlights
Since 2009, acute hepatopancreatic necrosis disease (AHPND), known as “Early Mortality Syndrome (EMS)”, has caused significant production losses in many South East (SE) Asian countries, including China, Vietnam, Malaysia, Thailand [1,2] and the Philippines [3]
The findings revealed that the genome of V. parahaemolyticus that cause AHPND is highly plastic, and this has implications in the disease manifestation and diagnosis of AHPND in shrimp using PCR-based diagnostic tools
Two V. parahaemolyticus isolates, R13 and R14, originating from a Latin American country that tested positive by PCR for pirB only (R13) or both pirAB (R14), and a human clinical V. parahaemolyticus strain obtained from the American Type Culture Collection (ATCC strain) that does not contain the toxin genes pirAB were used in the bioassay
Summary
Since 2009, acute hepatopancreatic necrosis disease (AHPND), known as “Early Mortality Syndrome (EMS)”, has caused significant production losses in many South East (SE) Asian countries, including China, Vietnam, Malaysia, Thailand [1,2] and the Philippines [3]. There have been some studies that suggest the presence of AHPND in other countries in Central America [6] and South America [7,8]. This emerging disease has caused an estimated loss of USD 15.0 billion in shrimp aquaculture worldwide Due to its rapid spread, AHPND is posing a serious threat to shrimp farming globally
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