White Spot Syndrome Virus Outbreak Research Articles

Comparative genomics highlights the virulence and evolutionary trajectory of white spot syndrome virus.

White spot syndrome virus (WSSV) poses a significant threat to shrimp aquaculture, leading to substantial economic losses. This study aims to evaluate the virulence and evolution of recent WSSV outbreaks in Japan. Shrimp infected with WSSV were collected from Okinawa, Miyakojima and Miyazaki prefectures, yielding a total of seven isolates. Through injection and immersion tests, the lethal dose 50% endpoints were determined. Genomic analysis revealed isolates with sizes ranging from 288 to 299 kbp, sharing ~99% nucleotide identity with the reference genome (CN01: NC_003225.3). Variant analysis identified 1197 forms, primarily single-nucleotide polymorphisms, with Miyakojima isolates displaying the highest diversity. Frameshift mutations, notably in ORFs such as wsv006, wsv011, wsv091 and wsv403, were observed across all isolates. Phylogenetic analysis indicated clustering of Miyakojima isolates, suggesting similar outbreak intensities. Furthermore, isolates exhibited smaller genomic sizes compared with the reference genome, indicating ongoing WSSV evolution. Notably, a high frameshift mutation in wsv403, a viral E3 ubiquitin ligase, implies its potential role in the observed outbreaks, particularly in Miyakojima. This study addresses the research question regarding the virulence and evolutionary dynamics of WSSV outbreaks, proposing a hypothesis that genetic variations contribute to the severity and spread of WSSV in shrimp aquaculture.

Modulation of the unfolded protein response by white spot syndrome virus via wsv406 targeting BiP to facilitate viral replication

Outbreaks of diseases are often linked to environmental stress, which can lead to endoplasmic reticulum (ER) stress and subsequently trigger the unfolded protein response (UPR). The replication of the white spot syndrome virus (WSSV), the most serious pathogen in shrimp aquaculture, has been shown to rely on the UPR signaling pathway, although the detailed mechanisms remain poorly understood. In this study, we discovered that WSSV enhances its replication by hijacking the UPR pathway via the viral protein wsv406. Our analysis revealed a significant upregulation of wsv406 in the hemocytes and gills of infected shrimp. Mass spectrometry analysis identified that wsv406 interacts specifically with the immunoglobulin heavy-chain-binding protein (BiP) in shrimp Litopenaeus vannamei. Further examination revealed that wsv406 binds to multiple domains of LvBiP, inhibiting its ATPase activity without disrupting its binding to UPR stress receptors. Silencing either wsv406 or LvBiP resulted in a reduction in WSSV replication and improved shrimp survival rates. Further, wsv406 activation of the PRKR-like ER kinase (PERK)-eukaryotic translation initiation factor 2α (eIF2α) and activating transcription factor 6 (ATF6) pathways was demonstrated by a decrease in the phosphorylation of eIF2α and the nuclear translocation of ATF6 when wsv406 was silenced during WSSV infection. This activation facilitated the transcription of WSSV genes, promoting viral replication. In summary, these findings reveal that wsv406 manipulates the host UPR by targeting LvBiP, thereby enhancing WSSV replication through the PERK-eIF2α and ATF6 pathways. These insights into the interaction between WSSV and host cellular machinery offer potential targets for developing therapeutic interventions to control WSSV outbreaks in shrimp aquaculture.

Estimating the basic reproduction number and final epidemic size of white spot syndrome virus outbreak in Penaeus japonicus in aquaculture ponds

White spot syndrome virus (WSSV) triggers white spot disease and high mortality in farmed shrimp. To control the WSSV epidemic, understanding its dynamics through epidemiological analysis is essential. However, measuring the mortality by WSSV infection is difficult due to the rapid increase in mortality and the availability of epidemiological data on WSSV epidemics in aquaculture ponds is limited. In this study, we conducted an epidemiological analysis using field data collected during the early phase of the outbreak to estimate the complete picture of the outbreak. Thereafter, we constructed a mathematical model describing the WSSV epidemic in aquaculture ponds and fitted our model with data on WSSV outbreaks among kuruma shrimp (Penaeus japonicus) farmed in 40,000 m2 aquaculture ponds in Japan. We estimated the basic reproduction number (R0), which measures the average number of secondary infections by a single infected individual, i.e. the transmissibility of a pathogen. The estimated R0 per pond was large (3.21–4.56), suggesting that with no intervention WSSV outbreaks will likely result in large final epidemic size, with 98.0–99.7% of entire population infected by the virus. Once WSSV infection is detected in a pond, urgent intervention, such as enhanced removal of dead shrimp and harvesting all farmed shrimps immediately, is required.

Evaluation of the antiviral activity of chlorogenic acid against white spot syndrome virus

The rapid development of crustacean aquaculture is threatened by white spot syndrome virus (WSSV), which is one of the deadliest pathogens affecting various crustacean species. Based on antiviral plant screening, we found that chlorogenic acid (CGA), a polyphenolic component of Arctium lappa Linn., possessed strong activity against WSSV infection in a red swamp crayfish (Procambarus clarkii) model. The results revealed that CGA dose-dependently inhibited WSSV proliferation in the gill and haemocytes with the inhibition rates (50 mg/kg) were 94.7% and 95.03%, respectively. Through a serial of mechanical experiments, we found that CGA arrested WSSV replication by regulating innate immune defense to reduce viral gene transcription, inducing apoptosis to restrict viral spread, and enhancing anti-inflammatory and antioxidant activities to alleviate oxidative and inflammatory damage caused by WSSV. Significant improvements in survival of WSSV infected crayfish have been made through injection and dietary administration of CGA compared to control group. In a static cohabitation model, pre-incubation of CGA suppressed the horizontal transmission of WSSV between infected donor crayfish and health crayfish. Thus, we have identified CGA as a potent WSSV inhibitor with high potential for further development as prophylaxis and therapy agents against WSSV outbreak in crustacean aquaculture.

Cinnamaldehyde, a major component of Cinnamomum cassia Presl ethanol extract, has the potential to unlock the outbreak of WSSV

The white spot syndrome virus (WSSV) is rapid onset and high mortality, which has caused a devastating blow to shrimp culture around the world. However, there are no effective measures to prevent and control the WSSV. Thus, it is urgent to find a safe and efficient measures to prevent the outbreak of WSSV. Here, the anti-WSSV activities of 20 Chinese herbal medicine ethanol extracts were evaluated in Litopenaeus vannamei. Among these, the ethanol extract of cinnamon (Cinnamomum cassia Presl) had the highest inhibition rate of 91% on WSSV genome replication. Surprisingly, cinnamaldehyde, the main component of cinnamon extract, has a simple structure and could reduce the copy level of viral genome in shrimp, with the strongest inhibitory effect of 93% at 72 h, and more than 40% of diseased shrimp survived. Further experiments showed that cinnamon extracts and cinnamaldehyde could prolong the cumulative survival time of WSSV-infected larvae, and continuous treatment with cinnamaldehyde could maintain the replication of WSSV genome at a low level. In addition, cinnamon extracts and cinnamaldehyde could significantly inhibit the horizontal transmission of virions at 72 h by 71% and 42%, respectively. Obviously, this further reduces the risk of WSSV outbreak. Similarly, cinnamaldehyde pre-incubated shrimp and virions could improve the tolerance of shrimp to WSSV and reduce the infectivity of virions. Taken together, cinnamon extract and cinnamaldehyde could inhibit WSSV genome replication and reduce mortality rate of WSSV-infected shrimp. The results provided a scientific basis for the use of cinnamon extract and cinnamaldehyde to unlock the outbreak of WSSV, and were worthy of further study and consideration.

Taxifolin Inhibits WSSV Infection and Transmission by Increasing the Innate Immune Response in Litopenaeus vannamei.

An outbreak of white spot syndrome virus (WSSV) can hit shrimp culture with a devastating blow, and there are no suitable measures to prevent infection with the virus. In this study, the activity of active molecules from Chinese herbs against WSSV was evaluated and screened. Taxifolin had the highest rate (84%) of inhibition of the WSSV infection. The viral infectivity and genome copy number were reduced by 41% when WSSV virion was pretreated with taxifolin prior to shrimp infection. A continuous exchange of taxifolin significantly reduced the mortality of shrimp infected with WSSV. Due to the WSSV virion infectivity being affected by taxifolin, the horizontal transmission of the virus was blocked with an inhibition rate of up to 30%, which would further reduce the cost of a viral outbreak. Additionally, the viral genome copy number was also reduced by up to 63% in shrimp preincubated in taxifolin for 8 h. There may be a connection to the enhancement of innate immunity in shrimp that resulted in a 15% reduction in mortality for taxifolin-fed shrimp after the WSSV challenge. After dietary supplementation with taxifolin, the resistance of larvae to WSSV was improved, indicating that taxifolin may be a potential immunostimulant for shrimp to prevent WSD. Therefore, the results indicate that taxifolin has application potential for blocking a WSSV outbreak and reducing the loss of shrimp culture.

Transcriptome analysis of Marsupenaeus japonicus hepatopancreas during WSSV persistent infection

White Spot Syndrome Virus (WSSV) can cause a large-scale death of cultured shrimp and significant damage to the shrimp farming industry. Marsupenaeus japonicus is one of the world’s most important economically farmed shrimp. This study found that some M. japonicus survived the spontaneous outbreak of WSSV. Surprisingly, these virus-carrying shrimp showed no apparent illnesses or outbreaks of white spot disease in the subsequent cultivation, and their body size was substantially smaller than healthy shrimp, indicating a long-term fight between the host and the virus. To investigate this interesting phenomenon, we analyzed the transcriptomes of healthy shrimp and survived shrimp through the RNA-Seq platform, attempting to reveal the underlying molecular mechanism of the struggle between M. japonicus and WSSV. Transcriptional analysis showed that a total of 37,815 unigenes were assembled, with an average length of 1,193.34 bp and N50 of 2,049 bp. In the KEGG pathway, enrichment analysis of DEGs pathways related to immunity, biosynthesis, and growth metabolism was enriched, including pentose phosphate pathway, glycerophospholipid metabolism, fatty acid biosynthesis, Wnt signaling pathway, biosynthesis of amino acids, ascorbate, and aldarate metabolism. Our data showed a delicate balance between M. japonicus and WSSV infection: On the one hand, WSSV infection can cause host metabolism and biosynthesis disorders in the host, and the virus consumes a portion of the material and energy required for shrimp average growth and reproduction. If WSSV infection persisted for a long time, then the growth rate of M. japonicus decreased. On the other hand, the host can regulate immune defense to resist subsequent viral infection. This study reveals the underlying molecular mechanism of a long-term battle of M. japonicus against WSSV infection, providing novel insights for preventing WSSV persistent infection in M. japonicus and other farmed shrimp species.

Herbicide atrazine exposure induce oxidative stress, immune dysfunction and WSSV proliferation in red swamp crayfish Procambarus clarkii

Atrazine is considered as a potential environmental endocrine disruptors and exhibits various toxic effects on animals. It has a great impact in the aquatic ecosystems, but there are few studies on its immunotoxicity in crustaceans. In the present study, the Procambarus clarkii were utilized to assess the immune toxicity after 0.5 mg/L and 5 mg/L atrazine exposure. A significant decrease in total hemocytes count (THC) was observed at 5 mg/L atrazine exposure throughout the experiment. The activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) were significantly inhibited, but the content of reactive oxygen species (ROS) and malondialdehyde (MDA) were up-regulated, indicating the potential oxidative stress. The analysis of the integrated biomarker response (IBR) showed the induction of oxidative stress biomarkers and the inhibition of antioxidants. After 5 mg/L atrazine exposure for 144 h, the integrity of crayfish hepatopancreas was destroyed with disappeared connections between tubules and increased liver tubules vacuoles. The relative expression levels of different immune genes in hepatopancreas after atrazine exposure were measured. Most of these genes were suppressed and exhibited a certain dose-dependent effect. The results of crayfish white spot syndrome virus (WSSV) replication shown the amount of virus in muscle was significantly higher and exhibited a higher mortality rate at 5 mg/L group than other groups. The present study determined the impact of atrazine exposure on WSSV outbreaks, and also provide an important basis for further assessing the occurrence of pesticides on diseases of P. clarkii.

Diagnostic Molecular Investigation of White Spot Syndrome Virus Finds No Infection in Wild White Shrimp and Brown Shrimp along the Texas Gulf Coast.

White spot syndrome virus (WSSV) is a virulent disease that disrupts shrimp farm operations throughout the world. While the United States has had only limited outbreaks of WSSV within the past several decades, it is important to ensure that this disease does not infect wild penaeid shrimp populations. In Texas, there is a potential for WSSV to spread to wild penaeid populations in the Gulf of Mexico via infected imported nonnative bait shrimp, imported broodstock, or wild crustacean hosts. Due to these potential threats, the Texas Parks and Wildlife Coastal Fisheries Division monitored WSSV in wild brown shrimp Farfantepenaeus aztecus and white shrimp Litopenaeus setiferus from seven major bay systems along the Texas coast during 2019. While no positive samples were detected from the collected shrimp, a power analysis illustrated a potential for low-level WSSV prevalence within Texas shrimp populations that would not be detectable by this monitoring survey. Overall, WSSV does not appear to be a major threat in the Texas region of the Gulf of Mexico, but continual observation and monitoring of wild penaeid shrimp is necessary to protect this resource from future WSSV outbreaks.

Variation in biotic and abiotic factors associated with white spot syndrome virus (WSSV) outbreak in shrimp culture ponds

Shrimp production in India has gradually increased since 2009 with the introduction of Penaeus vannamei. Most coastal states in India have been important contributors to P. vannamei production. However, among the many challenges faced in sustainable shrimp farming, prevention of viral diseases and pond water quality management remain major concerns. In this study, 27 shrimp ponds located in Kalpakkam and Elavur regions of Tamil Nadu were monitored to characterise the pond water parameters including pH, salinity, temperature, alkalinity, ammonia, nitrite, hardness, dissolved oxygen (DO) and Vibrio spp. load. Sudden outbreaks of white spot syndrome virus (WSSV) were observed in some ponds which were found to be associated with variations in abiotic parameters. Parameters such as pH, DO and nitrite were observed to be within the permissible range, while temperature, salinity, Vibrio spp. load and ammonia were relatively higher in certain ponds. The influence of these abiotic factors triggering WSSV outbreak were investigated in this study.

Protection of Caridea Against White Spot Syndrome Virus

White spot syndrome virus (WSSV) belongs to a new virus family, Nimaviridae, genus Whispovirus and contains a large circular double-stranded DNA genome of 292,967 bp. WSSV virions are ellipsoid to bacilliform, enveloped particles with a distinctive tail-like appendage at one end. They can be found throughout the body of infected shrimp. The virions contain one nucleocapsid with a typical striated appearance and 5 major and at least 13 minor proteins. WSSV, which was first discovered in Southeast Asia around 1992, is currently the most serious viral pathogen of shrimp worldwide. It causes up to 100% mortality within 7 to 10 days in commercial shrimp farms, resulting in large economic losses amounting to billions of US dollars across different countries to the shrimp farming industry. In a natural situation, shrimp become infected through both oral and water-borne routes, and the gills are thought to be a major point of viral entry. Considering the global economic and sociological importance of shrimp farming and its continued high growth, the development of novel control measures becomes necessary against the outbreak of WSSV. A number of strategies have been used to control WSSV, each with some limitations. Conventional control strategies such as improvement of environmental conditions, stocking of pathogen-free post-larvae, and augmentation of disease resistance by oral immune-stimulants or probiotics are currently employed to control WSSV infection. Use of recombinant viral proteins as vaccines that induce a specific immune response and protection has been demonstrated to control WSSV. Other studies have shown successful vaccination of shrimp with DNA vaccines that have prolonged effects. The RNA interference (RNAi) mediated silencing of targeted viral mRNAs holds tremendous potential for controlling shrimp diseases. The silencing of viruses using RNAi has been experimentally demonstrated for WSSV in shrimp by injecting or feeding synthetic siRNA, long double-stranded RNA (dsRNA), and short/long-hairpin RNA (shRNA/lhRNA) prepared by in vitro transcription or expressed in bacteria. In addition to targeting viral proteins, protection of WSSV has also been achieved by dsRNA targeted against shrimp PmRab7, a protein important for viral entry into the host cells. Antisense constructs offered strong protection in WSSV challenged shrimp, P. monodon, with a corresponding decrease in viral load. Antisense constructs expressing VP24 and VP28 offered the best protection with a consistent reduction in WSSV copy number in both cell culture and in experimental shrimp. The advantage of using antisense constructs is their lack of toxicity and immunogenicity and their high specificity towards the desired target. The usage of edible pellet feed coated with dsRNA against WSSV has shown promising results. Overall, the present investigation clearly demonstrates that it is possible to induce strong protection in shrimp against WSSV infection using host promoter-driven antisense constructs in controlled laboratory-scale experiments. However, it is important to develop a simple and efficient delivery system for extending this study to the field level.

Impact of combinations of brown seaweeds on shrimp gut microbiota and response to thermal shock and white spot disease

Dietary supplementation with seaweeds has the potential to improve the immune response and physiological performance of marine shrimp under stressful conditions. This work evaluated the effect of dietary supplementation using different ratios of the brown seaweeds Sargassum filipendula (S) and Undaria pinnatifida (U) on the gut microbiota as well as on the resistance to thermal shock and White Spot Syndrome Virus (WSSV) of Litopenaeus vannamei. Additionally, hemocyte lipid and protein profiles were determined by mass spectrometry (MALDI-TOF MS), before and after each stress condition. Shrimp were fed diet containing different seaweed combinations (S%:U% ratios included 0.5S:1U, 0.5S:2U and 0.5S:4U) for 15 days before the metagenomic and thermal shock assessments, and for 21 days before the viral challenge. Following the feeding trial, shrimp were subjected to thermal shock (28.6 °C to 11.5 °C for 1 h, and then back to 28 °C) or were experimentally infected with WSSV. Cumulative mortality was monitored during 24 and 96 h after thermal shock and WSSV challenge, respectively. Hemocyte sampling for MALDI-TOF MS was performed before and 15 min after thermal shock, as well as before and 24 h after viral infection. The dietary supplementation with combinations of brown seaweeds conferred protection against WSSV, but not against the thermal shock. Mortality rates of animals fed 0.5S:2U and 0.5S:4U diets were substantially lower (28.1 and 31.3%, respectively) than the control untreated group (78.1%) at 96 h after WSSV challenge. Thermal shock caused pronounced changes in hemocyte lipid and protein profiles, regardless of the diet, particularly affecting molecules involved in membrane fluidity, lipid and energy metabolism, immune response, apoptosis and antioxidant capacity. Hemocyte molecular content of WSSV-infected animals was different from that of the control group, showing shifts in particular lipid and protein groups that could be potentially associated with the early induction of apoptosis as well as the modulation of lipid metabolism and antimicrobial compounds. Metagenomic analysis revealed that the increasing levels of U. pinnatifida in the diet reduced shrimp gut microbial richness, while enhanced microbial diversity, especially in 0.5S:1U and 0.5S:2U treatments. Such response was mainly related to changes in the relative abundances of the families Rhodobacteraceae, Flavobacteriaceae and Cellulomadaceae. In conclusion, our findings indicate that feeding shrimp diets containing a mixture of both seaweeds affect their gut microbiota and could potentially reduce mortality rates during WSSV outbreaks, triggering intracellular and physiological mechanisms that could also ameliorate the deleterious impacts of other environmental stressors.

Gardenia jasminoides Ellis inhibit white spot syndrome virus replication in red swamp crayfish Procambarus clarkii

As one of the most dangerous pathogens in the aquaculture of crustaceans, white spot syndrome virus (WSSV) induces a high mortality rate and huge economic losses in crustacean industries. Up to now, there are no commercially available drugs to control the virus. Thus, it is important to find an antiviral drug to combat highly lethal WSSV outbreaks. In the present study, the anti-WSSV activities of 23 medicinal plant extracts were investigated in crayfish Procambarus clarkii. In order to better evaluate the antiviral activities of plant extracts, it was important to build a WSSV infection model in crayfish first. The results of WSSV infection showed that WSSV could infect most tissues of crayfish, and the heaviest infected tissue is the gills. The time course curve of WSSV amount change in crayfish assumed a very similar shape with the typical viral one-step growth curve. On the basis of virus infection model, the anti-WSSV activities of 23 plant extracts were investigated. Among these plants, Gardenia jasminoides showed the highest inhibition on WSSV replication, with 92.31%. A further study showed that G. jasminoides improved survival rate of WSSV-challenged crayfish. Mechanistically, G. jasminoides reduced Hsp70 expression and virus immediate-early gene ie1, early gene DNApol, late gene VP28 transcript, indicating that G. jasminoides inhibited WSSV replication via blocking the immediate-early stage gene ie1 transcript. Furthermore, the expression of antioxidants (cMnSOD, mMnSOD, CAT and GST) and apoptosis-related factors (Bax and Bax-inhibitor-1) were significantly increased in G. jasminoides-treated crayfish, suggesting that G. jasminoides could modulate apoptosis-related factors and possessed anti-oxidative activity in crayfish. Taken together, G. jasminoides could inhibit WSSV replication and improve survival rate of WSSV-challenged crayfish. This outcome offers a scientific basis for the use of extracts of G. jasminoides against WSSV, and it is worth focusing on the isolation and identification of effective active compounds from G. jasminoides.

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.

Circulatory white spot syndrome virus in South-West region of Bangladesh from 2014 to 2017: molecular characterization and genetic variation

White Spot Syndrome Virus (WSSV), the etiological agent of White Spot Disease (WSD) is a major impediment for shrimp aquaculture in the worldwide. A critical threshold level of WSSV load in infected shrimp is an important trait for disease manifestation and WSSV transmission in cultured shrimp and subsequently make outbreaks. The present study investigated 120 naturally infected cultured shrimp samples by SYBR Green based qPCR assay for WSD diagnosis and quantification of WSSV load. Among them, 94 samples resulted a variable count of WSSV load ranging from 2.1 × 108 to 2.64 × 1014 copies/g of shrimp tissue. The severity of WSSV infection was assessed based on the established critical threshold load of WSSV in shrimp tissue. Compared to the established critical threshold value of WSSV load in shrimp tissue, our findings showed the horrifying scenario of the severity of WSSV infection in cultured shrimps of Bangladesh that was found to be above the critical limit to initiate an outbreak in the Bangladeshi shrimp aquaculture industry. The latest phylogenetic pattern was altered from the former monophyletic history among WSSVs of Bangladesh due to a variation at 500th nucleotide of VP28 coding gene. Viruses characterized from recent outbreaks in 2015 and 2017 displayed amino acid substitution at position 167 (G→E) on the surface of VP28 protein which has demonstrated the probable replacement of indigenous virus pool. Therefore, it is imperative to take initiative for the management and prevention of WSSV outbreak to sustain shrimp aquaculture in South-West region of Bangladesh.

Risk factors associated with white spot syndrome virus outbreaks in marine shrimp farms in Rayong Province, Thailand.

The purpose of this study was to determine risk factors for white spot disease (WSD) in Rayong, Thailand. A study was conducted from October 2014 to March 2015 to identify potential farm-level risk factors using a validated questionnaire. We completed 1 questionnaire for each farm; a total of 38 questionnaires from the case farms and 127 questionnaires from the control farms were collected. The results showed that the presence of WSD in previous crops and the use of seawater were risk factors (p < 0.01), indicating that the environment plays an important role in WSD outbreaks in Rayong. Good management practices for pond preparation and other mitigation steps should be part of a control measure program for WSD in this region.

Analysis of repeated compound units in ORF94 of white spot syndrome virus isolated from Litopenaeus vannamei from outbreak and non outbreak shrimp farms in Sonora, Mexico

White spot syndrome virus (WSSV) is the viral pathogen with the most negatively impact on shrimp farming. In Sonora, Litopenaeus vannamei culture has decreased 50% during 2010-2012 due to WSSV outbreaks. The ORF94 has proven to be most useful for analysis of WSSV variability, several studies have suggested a correlation between its Repeat Units (RUs) and WSSV virulence as follows: the fewer RUs (

Temporal and spatial dynamics of white spot syndrome virus in the Chinese mitten crab, Eriocheir sinensis

White spot syndrome virus (WSSV) is the most severe viral pathogen to the crustacean aquaculture industry worldwide. Recently, serious WSSV outbreaks caused catastrophic losses in the Chinese mitten crab, Eriocheir sinensis in Jiangsu Province, Eastern China. However, to date, little is known about its infection mechanism in the new natural host. This study aimed to reveal the temporal and spatial dynamics of WSSV in E. sinensis. The slow viral growth in the early stage of infection was the light infection stage (from 0 to 24 hpi), and the exponential growth stage that followed was the logarithmic phase (from 24 to 72 hpi). The viral growth curve ended with the plateau phase (from 72 to 144 hpi) which demonstrated a consistent high level of viral load and accompanied heavy crab mortality. The viral load increased as time progressed with similar growth curves, however, at different degrees. The viral copy numbers of tissues at different time intervals, analysed using one-way analysis of variance (anova), showed significant differences between tissues at all time points (P < 0.05). Infection was detectable as early as 6 hpi in all the tissues screened. The severity of infection was found to be maximum in gill and pleopods, which could be recommended for diagnostic testing. This study might provide important data to analyse theoretically the interaction between WSSV and the host.

Effect of ingestion and waterborne routes under different shrimp densities on white spot syndrome virus susceptibility in three commercially important penaeid shrimps

A study was undertaken to evaluate some factors that are important for better management of the white spot syndrome virus (WSSV). We examined the likelihood of that the mud crab (Scylla serrata) is a potential carrier of WSSV in shrimp farms and then compared susceptibility of three shrimp species to WSSV, and finally tested the effects of shrimp stocking density and transmission routes on the intensity of WSSV infection under experimental conditions. Mud crabs were collected from the crab fattening unit of Pichavaram mangroves area, southeast coast of India. The infectivity test was conducted on Penaeus monodon, P. indicus, Litopenaeus vannamei under three different shrimp densities and two different routes of infection. Each treatment was executed in triplicate of 100L tanks. The results showed that S. serrata is a carrier of WSSV. Among three species of shrimps, P. indicus was most susceptible and L. vannamei was most resistant in term of cumulative mortality. Ingestion route was more effective than waterborne route on WSSV outbreaks. Cumulative mortality of shrimps due to WSSV infection increased with increasing shrimp density. The result of this study is important to improve management especially to minimize the WSSV infection in the shrimp farms.

DETECTION AND ANALYSIS OF EARLY GENES OF WHITE SPOT SYNDROME VIRUS IN PENAEID SHRIMP

White spot syndrome virus (WSSV) is the most lethal pathogenic virus affecting the penaeid shrimp. Outbreak of WSSV causes high mortality among the populations of cultured penaeid shrimp. Aim of the present study was to diagnose the WSSV in early stage of infection. Immediate early genes are genes that are activated due to presence of cellular stimuli and have significant role in replication and proliferation of virus. In this study, wsv303 and wsv477 genes were chosen for analysis. This study demonstrates the detection of WSSV using primers designed from early genes and sequences the Indian isolates for homology analysis. Polymerase chain reaction was performed for the detection confirmation and the PCR products were cloned. Different organs such as gill, head soft tissue, heart tissue, intestine and tail tissue had been used for the PCR assay. Both genes were amplified at the size of 420 bp and 457 bp, respectively. Different duration samples of WSSV post-infection muscle DNAs were analyzed with the two primers and compared with OIE-nested PCR method convincing the early detecting ability of the virus. Sequencing analysis was performed with other isolates from France, China, The Netherlands and Taiwan. Phylogenetic analysis revealed that the Indian isolate was closely related to other isolates.