Quantitation of infectious myonecrosis virus in different tissues of naturally infected Pacific white shrimp, Litopenaeus vannamei, using real-time PCR with SYBR Green chemistry

Identification of SNPs potentially related to immune responses and growth performance in Litopenaeus vannamei by RNA-seq analyses

Litopenaeus vannamei is one of the most important shrimp species for worldwide aquaculture. Despite this, little genomic information is available for this penaeid and other closely related taxonomic crustaceans. Consequently, genes, proteins and their respective polymorphisms are poorly known for these species. In this work, we used the RNA sequencing technology (RNA-seq) in L. vannamei shrimp evaluated for growth performance, and exposed to the White Spot Syndrome Virus (WSSV), in order to investigate the presence of Single Nucleotide Polymorphisms (SNPs) within genes related to innate immunity and growth, both features of great interest for aquaculture activity. We analyzed individuals with higher and lower growth rates; and infected (unhealthy) and non-infected (healthy), after exposure to WSSV. Approximately 7,000 SNPs were detected in the samples evaluated for growth, being 3,186 and 3,978 exclusive for individuals with higher and lower growth rates, respectively. In the animals exposed to WSSV we found about 16,300 unique SNPs, in which 9,338 were specific to non-infected shrimp, and 7,008 were exclusive to individuals infected with WSSV and symptomatic. In total, we describe 4,312 unigenes containing SNPs. About 60% of these unigenes returned GO blastX hits for Biological Process, Molecular Function and Cellular Component ontologies. We identified 512 KEGG unique KOs distributed among 275 pathways, elucidating the majority of metabolism roles related to high protein metabolism, growth and immunity. These polymorphisms are all located in coding regions, and certainly can be applied in further studies involving phenotype expression of complex traits, such as growth and immunity. Overall, the set of variants raised herein enriches the genomic databases available for shrimp, given that SNPs originated from nextgen are still rare for this relevant crustacean group, despite their huge potential of use in genomic selection approaches.

Artemia franciscana as a vector for infectious myonecrosis virus (IMNV) to Litopenaeus vannamei juvenile

In 2004, the infectious myonecrosis virus (IMNV) was recognized as the main cause of Litopenaeusvannamei shrimp culture's drop in Brazil. In health animal control programs, in order to reduce virus prevalence in production units it is necessary to screen live feed used. Among live diets used in aquaculture, the brine shrimp Artemia sp. is essential in crustacean larviculture and maturation. The aim of the present study was to investigate the susceptibility of Artemiafranciscana to IMNV through an immersion challenge and virus-phytoplankton adhesion route and to elucidate its role as a vector for IMNV transmission to L.vannamei. A. franciscana adults were infected with IMNV through both routes, as demonstrated by PCR-positive reactions. However, infected A. franciscana showed no signs of infection. More than 40% of L. vannamei juveniles fed with IMNV-infected A. franciscana by virus-phytoplankton adhesion route were positive by real-time PCR, whereas only a 10% infection rate was found among shrimp fed with IMNV-infected brine shrimp using the immersion challenge. Significant differences were found in mean viral load between immersion and virus-phytoplankton adhesion shrimp treatments (p ⩽ 0.05). Moreover, the mean viral loads were 1.34 × 10(2) and 1.48 × 10(4) copies/μg(-1) of total RNA for virus-phytoplankton adhesion and IMNV-infected tissue treatments, respectively, and the difference was not significant (p ⩾ 0.05). The results indicated that A. franciscana act as a vector for IMNV transmission under the experimental conditions examined. Although no mass mortalities were detected in L. vannamei fed with IMNV-infected brine shrimp, these infected shrimp should not be disregarded as a source of IMNV in grow-out units.

A real-time PCR for the detection of infectious myonecrosis virus in penaeid shrimp

Infectious myonecrosis virus (IMNV) is a recently observed shrimp virus, which threats the cultured Litopenaeus vannamei and can cause huge economic loss in shrimp farming industry. The specific aim of this study was to develop a new sensitive real-time PCR method for the specific detection of shrimp IMNV. A real-time PCR assay with a pair of primers to specifically amplify a 101bp IMNV cDNA fragment and a corresponding TaqMan probe was developed, which shown to be specific for IMNV without cross reaction with DNA samples prepared from four other shrimp viruses including white spot syndrome virus (WSSV), hepatopancreatic parvovirus (HPV), monodon baculovirus (MBV), and infectious hypodermal and haematopoietic virus (IHHNV). The method could detect as low as one single copy of IMNV plasmid cDNA.