White Spot Syndrome Virus Infected Shrimp Research Articles

Long noncoding RNA profiling in hepatopancreas of Pacific white shrimp and its role in response to white spot syndrome virus infection

Long noncoding RNA (lncRNA) is a potential regulator of biological processes, including immunity, reproduction, and development. Although several transcriptome studies have focused on responses of viral infections in several organisms, the role of lncRNAs in viral responses in shrimp is still unclear. Therefore, this work aimed to identify putative lncRNAs and study their role in white spot syndrome virus (WSSV) infection in white shrimp. The hepatopancreas transcriptome from WSSV infected shrimp was analyzed in silico to identify putative lncRNAs. Among 221,347 unigenes of the de novo assembled transcriptome, 44,539 putative lncRNAs were identified, 32 of which were differentially expressed between WSSV-infected and control shrimp. Five candidate lncRNAs were validated for their expressions in shrimp tissues and in response to WSSV infection. Lnc164 was chosen for further investigation of its role in WSSV infection. Knockdown of lnc164 prolonged survival of shrimp when challenged with WSSV, suggesting a role in shrimp immunity. In addition, lnc164 was not directly involved in the control of total hemocytes and viral loads in hemolymph of WSSV-infected shrimp. A set of lnc164-regulated genes was obtained by RNA sequencing among which 251 transcripts were differentially expressed between lnc164 knockdown and control shrimp. Six immune-related genes were validated for their expression profiles. Our work sheds light on lncRNA profiles in L. vannamei in response to WSSV infection and paves the way to a functional study of lnc164 in host antiviral response.

Use of Sonneratia alba leaf extract solution for White Spot Syndrome Virus prevention in tiger shrimp postlarvae

White Spot Syndrome Virus (WSSV) is one of the leading causes of mass mortality in tiger shrimp culture. The objective of this study was to determine the impact of different immersion times in 1% Sonneratia alba extract on the ability of WSSV infected tiger shrimp to survive as post-larvae. Eight treatments were used in this study, with three replications for each. The treatments were as follows: A) 12 hours of immersion; B) 24; C) 36; D) 48; E) 60; F) 72; G) Positive control (infected with WSSV but without mangrove extract); and H) Negative control (without WSSV infection and mangrove extract). with three replications in each treatment. Tiger prawn post-larvae were stocked at a density of 20 squares per jar. At a rate of 20% of the daily biomass, they were being fed three times per day. Tiger shrimp post-larvae mortality was examined every day for eight days. At the beginning and conclusion of the study, analyses of water quality such as Total Organic Matter, NH3-N, and NO2-N, were made. The findings revealed that treatment F seemed to have the best survival rate (85.0%) and positive control had the lowest survival rate (0%). (treatment G). The shrimp were more resistant to WSSV due to the longer immersion in the herbal extracts.

Effect of Brachionus plicatilis and Navicula sp. on Pacific white shrimp growth performance, Vibrio, immunological responses and resistance to white spot virus (WSSV) in nursery biofloc system

The purpose of this study was to evaluate the effect of Brachionus plicatilis and Navicula sp. addition on growth performance, Vibrio count, immunological responses and resistance to white spot syndrome virus (WSSV) of Litopenaeus vannamei in nursery biofloc system. The study was divided into two phases and four treatments were examined in the first phase: BFT (biofloc); BFT-N (addition of 10×104 cells mL−1 of Navicula sp.); BFT-B (addition of 30 org mL−1 of B. plicatilis) and; BFT-BN (addition of 10×104 cells mL−1 of Navicula sp. and 30 org mL−1 of B. plicatilis), all in triplicate and; the second phase included a viral challenge, also in triplicate. Shrimp (PL10, 2 ± 0,01 mg) were reared in biofloc system (fertilized with inorganic and anaerobic and aerobic carbon process with a microbial mix), for 45 days at a density of 3000 shrimp m-3, with controlled temperature, without water exchange and fed with commercial feed. The diatoms and rotifers were added every 10 days, and at the end, shrimp performance, water quality, Vibrio count and total hemocyte count were evaluated. After 45 days, 300 shrimp m−3 were challenged with WSSV (2.2 × 107 copies of WSSV μL−1 of DNA) for 9 days. The BFT-N, BFT-B and BFT-BN treatments had higher values of final weight (1.02 to 1.16 g) and yield (2.85 to 3.30 kg m−3) which were higher than the BFT (0.86 g and 2.46 kg m−3). There were no differences in water quality among treatments. Vibrio count from water samples was significantly lower at the end of experiment with significant decrease of non-sucrose-fermenting gram-negative bacteria. However, for hepatopancreas, the Vibrio count was significant higher at the end, however with significantly increase of sucrose-fermenting gram-negative bacteria (98 to 100%). There was no significant difference between the THC and hyalyne count for all treatments. Massive mortality rate was firstly achieved in BFT and BFT-B treatments in the second phase. However, all treatments reported complete mortality and WSSV infection was confirmed by nested-PCR and histopathologically, with lesions suggestive of WSD (presence of nodules and tissue deformations). The Navicula sp. and B. plicatilis addition contributed to better performance parameters of shrimp in the nursery biofloc system, although there was no significant effect on the WSSV resistance of shrimp. Absence of tissue degeneration in WSSV infected shrimp from BFT-N treatment indicated benefit of using diatoms under standardized conditions.

Multiplex-PCR protocol development for rapid screening of white spot syndrome virus (WSSV) in shrimp

This study was aimed to develop a faster single step multiplex PCR protocol for the simultaneous detection of white spot syndrome virus (WSSV) with its host (i.e. shrimp) as internal positive control. To do so, four combinations of primer were tested (I. 16S rRNA+Lo F1R1; II. 16S rRNA+Lo F2R2; III. 16S rRNA+Lo F1R2; IV. 16S rRNA+Lo F2R1) which were selected based on two pairs of WSSV specific primer (Lo F1R1 and Lo F2R2) and one pair of shrimp specific primer (16S rRNA). DNA extracted from WSSV infected shrimp were amplified by PCR in a single tube using each of the primer combinations and the thermal cycling conditions as well as reagent compositions were optimized. All the primer combinations yielded their expected band sizes with stronger band resolution intensity that indicated the development of four multiplex PCR protocols. The developed multiplex protocols reduced the chance of cross contamination and these were found to be faster, single step and unique with less effort and resource use. Considering sensitivity and specificity, among the protocols, we suggested the protocols based on 16S rRNA+Lo F1R1 and/or 16S rRNA+Lo F2R2 primer combinations for rapid and routine screening of WSSV in shrimp PL, juvenile and adult.

ISOLATION OF WHITE SPOT SYNDROME VIRUS (WSSV) IN EGYPTIAN SHRIMP USING CONVENTIONAL PCR AND REAL TIME PCR (QPCR) TECHNIQUES

Shrimp aquaculture industry threated by high mortality rates and severe economic losses as a result of white spot syndrome virus (WSSV) infection. Early-screening and diagnosis of WSSV are great strategies to decrease the economic losses of the disease on shrimp aquaculture. Therefore, this study was carried out to detect of white WSSV infected shrimp under using two molecular based methods, conventional PCR and qPCR. A total number of 90 samples of red (Aristeus antennatus) and gray (Penaeus latisclcatus) shrimp were collected from Kafr El-Sheikh and Alexandria governorates. External examination of shrimps collected from Kafr El-Sheikh Governorate revealed typical WSSV clinical signs (including loose and easily detached cuticle with appearance of small white spots (3 mm in diameter) and /or larger patches in the external surface of carapace and cephalothorax. The internal examination showed yellowish white, fragile and swollen hepatopancreas and swollen or shrunken lymphoid tissue. Red shrimp showed slightly obvious white spots without any internal lesions. PCR results confirmed the clinical investigation and postmortem (PM) examination and revealed presence of WSSV partial sequences with a size of 190 bp in shrimp samples from Kafr El-Sheikh Governorate. In contrast, samples collected from Alexandria (Borg El-Arab) gave negative results. The result of qPCR confirmed that obtained by conventional PCR and showed that all positive results of WSSV by conventional PCR gave cycle threshold (Ct) values ranged from 34.81 to 40.06. Our results concluded that, WSSV Diseases of shrimp attack shrimp markets of Kafr El-Sheikh Governorate. The conventional PCR and qPCR based methods for isolation and identification of shrimp WSSV, provided accurate results.Key words: WSSV; PCR; qPCR; shrimp

Litopenaeus vannamei attenuates white spot syndrome virus replication by specific antiviral peptides generated from hemocyanin

Recent studies have shown that hemocyanin plays immune-related functions apart from its canonical respiratory function. While shrimp hemocyanin is found to generate antimicrobial peptides, antiviral related peptides have not been reported. In the present study, the serum of white spot syndrome virus (WSSV) infected Litopenaeus vannamei analyzed by two-dimensional gel electrophoresis, revealed 45 consistently down-regulated protein spots and 10 up-regulated protein spots. Five of the significantly up-regulated spots were identified as hemocyanin derived peptides. One of the five peptides, designated LvHcL48, was further characterized by analyzing its primary sequence via Edman N-terminal sequencing, C-terminal sequencing and amino acid sequence alignment. LvHcL48 was found to be a 79 amino acid fragment (aa584-662) from the C-terminal domain of L. vannamei hemocyanin protein (ADZ15149). Both in vivo and in vitro functional studies revealed that LvHcL48 has immunological activities, as recombinant LvHcL48 protein (rLvHcL48) significantly inhibited the transcription of the WSSV genes wsv069 and wsv421 coupled with a significant reduction in WSSV copy numbers. Further analysis showed that LvHcL48 could interact with the WSSV envelope protein 28 (VP28). Our present data therefore reveals the generation of an antiviral hemocyanin derived peptide LvHcL48 from WSSV infected shrimp, which binds to the envelope protein VP28 of WSSV.

Assessment of the origin of white spot syndrome virus DNA sequences in farmed Penaeus monodon in Australia

Until 2016, the Australian shrimp industry was considered free of White Spot Syndrome Virus (WSSV), a destructive pathogen responsible for the huge economic losses in the shrimp culture industry in most shrimp producing countries worldwide. In December 2016, there was an outbreak of WSSV in commercial Penaeus monodon shrimp farms located on the Logan River in Queensland, northeast Australia which resulted in the loss of all shrimp production on the Logan river either directly from the virus itself or indirectly through destruction of the shrimp production as part of quarantine measures.The first objective of this study was to consider the possible origins of the outbreak, whether the WSSV outbreak arose of an exotic introduction or a local endemic strain. The Australian WSSV DNA sequences, from nine farmed samples, amplified using the 146F2R2 primers spanning relatively conserved regions, were identical to each other and had very close identity to overseas WSSV strains which did not refute the working hypothesis that the outbreak was caused by an invasive species from overseas rather than from entry into aquaculture of a long term Australian endemic strain.The second objective was to consider the possible source of the outbreak (i.e. country or region). To do this, highly variable genomic WSSV regions were identified and novel primers designed for this study to amplify variable genomic regions so it would be possible to conduct DNA sequence comparisons, theoretically, from a hundreds of samples in a relatively short period of time and low cost, something not readily possible with full genomic sequencing. In practice we generated DNA sequences using up to five of these novel primers (and the published ORF 125 variable primers) from three Australian farmed shrimp samples, from two farmed Vietnamese samples (from the north and south of the country), one retail product from Vietnam and one retail product from China sold in Australia and compared these sequences to 10 published overseas WSSV genomes. Available data indicated the Australian sequences were most similar to published sequences from China, and less closely related to sequences from other regions, for example sequences we derived from Vietnamese farmed samples.The third objective was to assess possible physical routes of infection into Australia by testing for the presence of WSSV DNA in aquaculture feed samples used at the time of the outbreak and in imported shrimp retail items. No PCR positives were detected from two samples of shrimp feeds used at the time of the outbreak. Nearly every Australian retail item of imported shrimp product (12 out of 13) tested positive for WSSV and DNA sequences could be obtained from the amplified PCR products indicating that at some point in their history, nearly all the imported samples were in contact with WSSV.In conclusion, our data, considered together, are consistent with the following hypotheses: an exotic shrimp virus, WSSV, which is of considerable economic importance, has breached Australia's biosecurity; the Australian WSSV strain is mostly closely related to one reported from Asia; a plausible physical route of entry may have been through the importation of WSSV infected shrimp for retail sale.

Investigation and confirmation of white spot syndrome virus (WSSV) infection in wild caught penaeid shrimps of Andaman and Nicobar Islands, India.

White spot syndrome virus (WSSV) is one of the most prevalent, widespread and devastating pathogen associated with shrimp population. The present study was aimed at screening the wild caught shrimps from Andaman and Nicobar Islands (ANI) for WSSV infection. Shrimp samples of different penaeid species including Penaeus monodon, Penaeus indicus, Penaeus merguiensis and Metapenaeus monoceros collected from nine different landing centers across the coast of ANI were screened for WSSV infection. Presence of white spots, a typical clinical sign of white spot disease was observed on the exoskeleton of WSSV infected shrimp samples. Out of 241 shrimp samples, 39 samples of P. monodon were found positive for WSSV by nested PCR. Histopathological examination revealed eosinophilic to basophilic intranuclear inclusion bodies in gill tissue which are typical characteristics of WSSV infection. Nucleotide sequence of WSSV isolated from ANI showed 100% identity to the sequences of WSSV reported from Thailand, Taiwan, China, Egypt, Mexico, Korea, France and 99% identity to WSSV reported from India. The detection of WSSV in wild P. monodon of ANI further confirms the virus spread and biogeography.

Pathogenicity of white-spot syndrome virus in Macrobrachium nipponensis via different infection routes

Macrobrachium nipponensis is delicious and has high economic value, but its susceptibility to white-spot syndrome virus (WSSV) is unknown. Susceptibility, morbidity, and multiplication of WSSV in M. nipponense were studied by epidemiological survey, infection experiment and qPCR. M. nipponense was the natural host of WSSV, and the natural carrying rate was about 8.33%. M. nipponense could be infected with WSSV via oral administration, muscle injection and immersion, and the cumulative infection rate of 10 d exposure was 100%, and the cumulative mortality rates were 100%, 75% and 0%, respectively. The infection of WSSV is fast by muscle injection. The virus content after 5 day's injection is 1 000 times higher than that of the first day of infection, and the mortality rate reached 100% after 8 days. The median lethal dose (LD₅₀) measured as the mortality of infected M. nipponense via injection indicated the LD₅₀ in the concentration of WSSV of 2.71×10⁵ virions/μL. In shrimp farming, M. nipponense can be infected by ingesting WSSV infected shrimp or dead shrimp, and also by soaking in WSSV-containing water and thus become a vector, consequently affecting the spread and pathogenicity of WSSV.

Litopenaeus vannamei clathrin coat AP17 involved in white spot syndrome virus infection.

White spot syndrome virus (WSSV) is the main pathogen of shrimp culture, and has brought great losses of the shrimp aquaculture industry every year since it has been found. However, the specific mechanism of the virus into the cell is not very clear. Recent research suggests that clathrin-mediated endocytosis is involved in WSSV infection. By sequence analysis, clathrin coat AP17 is an σ subunit of AP-2 complex which is involved in clathrin-mediated endocytosis. To obtain the full-length sequence of Clathrin coat AP17 of Litopenaeus vannamei (LvCCAP17), the rapid amplification of cDNA ends (RACE) was performed to get the sequence of 3'and 5' end and splicing by DNAMAN. The full-length sequence of LvCCAP17 is 842 bp and expected to encoding 142 amino acids, and the amino acid sequence was analyzed by online software. The mRNA expression of LvCCAP17 in different tissues was carried out with quantitative real-time PCR and the LvCCAP17 was detected in all tested tissues of Litopenaeus vannamei. The transcriptional expression level of LvCCAP17 in epithelium and hepatopancreas was significantly up-regulated after WSSV infection. Far-Western blotting and ELISA assay showed that LvCCAP17 interacted with rVP26 and rVP37. Silencing of LvCCAP17 gene by double-strand RNA (dsRNA) interference significantly delay of cumulative mortality rate in WSSV infected shrimp and reduced the expression level of immediate early gene 1(ie1) and vp28. These results indicated that clathrin-meated endocytosis is responsible for WSSV infection.

Gene expression profiling in gill tissues of White spot syndrome virus infected black tiger shrimp Penaeus monodon by DNA microarray.

White spot syndrome virus (WSSV) continues to be the most devastating viral pathogen infecting penaeid shrimp the world over. The genome of WSSV has been deciphered and characterized from three geographical isolates and significant progress has been made in developing various molecular diagnostic methods to detect the virus. However, the information on host immune gene response to WSSV pathogenesis is limited. Microarray analysis was carried out as an approach to analyse the gene expression in black tiger shrimp Penaeus monodon in response to WSSV infection. Gill tissues collected from the WSSV infected shrimp at 6, 24, 48h and moribund stage were analysed for differential gene expression. Shrimp cDNAs of 40,059 unique sequences were considered for designing the microarray chip. The Cy3-labeled cRNA derived from healthy and WSSV-infected shrimp was subjected to hybridization with all the DNA spots in the microarray which revealed 8,633 and 11,147 as up- and down-regulated genes respectively at different time intervals post infection. The altered expression of these numerous genes represented diverse functions such as immune response, osmoregulation, apoptosis, nucleic acid binding, energy and metabolism, signal transduction, stress response and molting. The changes in gene expression profiles observed by microarray analysis provides molecular insights and framework of genes which are up- and down-regulated at different time intervals during WSSV infection in shrimp. The microarray data was validated by Real Time analysis of four differentially expressed genes involved in apoptosis (translationally controlled tumor protein, inhibitor of apoptosis protein, ubiquitin conjugated enzyme E2 and caspase) for gene expression levels. The role of apoptosis related genes in WSSV infected shrimp is discussed herein.

Transcript Analysis of White spot syndrome virus Latency and Phagocytosis Activating Protein Genes in Infected Shrimp (Penaeus monodon)

Viral latency has been recently observed to be associated with White spot syndrome virus (WSSV) infection in shrimp. In the present study, shrimp samples (Penaeus monodon) surviving WSSV infection were examined for presence of WSSV in latent phase. Virus latency was observed in shrimp which were either experimentally challenged with WSSV and survived the infection or those which survived the natural infection. Three viral transcripts (ORFs 427, 151, 366) associated with latency were analyzed by real-time PCR. The shrimp surviving the natural WSSV infection on estimation with RT-PCR were found to have low grade of WSSV infection (less than 56 copies of WSSV). All the shrimp samples were RT-PCR negative for structural protein genes of WSSV, VP24 and VP28, indicating that these samples were harboring latent phase virus. RT-PCR of all the shrimp samples which survived WSSV infection revealed amplification of phagocytosis activating protein (PAP) gene (435bp) with higher gene expression levels in experimentally challenged shrimp when compared to naturally infected shrimp. The expression of PAP in WSSV infected shrimp samples indicates its possible role in host response for resistance against WSSV infection. PAP was cloned and expressed as recombinant protein for protection studies. Shrimp were injected with three doses (5, 15 and 20μgg(-1) body weight) of recombinant PAP. Relative percent survival of 10% was observed in shrimp immunized with the dose of 15μgg(-1) body weight of recombinant PAP. The expression of both WSSV latency associated and PAP genes obtained from shrimp surviving the WSSV infection, indicates the possible role of these genes in host-pathogen interaction.

Gene expression and protein levels of thioredoxin in the gills from the whiteleg shrimp (Litopenaeus vannamei) infected with two different viruses: The WSSV or IHHNV

The thioredoxin (TRX) system in crustaceans has demonstrated to act as a cell antioxidant being part of the immune response by dealing with the increased production of reactive oxygen species during bacterial or viral infection. Since the number of marine viruses has increased in the last years significantly affecting aquaculture practices of penaeids, and due to the adverse impact on wild and cultured shrimp populations, it is important to elucidate the dynamics of the shrimp response to viral infections. The role of Litopenaeus vannamei thioredoxin (LvTRX) was compared at both, mRNA and protein levels, in response to two viruses, the white spot syndrome virus (WSSV) and the infectious hypodermal and hematopoietic necrosis virus (IHHNV). The results confirmed changes in the TRX gene expression levels of WSSV-infected shrimp, but also demonstrated a more conspicuous response of TRX to WSSV than to IHHNV. While both the dimeric and monomeric forms of LvTRX were detected by Western blot analysis during the WSSV infection, the dimer on its reduced form was only detected through the IHHNV infectious process. These findings indicate that WSSV or IHHNV infected shrimp may induce a differential response of the LvTRX protein.

Hematological changes in white spot syndrome virus-infected shrimp, Fenneropenaeus chinensis (Osbeck)

The pathological changes of hemocytes in the haemolymph and hepatopancreas were examined in experimentally and naturally WSSV (white spot syndrome virus) infected Fenneropenaeus chinensis. The results showed that the pathological manifestations of hemocytes were similar among moribund shrimps infected via injection, feeding and by nature. Firstly, the total hemocyte counts (THCs) in WSSV-infected shrimp were significantly lower than those in healthy shrimp. Secondly, necrotic, broken and disintegrated cells were often observed, and a typical hematolysis was present in the haemolymph smear of WSSV-infected shrimp. Thirdly, necrosis and typical apoptosis of hemocytes were detected with TEM in the peripheral haemolymph of WSSV-infected shrimp. Hyalinocytes and semi-granulocytes with masses of WSSVs in their nuclei often appeared, whereas no granular hemocytes with WSSV were found in the hepatopancreas of moribund infected shrimps. All our results supported that hemocytes were the main target cells of WSSV, and hyalinocytes and semigranular hemocytes seemed to be more favorable for WSSV infection in F. chinensis.

Protein expression in white spot syndrome virus infected Penaeus monodon fabricius

White spot syndrome virus (WSSV) is the causative agent of the white spot disease of shrimp. Penaeus monodon were captured from Muttukadu Estuary in Chennai, India, transported to the laboratory and maintained in an aerated system with continuous water circulation–biofiltration. WSSV-free P. monodon were challenged by feeding them only once with WSSV-infected tissues of P. monodon. Cumulative mortality (100%) of the infected individuals was determined. Tissues from infected and uninfected shrimp such as muscles, hepatopancreas, heart, gills and eye tissues (100 mg of each) and haemolymph (50 μl) were subjected to SDS-PAGE. In infected muscle tissue, six newly expressed proteins were detected. In infected haemolymph, four new proteins and three intensely expressed high molecular weight proteins were observed. Three intensely expressed high molecular weight proteins were detected in infected heart tissue and two new proteins in infected hepatopancreatic tissues. In infected gill tissues, two new protein bands and three intensely expressed high molecular weight proteins were detected on comparison with uninfected tissues. Similarly, two intensely expressed protein bands were seen in the infected as compared with the uninfected eye tissues. The protein profiles of the muscle tissue from 50 different naturally infected (WSSV) shrimp were analyzed. Eleven different new protein bands appeared in the infected muscle tissues when compared to the control muscle tissues whereas; in muscle tissue six new proteins were observed both in naturally and experimentally WSSV infected shrimp. The current study has shown that the protein expression patterns of the infected tissues of P. monodon have been drastically altered by WSSV infection. Western blot analysis revealed that one of the newly expressed 53 kDa protein in the infected muscle represents the WSSV envelope protein.

Proteomic analysis of proteins that binds specifically to the homologous repeat regions of white spot syndrome virus.

White spot syndrome virus (WSSV) is a major pathogen in the cultivated shrimp. Nine homologous repeat regions (hrrs) have been reported interspersed throughout the WSSV genome. In this investigation, the protein fraction that specifically bound to the hrrs was isolated by using DNA-affinity chromatography. A total of 9 (S1 to S9) and 5 (C1 to C5) proteins separated from the WSSV infected shrimp and the healthy shrimp, respectively, were detected by using two-dimensional polyacrylamide gel electrophoresis, and 6 proteins changed with WSSV infection were analyzed by mass spectrometry (MS). One (S4) of the 6 proteins examined was identified as WSSV ORF59 protein, and another (S3) was a shrimp arginine kinase. No homologous proteins were found with the remaining 4 proteins by searching in the WSSV ORF database and NCBI database. The specific binding site of the 6 proteins was then determined by gel mobility shift assay (GMSA). Temporal analysis revealed that ORF59 gene was transcribed at the early stage of the infection. The results we obtained provide important information to understand WSSV replication. The combination of DNA-affinity chromatography, 2D-PAGE and MS approaches should have general application to the identification of gene regulating proteins of WSSV. The results represent the first isolation of a set of proteins that bind to the hrrs, and, furthermore, lead us a new research direction for the prevention and the therapy of WSSV.

Biochemical, physiological and hematological changes in white spot syndrome virus-infected shrimp, Penaeus indicus

The biochemical and hematological changes provoked by white spot syndrome virus (WSSV) in hemolymph, hepatopancreas and muscle of Penaeus indicus were examined. Total carbohydrate, glucose, total protein, amino acids, fatty acids and hemocyanin were measured in healthy and WSSV-infected shrimp. There was a significant increase in glucose and total carbohydrate levels in the hemolymph of WSSV-infected shrimp in comparison to values for healthy shrimp and reductions in muscle and hepatopancreas of infected shrimp. The average total protein and free amino acids were significantly different between two groups in hemolymph, muscle and hepatopancreas. The fatty acid level increased significantly in the hepatopancreas of WSSV-infected shrimp, but was reduced in the hemolymph and muscle of WSSV-infected shrimp in comparison to healthy shrimp. Significant reductions in total hemocyte counts (THC) and hemocyanin contents were observed in WSSV-infected shrimp; hemolymph from WSSV-infected shrimp failed to clot. Some physiological responses such as oxygen consumption and ammonia excretion were examined in both healthy and WSSV-infected shrimp and the results showed reductions in oxygen consumption and ammonia excretion in WSSV-infected shrimp.

A Profound Effect of Hyperthermia on Survival of Litopenaeus vannamei Juveniles Infected with White Spot Syndrome Virus

AbstractThis study was conducted to examine the effect of increasing seawater temperature on White Spot Syndrome Virus (WSSV) infection in juvenile Pacific White shrimp (Litopenaeus vannamei). Infection by WSSV was achieved using two methods, intramuscular injection and per os (oral) administration. Forty injected and 20 per os infected animals were kept in heated tanks at 32.3 ± 0.8 C, and the same number of WSSV infected animals were maintained in tanks at ambient temperature (25.8 ± 0.7 C). Despite the route of exposure, there were no survivors among the animals kept at ambient temperature; whereas, in heated tanks the survival of the WSSV infected juvenile shrimp was always above 80%, suggesting the existence of a beneficial effect from hyperthermia that mitigated the progression of WSSV disease. Moreover, this beneficial effect was not attributable to viral inactivation. Infected animals kept at 32 C had histologically detectable lymphoid organ spheroids suggestive of a chronic viral infection but were PCR negative (hemolymph) for WSSV. These findings might be related to low viral replication in WSSV‐infected shrimp held at the higher environmental temperature. When the WSSV‐infected shrimp were transferred from 32 C to ambient temperature, the mortality from WSSV ensued and was always 100%. Although the mechanism related to the beneficial effect of heating was not determined, our results indicate that increasing the water temperature modifies dramatically the natural history of the WSSV disease and the survival curves of WSSV‐infected juvenile Pacific White shrimp.