Silver nanoparticles induce histopathological alterations in juvenile Penaeus vannamei.

The objective of this study was to evaluate the histopathological alterations in juvenile Penaeus vannamei caused by silver nanoparticles (AgNPs) for two types of experiments: at sublethal concentrations of 3.6 to 7.1 µg/µL of metallic silver (Ag) for a short period up to 72 h and for 2.6 to 7.9 µg of Ag/µL for the long period up to 264 h. The severity degree of the changes was evaluated and the histopathological index (Hi) was determined in both experiments using the necrosis (cellular dead) as an indicator. The pathological changes in the striated muscle, gills, antennal gland, circulatory system, heart, lymphoid organ, and connective tissue are described. The histopathological effects were similar for the two experiments without a direct relationship with the concentrations. In the short-term experiment, the values of Hi were higher (2.34 ± 0.41 at 48 hpi and 1.91 ± 0.39 at 72 hpi) compared with the long-term experiment (values between 0.57 ± 0.36 to 1.74 ± 0.57 at 264 hpi). The observed pathologies are similar to those caused by other metals, with the exception of the agglomerations of black particles in the gills, lymphoid organ, and muscle, which has not been previously reported. This work shows that silver nanoparticles cause damage to shrimp in sublethal concentrations.

Quantitative risk assessment of WSSV transmission through partial harvesting and transport practices for shrimp aquaculture in Mexico.

This quantitative risk assessment provided an analytical framework to estimate white spot syndrome virus (WSSV) transmission risks in the following different scenarios: (1) partial harvest from rearing ponds and (2) post-harvest transportation, assuming that the introduction of contaminated water with viral particles into shrimp culture ponds is the main source of viral transmission risk. Probabilities of infecting shrimp with waterborne WSSV were obtained by approaching the functional form that best fits (likelihood ratio test) published data on the dose-response relationship for WSSV orally inoculated through water into shrimp. Expert opinion defined the ranges for the following uncertain factors: (1) the concentrations of WSSV in the water spilled from the vehicles transporting the infected shrimp, (2) the total volume of these spills, and (3) the dilution into culture ponds. Multiple scenarios were analysed, starting with a viral load (VL) of 1×102mL-1 in the contaminated water spilled that reached the culture pond, whose probability of infection of an individual shrimp (Pi) was negligible (1.7×10-7). Increasing the VL to 1×104.5mL-1 and 1×107mL-1 yielded results into very low (Pi=5.3×10-5) and high risk (Pi=1.6×10-2) categories, respectively. Furthermore, different pond stocking density (SD) scenarios (20 and 30 post-larvae [PL]/m2) were evaluated, and the probability of infection of at least one out of the total number of shrimp exposed (PN) was derived; for the scenarios with a low VL (1×102mL-1), the PN remained at a negligible risk level (PN, 2.4×10-7 to 1.8×10-6). For most of the scenarios with the moderate VL (1×104.5mL-1), the PN scaled up to a low risk category (PN, 1.1×10-4 to 5.6×10-4), whereas for the scenarios with a high VL (1×107mL-1), the risk levels were high (PN, 2.3×10-2 to 3.5×10-2) or very high (PN, 1.1×10-1 to 1.6×10-1) depending on the volume of contaminated water spilled in the culture pond (VCWSCP, 4 or 20L). In the sensitivity analysis, for a SD of 30 PL/m2, it was shown that starting with a VL of 1×105mL-1 and a VCWSCP of 12L, the PN was moderate (1.05×10-3). This was the threshold for greater risks, given the increase in either the VCWSCP or VL. These findings supported recommendations to prevent WSSV spread through more controlled transportation and partial harvesting practices.

Genotyping WSSV isolates from northwestern Mexican shrimp farms affected by white spot disease outbreaks in 2010-2012.

White spot disease (WSD) causes high mortality in cultured shrimp throughout the world. Its etiologic agent is the white spot syndrome virus (WSSV). The genomic repeat regions ORF 75, ORF 94, and ORF 125 have been used to classify WSSV isolates in epidemiological studies using PCR with specific primers and sequencing. The present study investigated the variation in nucleotide sequences from 107, 150, and 143 isolates of WSSV collected from Litopenaeus vannamei shrimp ponds with WSD outbreaks in northwestern Mexico during the period 2010-2012, in the genomic repeat regions ORFs 75, 94, and 125, respectively. The haplotypic nomenclature for each isolate was based on the number of repeat units and the position of single nucleotide polymorphisms on each ORF. We report finding 17, 43, and 66 haplotypes of ORFs 75, 94, and 125, respectively. The study found high haplotypic diversity in WSSV using the complete sequences of ORFs 94 and 125 as independent variables, but low haplotypic diversity for ORF 75. Different haplotypes of WSSV were found from region-to-region and year-to-year, though some individual haplotypes were found in different places and in more than one growing cycle. While these results suggest a high rate of mutation of the viral genome at these loci, or perhaps the introduction of new viral strains into the area, they are useful as a tool for epidemiological surveys. Two haplotypes from some of the ORFs in the same shrimp were encountered, suggesting the possibility of multiple infections.