Spatial and temporal patterns of white spot disease in Rayong Province, Thailand, from october 2015 to september 2018.

This study aimed to analyze the spatial and temporal patterns of white spot disease (WSD) in shrimp farms in Rayong Province, Thailand, between October 2015 and September 2018. The longitudinal data of all active shrimp farms were collected and categorized into two groups: cases and non-cases. A space-time permutation scan, epidemic curve, and time-series analysis were used to evaluate the spatiotemporal patterns. We assessed a total of 1126 ponds across 176 farms in two districts (Klaeng and Mueang Rayong) and identified three significant (P < 0.05) clusters of WSD cases. The biggest cluster encompassed 21 geographical coordinates. This cluster had a radius of 1.14 km and occurred between January 31, 2017, and February 28, 2017. The epidemic curve showed that the biggest outbreak peaked from December 2017 to February 2018. In the time-series analysis, the highest probability of actual WSD cases was at the beginning of each calendar year, consistent with the prominent high probability recorded in WSD forecasts. Our analysis presents the interaction between hotspot areas and time period. These results should help the relevant authorities implement appropriate surveillance programs and control measures to limit the occurrence and transmission of WSD.

Incidence of hepatitis A and hepatitis E viruses and norovirus and rotavirus in fish and shrimp samples caught from the Persian Gulf / [Incidência de vírus da hepatite A e hepatite E e norovírus e rotavírus em amostras de peixes e camarões capturados no Golfo Pérsico]

Foodborne viruses including hepatitis A virus (HAV), norovirus (NoV), rotavirus (RoV) and hepatitis E virus (HEV) are easily transmitted through contaminated seafoods. The current research was done to assess the incidence of RoV, NoV GI and GII,hAV and hEV in fish and shrimp samples caught from the Persian Gulf, Iran. Three-hundred and twenty fish and shrimp samples were collected. The presence of foodborne viruses were assessed by the real-time PCR. Forty-nine out of 320 (15.31%) fish and shrimp samples were positive for foodborne viruses. Distribution of hAV, NoV GI and NoV GII amongst all studied samples were 0.93%, 5.93% and 8.43%, respectively. hEV and RoV viruses were not found in studied samples. Parastromateus niger and Scomberomorus commerson fish and Penaeus monodon shrimp were the most frequently contaminated samples. Simultaneous incidence of hAV and NoV GI and hAV and NoV GII were 0.31% and 0.93%, respectively. Distribution of foodborne viruses in samples collected through spring, summer, autumn and winter seasons were 14.28%, 9.33%, 11.76% and 24.44%, respectively. Findings revealed that the incidence of foodborne viruses was significantly associated with seafood species and also season of sampling.(AU)

Vírus transmitidos por alimentos, incluindo hepatite A (HAV), norovírus (NoV), rotavírus (RoV) e hepatite E (HEV) são facilmente transmitidos através de frutos do mar contaminados. Esta pesquisa foi realizada para avaliar a incidência de RoV, NoV GI e GII, hAV e hEV em amostras de peixes e camarões capturadas no Golfo Pérsico, Irã. Foram coletadas 300 amostras de peixes e camarões. A presença de vírus transmitidos por alimentos foi avaliada por PCR em tempo real. Quarenta e nove das 320 amostras de peixes e camarões (15,31%) foram positivas para vírus transmitidos por alimentos. A distribuição de hAV, NoV GI e NoV GII entre as amostras estudadas foi 0,93%, 5,93% e 8,43%, respectivamente. Os vírus hEV e RoV não foram encontrados nas amostras estudadas. Os peixes Parastromateus niger e Scomberomorus commerson e o camarão Penaeus monodon foram as amostras mais frequentemente contaminadas. A incidência simultânea de hAV e NoV GI, e hAV e NoV GII foi de 0,31% e 0,93%, respectivamente. A distribuição dos vírus transmitidos por alimentos nas amostras coletadas na primavera, verão, outono e inverno foi de 14,28%, 9,33%, 11,76% e 24,44%, respectivamente. Os resultados demonstram que a incidência de vírus transmitidos por alimentos foi significativamente associada às espécies de frutos do mar e também à época da amostragem.(AU)

Detection and Phylogenetic Analyses of Taura Syndrome Virus from Archived Davidson's-Fixed Paraffin-Embedded Shrimp Tissue.

Taura syndrome is a World Organization for Animal Health (OIE)-listed disease of marine shrimp that is caused by Taura syndrome virus (TSV), a single-stranded RNA virus. Here we demonstrate the utility of using 15-year-old archived Davidson's-fixed paraffin-embedded (DFPE) shrimp tissues for TSV detection and phylogenetic analyses. Total RNA was isolated from known TSV-infected DFPE tissues using three commercially available kits and the purity and ability to detect TSV in the isolated RNA were compared. TSV was successfully detected through RT-qPCR in all the tested samples. Among the TSV-specific primers screened through RT-PCR, primer pair TSV-20 for the RNA-dependent RNA polymerase (RdRp), primers TSV-15 and TSV-16 for the capsid protein gene VP2 and primers TSV-5 for the capsid protein gene VP1 amplified the highest number of samples. To assess the phylogenetic relation among different TSV isolates, the VP1 gene was amplified and sequenced in overlapping segments. Concatenated sequences from smaller fragments were taken for phylogenetic analyses. The results showed that the TSV isolates from this study generally clustered with homologous isolates from the corresponding geographical regions indicating RNA derived from DFPE tissues can be used for pathogen detection and retrospective analyses. The ability to perform genomic characterization from archived tissue will expedite pathogen discovery, development of diagnostic tools and prevent disease spread in shrimp and potentially other aquaculture species worldwide.

Exosome-mediated apoptosis pathway during WSSV infection in crustacean mud crab.

MicroRNAs are regulatory molecules that can be packaged into exosomes to modulate cellular response of recipients. While the role of exosomes during viral infection is beginning to be appreciated, the involvement of exosomal miRNAs in immunoregulation in invertebrates has not been addressed. Here, we observed that exosomes released from WSSV-injected mud crabs could suppress viral replication by inducing apoptosis of hemocytes. Besides, miR-137 and miR-7847 were found to be less packaged in mud crab exosomes during viral infection, with both miR-137 and miR-7847 shown to negatively regulate apoptosis by targeting the apoptosis-inducing factor (AIF). Our data also revealed that AIF translocated to the nucleus to induce DNA fragmentation, and could competitively bind to HSP70 to disintegrate the HSP70-Bax (Bcl-2-associated X protein) complex, thereby activating the mitochondria apoptosis pathway by freeing Bax. The present finding therefore provides a novel mechanism that underlies the crosstalk between exosomal miRNAs and apoptosis pathway in innate immune response in invertebrates.

First detection of white spot syndrome virus (WSSV) in the mud shrimp Austinogebia edulis in Taiwan.

The white spot syndrome virus (WSSV) causes mass mortalities in the aquaculture of shrimps worldwide. The mud shrimp Austinogebia edulis (Ngoc-Ho & Chan, 1992) is an economically important sea food item occurring along the west coast of Taiwan. While the population of A. edulis began to decrease with some fluctuations in the last decade, the current study aims to discover the causes for such sporadic population decline. This study explores the effects of microbial pathogens and innate immunity on the populations of A. edulis. Here, we report firstly about WSSV infection of A. edulis from the coastal zone of western Taiwan which is one of the possible causes of population decrease of A. edulis in Shengang. However, WSSV infection is not the only reason for its population decrease because a similar infection rate of WSSV was found in Wangong. Population changes may be related to both environmental pollution stress and WSSV. Both factors likely caused a massive reduction of hemocytes and an abnormal increase of phenoloxidase and superoxide dismutase activity, which were spectrophotometrically measured. Since there is no effective way to treat WSSV infection, improving the coastal environment appears the most effective way to increase the population size of feral shrimps.

Comparative genome analysis reveals a distinct influence of nucleotide composition on virus-host species-specific interaction of prawn-infecting nodavirus.

Discovery of species-specific interaction between the host and virus has drawn the interest of many researchers to study the evolution of the newly emerged virus. Comparative genome analysis provides insights of the virus functional genome evolution and the underlying mechanisms of virus-host interactions. The analysis of nucleotide composition signified the evolution of nodavirus towards host specialization in a host-specific mutation manner. GC-rich genome of betanodavirus was significantly deficient in UpA and UpU dinucleotides composition, whilst the AU-rich genome of gammanodavirus was deficient in CpG dinucleotide. The capsid of MrNV and PvNV of gammanodavirus retains the highest abundance of adenine and uracil at the second codon position, respectively, which were found to be very distinctive from the other genera. ENC-GC3 plot inferred the influence of natural selection and mutational pressure in shaping the evolution of MrNV RdRp and capsid, respectively. Furthermore, CAI/eCAI analysis predicts a comparable adaptability of MrNV in squid, Sepia officinalis than its natural host, Macrobrachium rosenbergii. Thus, further study is warranted to investigate the capacity of MrNV replication in S. officinalis owing to its high codon adaptation index.

Susceptibility of Exopalaemon carinicauda to the Infection with Shrimp Hemocyte Iridescent Virus (SHIV 20141215), a Strain of Decapod Iridescent Virus 1 (DIV1).

In this study, ridgetail white prawns-Exopalaemon carinicauda-were infected per os (PO) with debris of Penaeus vannamei infected with shrimp hemocyte iridescent virus (SHIV 20141215), a strain of decapod iridescent virus 1 (DIV1), and via intramuscular injection (IM with raw extracts of SHIV 20141215. The infected E. carinicauda showed obvious clinical symptoms, including weakness, empty gut and stomach, pale hepatopancreas, and partial death with mean cumulative mortalities of 42.5% and 70.8% by nonlinear regression, respectively. Results of TaqMan probe-based real-time quantitative PCR showed that the moribund and surviving individuals with clinical signs of infected E. carinicauda were DIV1-positive. Histological examination showed that there were darkly eosinophilic and cytoplasmic inclusions, of which some were surrounded with or contained tiny basophilic staining, and pyknosis in hemocytes in hepatopancreatic sinus, hematopoietic cells, cuticular epithelium, etc. On the slides of in situ DIG-labeling-loop-mediated DNA amplification (ISDL), positive signals were observed in hematopoietic tissue, stomach, cuticular epithelium, and hepatopancreatic sinus of infected prawns from both PO and IM groups. Transmission electron microscopy (TEM) of ultrathin sections showed that icosahedral DIV1 particles existed in hepatopancreatic sinus and gills of the infected E. carinicauda from the PO group. The viral particles were also observed in hepatopancreatic sinus, gills, pereiopods, muscles, and uropods of the infected E. carinicauda from the IM group. The assembled virions, which mostly distributed along the edge of the cytoplasmic virogenic stromata near cellular membrane of infected cells, were enveloped and approximately 150 nm in diameter. The results of molecular tests, histopathological examination, ISDL, and TEM confirmed that E. carinicauda is a susceptible host of DIV1. This study also indicated that E. carinicauda showed some degree of tolerance to the infection with DIV1 per os challenge mimicking natural pathway.

ICTV Virus Taxonomy Profile: Nimaviridae.

The family Nimaviridae includes the single species White spot syndrome virus, isolates of which infect a wide range of aquatic crustaceans and cause substantial economic losses. Virions are ellipsoid to bacilliform with a terminal thread-like extension. The circular dsDNA genome is 280-307 kbp with several homologous repeat regions. More than 80 structural and functional proteins have been characterized from 531 ORFs. White spot syndrome is a highly lethal, contagious disease associated with white spot syndrome virus infection of shrimps. This is a summary of the International Committee on Taxonomy of Viruses (ICTV) Report on the family Nimaviridae, which is available at www.ictv.global/report/nimaviridae.

White spot syndrome virus and the Caribbean spiny lobster, Panulirus argus: Susceptibility and behavioral immunity.

The Caribbean spiny lobster Panulirus argus is susceptible to infection by Panulirus argus Virus 1 (PaV1), the only virus known to naturally infect any lobster species. However, P. argus is able to mitigate PaV1 transmission risk by avoiding infected individuals. P. argus may also be susceptible to another lethal virus, White Spot Syndrome Virus (WSSV). WSSV has not been documented in wild populations of spiny lobsters, but has been experimentally transmitted to six other lobster species from the genus Panulirus. Although WSSV has been detected intermittently in wild populations of shrimp in the Caribbean region, the risk to P. argus has not been evaluated. Potential emergence of the disease could result in fisheries losses and ecological disruption. To assess the risk to P. argus, we tested its susceptibility to WSSV via injection and waterborne transmission. We also tested whether healthy lobsters can detect and avoid conspecifics with qPCR-quantifiable WSSV infections. We found P. argus to be highly susceptible to WSSV via intramuscular injection, with mortality reaching 88% four weeks post inoculation. Panulirus argus was also susceptible to WSSV via waterborne transmission, but WSSV burden was low after four weeks via qPCR. Behavioral assays indicated that P. argus can detect and avoid conspecifics infected with WSSV and the avoidance response was strongest for the most heavily infected individuals - a response comparable to PaV1-infected conspecifics. Panulirus argus is the first spiny lobster found to be susceptible to WSSV in the Americas, but it is possible that a generalized avoidance response by healthy lobsters against infected conspecifics provides a behavioral defense and may reduce WSSV infection potential and prevalence. Preliminary evidence suggests that the infiltration of hemolymph constituents into the urine may be the source of the avoidance behavior and could therefore extend to other directly transmitted pathogens in spiny lobster populations preventing them from becoming common in their population.

Survivability of low pathogenic (H9N2) avian influenza virus in water in the presence of Atyopsis moluccensis (Bamboo shrimp).

Low pathogenic avian influenza virus (LPAIV) exhibits an ecological climax with the aquatic ecosystem. The most widely prevalent subtype of LPAIV is H9N2. Wild aquatic birds being the natural reservoirs and ducks, the "Trojan horses" for Avian Influenza Virus (AIV), can contaminate the natural water bodies inhabited by them. The virus can persist in the contaminated water from days to years depending upon the environmental conditions. Various aquatic species other than ducks can promote the persistence and transmission of AIV; however, studies on the role of aquatic fauna in persistence and transmission of avian influenza virus are scarce. This experiment was designed to evaluate the survivability of H9N2 LPAIV in water with and without Atyopsis moluccensis (bamboo shrimp) for a period of 12 days. The infectivity and amount of virus in water were calculated and were found to be significantly higher in water with A. moluccensis than in water without A. moluccensis. The study also showed that A. moluccensis can accumulate the virus mechanically which can infect chicken eggs up to 11 days. The virus transmission potential of A. moluccensis requires further studies.

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.

Recent progress toward the identification of anti-viral immune mechanisms in decapod crustaceans.

The sustainable intensification of crustacean aquaculture, which is dominated by the farming of penaeid shrimp species, continues to be beset by viral disease outbreaks. Despite this, reports exist of differential susceptibility to viral infection between different shrimp species and populations, and between shrimp and other decapod crustaceans. These reports have, in part, provided the motivation to identify key mechanisms of antiviral resistance, or refractivity, in commercially-important species. Within the last decade these studies have created significant advances in our understanding of host virus interactions in decapod models. However, at the same time, the complexity of host virus interactions has presented significant challenges for interpretation of anti-viral immune responses. In this short review, recent progress in our understanding of the complexity of host virus interactions are considered, and challenges to the unequivocal identification of anti-viral immunity are highlighted. Special consideration is given to the advances in understanding being created by the use of RNA interference approaches. Based on the 'state of the art', it is concluded that the identification of effective intervention strategies for application at farm scale currently presents an unrealistic target for the aquaculture industry. Future technical developments necessary to support continued progress are also considered.

Design and Construction of Shrimp Antiviral DNA Vaccines Expressing Long and Short Hairpins for Protection by RNA Interference.

DNA vaccines present the aquaculture industry with an effective and economically viable method of controlling viral pathogens that drastically affect productivity. Since specific immune response is rudimentary in invertebrates, the presence of RNA interference (RNAi) pathway in shrimps provides a promising new approach to vaccination. Plasmid DNA vaccines that express short or long double stranded RNA in vivo have shown protection against viral diseases. The design, construction and considerations for preparing such vaccines are discussed.

Activation of Vago by interferon regulatory factor (IRF) suggests an interferon system-like antiviral mechanism in shrimp.

There is a debate on whether invertebrates possess an antiviral immunity similar to the interferon (IFN) system of vertebrates. The Vago gene from arthropods encodes a viral-activated secreted peptide that restricts virus infection through activating the JAK-STAT pathway and is considered to be a cytokine functionally similar to IFN. In this study, the first crustacean IFN regulatory factor (IRF)-like gene was identified in Pacific white shrimp, Litopenaeus vannamei. The L. vannamei IRF showed similar protein nature to mammalian IRFs and could be activated during virus infection. As a transcriptional regulatory factor, L. vannamei IRF could activate the IFN-stimulated response element (ISRE)-containing promoter to regulate the expression of mammalian type I IFNs and initiate an antiviral state in mammalian cells. More importantly, IRF could bind the 5'-untranslated region of L. vannamei Vago4 gene and activate its transcription, suggesting that shrimp Vago may be induced in a similar manner to that of IFNs and supporting the opinion that Vago might function as an IFN-like molecule in invertebrates. These suggested that shrimp might possess an IRF-Vago-JAK/STAT regulatory axis, which is similar to the IRF-IFN-JAK/STAT axis of vertebrates, indicating that invertebrates might possess an IFN system-like antiviral mechanism.

Application of a Label-Free Immunosensor for White Spot Syndrome Virus (WSSV) in Shrimp Cultivation Water.

White spot syndrome virus (WSSV) is a major pathogen affecting the shrimp industry worldwide. In a preliminary study, WSSV binding protein (WBP) was specifically bound to the VP26 protein of WSSV. Therefore, we have developed the label-free affinity immunosensor using the WBP together with anti-GST-VP26 for quantitative detection of WSSV in shrimp pond water. When the biological molecules were immobilized on a gold electrode to form a self-assembled monolayer, it was then used to detect WSSV using a flow injection system with optimized conditions. Binding between the different copies of WSSV and the immobilized biological molecules was detected by an impedance change (ΔZ″) in real time. The sensitivity of the developed immunosensor was in the linear range of 1.6 × 10(1)-1.6 × 10(6) copies/µl. The system was highly sensitive for the analysis of WSSV as shown by the lack of impedance change when using yellow head virus (YHV). The developed immunosensor could be reused up to 37 times (relative standard deviation (RSD), 3.24 %) with a good reproducibility of residual activity (80-110 %). The immunosensor was simple to operate, reliable, reproducible, and could be applied for the detection and quantification of WSSV in water during shrimp cultivation.

Characterization of fossilized relatives of the White Spot Syndrome Virus in genomes of decapod crustaceans.

BACKGROUND: The White Spot Syndrome Virus (WSSV) is an important pathogen that infects a variety of decapod species and causes a highly contagious disease in penaeid shrimps. Mass mortalities caused by WSSV have pronounced commercial impact on shrimp aquaculture. Until now WSSV is the only known member of the virus family Nimaviridae, a group with obscure phylogenetic affinities. Its isolated position makes WSSV studies challenging due to large number of genes without homology in other viruses or cellular organisms. RESULTS: Here we report the discovery of an unusually large amount of sequences with high similarity to WSSV in a genomic library from the Jamaican bromeliad crab Metopaulias depressus. De novo assembly of these sequences allowed for the partial reconstruction of the genome of this endogenized virus with total length of 200 kbp encompassed in three scaffolds. The genome includes at least 68 putative open reading frames with homology in WSSV, most of which are intact. Among these, twelve orthologs of WSSV genes coding for non-structural proteins and nine genes known to code for the major components of the WSSV virion were discovered. Together with reanalysis of two similar cases of WSSV-like sequences in penaeid shrimp genomic libraries, our data allowed comparison of gene composition and gene order between different lineages related to WSSV. Furthermore, screening of published sequence databases revealed sequences with highest similarity to WSSV and the newly described virus in genomic libraries of at least three further decapod species. Analysis of the viral sequences detected in decapods suggests that they are less a result of contemporary WSSV infection, but rather originate from ancestral infection events. Phylogenetic analyses suggest that genes were acquired repeatedly by divergent viruses or viral strains of the Nimaviridae. CONCLUSIONS: Our results shed new light on the evolution of the Nimaviridae and point to a long association of this viral group with decapod crustaceans.

A pilot metabolic profiling study in hepatopancreas of Litopenaeus vannamei with white spot syndrome virus based on ¹H NMR spectroscopy.

White spot syndrome virus, which was a pathogen first found in 1992, had emerged globally affecting shrimp populations in aquaculture. Here, we comprehensively analyzed the metabolic changes of hepatopancreas from Litopenaeus vannamei which were infected with white spot syndrome virus by (1)H nuclear magnetic resonance (NMR). Through the NOESYPR1D spectrum combined with multi-variate pattern recognition analysis, including principal component analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLS-DA) models, significantly metabolic changes were observed in WSSV-infected groups compared with the control groups. In the first 48 h, α-glucose and ß-glucose were higher in the WSSV-infected group. Meanwhile, acetate, lactate, N-acetyl glycoprotein signals, lysine, tyrosine and lipid were significantly decreased in the WSSV-infected group. These results suggest that WSSV caused absorption inhibition of amino acids and disturbed protein metabolism as well as cell metabolism in favor of its replication. Our findings could also contribute to further understanding of disease mechanisms.

Stability of the WSSV ORF94 VNTR genotype marker during passage in marine shrimp, freshwater crayfish and freshwater prawns.

The white spot syndrome virus (WSSV) genome contains 3 variable number tandem repeat (VNTR) regions, located in open reading frame (ORF) 75, ORF94 and ORF125, which have been employed for molecular epizootiological studies. A previous report suggested that the ORF 94 VNTR is highly unstable, varying in the number of tandem repeats during single passages from shrimp to other crustaceans. As such rapid variations would have profound implications for the interpretation of molecular epizootiological data, we re-examined the stability of the ORF94 VNTR. Two WSSV isolates with different ORF94 VNTR genotypes (TRS5 and TRS7) were obtained from disease outbreaks in farmed black tiger shrimp Penaeus monodon in Indonesia. High titre stocks of each virus were produced by injection in specific pathogen-free (SPF) Pacific white shrimp Litopenaeus vannamei with filtered infected tissue extracts, and the genotypes were confirmed. Each stock (macerated tissue) was then used to feed SPF Pacific white shrimp, freshwater crayfish (Cherax sp.) and freshwater prawns Macrobrachium rosenbergii through 3 successive passages involving alternative hosts at each level. Taqman real-time PCR was conducted on samples from each group to confirm infection and quantify viral genetic loads. ORF94 VNTR genotype analysis conducted on samples from each of the 43 passage groups indicated no variations in the VNTR number in either genotype TRS5 or genotype TRS7. This finding is contrary to the previous report and suggests that ORF94 VNTR are stable during multiple passages in these crustaceans.

Counter-insurgents of the blue revolution? Parasites and diseases affecting aquaculture and science.

Aquaculture is the fastest-growing segment of food production and is expected to supply a growing portion of animal protein for consumption by humans. Because industrial aquaculture developed only recently compared to industrial agriculture, its development occurred within the context of a growing environmental awareness and acknowledgment of environmental issues associated with industrial farming. As such, parasites and diseases have become central criticisms of commercial aquaculture. This focus on parasites and diseases, however, has created a nexus of opportunities for research that has facilitated considerable scientific advances in the fields of parasitology and aquaculture. This paper reviews Myxobolus cerebralis , Lepeophtheirus salmonis , white spot syndrome virus, and assorted flatworms as select marquee aquaculture pathogens, summarizes the status of the diseases caused by each and their impacts on aquaculture, and highlights some of the significant contributions these pathogens have made to the science of parasitology and aquaculture.

WSSV-induced crayfish Dscam shows durable immune behavior.

One of the major gaps in our understanding of arthropod specific immune priming concerns the mechanism[s] by which the observed long-term (>2 weeks) protective effects might be mediated. Hypervariable Dscam (Down syndrome cell adhesion molecule) might support arthropod innate immunity with specificity for more extended periods. We show here that, in the relatively long-lived arthropod Cherax quadricarinatus, CqDscam does not behave like a typical, immediately-acting, short-lived innate immune factor: CqDscam was not induced within hours after challenge with a lethal virus, but instead was only up-regulated after 2-5 days. This initial response faded within ∼ 2 weeks, but another maximum was reached ∼ 1 month later. At around 2 months after the initial challenge, the virus-induced CqDscam bound to the virus virion and acted to neutralize the virus However, although CqDscam helped crayfish to survive during persistent infection, it nevertheless failed to provide any enhanced protection against a subsequent WSSV challenge. Thus, CqDscam is capable of supporting extended anti-virus immune memory in arthropods. Also, during a persistent virus infection, the balance of "immune firepower" in crayfish appears to be altered such that the general immune factors become depleted while CqDscam becomes relatively predominant.