Field and Experimental Evidence of Vibrio parahaemolyticus as the Causative Agent of Acute Hepatopancreatic Necrosis Disease of Cultured Shrimp (Litopenaeus vannamei) in Northwestern Mexico

Abstract

Moribund shrimp affected by acute hepatopancreatic necrosis disease (AHPND) from farms in northwestern Mexico were sampled for bacteriological and histological analysis. Bacterial isolates were molecularly identified as Vibrio parahaemolyticus by the presence of the tlh gene. The tdh-negative, trh-negative, and tlh-positive V. parahaemolyticus strains were further characterized by repetitive extragenic palindromic element-PCR (rep-PCR), and primers AP1, AP2, AP3, and AP and an ems2 IQ2000 detection kit (GeneReach, Taiwan) were used in the diagnostic tests for AHPND. The V. parahaemolyticus strains were used in immersion challenges with shrimp, and farmed and challenged shrimp presented the same clinical and pathological symptoms: lethargy, empty gut, pale and aqueous hepatopancreas, and expanded chromatophores. Using histological analysis and bacterial density count, three stages of AHNPD (initial, acute, and terminal) were identified in the affected shrimp. The pathognomonic lesions indicating severe desquamation of tubular epithelial cells of the hepatopancreas were observed in both challenged and pond-infected shrimp. The results showed that different V. parahaemolyticus strains have different virulences; some of the less virulent strains do not induce 100% mortality, and mortality rates also rise more slowly than they do for the more virulent strains. The virulence of V. parahaemolyticus strains was dose dependent, where the threshold infective density was 10 4 CFU ml ؊1 ; below that density, no mortality was observed. The AP3 primer set had the best sensitivity and specificity. Field and experimental results showed that the V. parahaemolyticus strain that causes AHPND acts as a primary pathogen for shrimp in Mexico compared with the V. parahaemolyticus strains reported to date.

The opportunistic marine pathogen Vibrio parahaemolyticus becomes virulent by acquiring a plasmid that expresses a deadly toxin

“…We note that, before the emergence of AHPND, this binary insecticidal toxin had not been reported in a marine organism to our knowledge. (4,6,18). This has led to the suggestion that the observed necrotic effects are caused by some unidentified toxin (6), and we hypothesized that the secreted form of the pVA1-encoded Pir vp toxin was very likely to be responsible.…”

“…However, it is hard to generalize from this evidence alone because, although all of these strains were isolated from different locations, these locations were all in a single geographic area and lacked geographic diversity. Other reports that have focused on characterizing different AHPND-causing strains have also isolated samples from farms within a single locality (7,18). To properly address this question, a phylogenetic analysis of various AHPND strains with a wide geographic diversity will be necessary.…”

Pathological Changes and Risk Factors of Hepatopancreas Necrosis Disease of Mitten Crab, Eriocheir Sinensis

“…Moreover, HPND also serious impacts on the industry of prawn culture. It was reported that Vibrio parahaemolyticus and Bacillus thuringiensis were involved in HPND of Litopenaeus vannamei [5], and Vibrio parahaemolyticus was the causative agent of acute HPND of cultured Litopenaeus vannamei in Northwestern Mexico [6]. Wu et al reported that simultaneously erupting infection of hepatopancreas baculovirus and vibrios was the main cause of the death of the cultured Penaeus chinensis with HPND [7].…”

Isolation of Bdellovibrio and like organisms and potential to reduce acute hepatopancreatic necrosis disease caused by Vibrio parahaemolyticus

“…In this work, AHPND Vp PSU 5429 at a concentration of 10 7 CFU ml −1 was selected for the assay because investigation of AHPND in a shrimp farm in Mexico revealed that different virulence of V. parahaemo ly ticus depended on bacterial density, and the minimum infective density was 10 4 CFU ml −1 (Soto-Rodriguez et al 2015). In addition, no shrimp mortality was observed at densities below this value, and less virulent strains did not induce 100% mortality.…”