Protection of Penaeus monodon against white spot syndrome virus by inactivated vaccine with herbal immunostimulants

Experimental Infection Models and Their Usefulness for White Spot Syndrome Virus (WSSV) Research in Shrimp

White spot syndrome virus (WSSV) is marked as one of the most economically devastating pathogens in shrimp aquaculture worldwide. Infection of cultured shrimp can lead to mass mortality (up to 100%). Although progress has been made, our understanding of WSSV's infection process and the virus-host-environment interaction is far from complete. This in turn hinders the development of effective mitigation strategies against WSSV. Infection models occupy a crucial first step in the research flow that tries to elucidate the infectious disease process to develop new antiviral treatments. Moreover, since the establishment of continuous shrimp cell lines is a work in progress, the development and use of standardized in vivo infection models that reflect the host-pathogen interaction in shrimp is a necessity. This review critically examines key aspects of in vivo WSSV infection model development that are often overlooked, such as standardization, (post)larval quality, inoculum type and choice of inoculation procedure, housing conditions, and shrimp welfare considerations. Furthermore, the usefulness of experimental infection models for different lines of WSSV research will be discussed with the aim to aid researchers when choosing a suitable model for their research needs.

Unveiling the anti-inflammatory potential of Acalypha indica L. and analyzing its research trend: digging deep to learn deep

The plant Acalypha indica L. is a well-known traditional plant belonging to the family Euphorbiaceae. Traditional practices of the plant claim to treat asthma, pneumonia, wound healing, rheumatoid arthritis, bronchitis, and skin disorders. The major phytochemicals reported are cyanogenic glucosides, tannins, coumarins, flavonoid glycosides, fatty acids, and volatile oils. To summarize the anti-inflammatory potential of Acalypha indica extract and its phytochemicals through preclinical studies. The search terms include anti-inflammatory, Acalypha indica, and Acalypha indica extract independently or in combination with pro-inflammatory markers using various databases, including Scopus, Web of Science, PubMed, ProQuest, and Google Scholar. The results of preclinical studies confirm that Acalypha indica exhibits strong anti-inflammatory activity. Most of the experimental studies that have been conducted on plant extract are protein denaturation, human red blood cell membrane stabilization assay, and carrageenan-induced inflammation models. However, the molecular mechanism in these studies is still unclear to demonstrate its anti-inflammatory effects. Acalypha indica possesses anti-inflammatory effects that may be due to the presence of phenolic compounds especially flavonoids present in the Acalypha indica. Thus, further research is needed, to understand mechanistic insights of the plant phytochemicals to represent anti-inflammatory properties.

Dietary supplementation of Salvinia cucullata in white shrimp Litopenaeus vannamei to enhance the growth, nonspecific immune responses, and disease resistance to Vibrio parahaemolyticus

The current study investigates the effect of ethanolic extract of Salvinia cucullata (EESC) on growth, non-specific immune parameters, and disease resistance to Vibrio parahaemolyticus in Litopenaeus vannamei. The in-vitro cytotoxicity investigation was performed on shrimp hemolymph hemocytes to assess the toxicity and immunological responses with various concentrations of EESC, and no significant difference in cell viability was seen across dosages, but substantial changes in Phenol Oxidase (PO) and phagocytosis were reported. The in-vivo investigation was conducted on white shrimp for 56 days using varied amounts of 0 (control), 5 (EESC5), 10 (EESC10), and 20 (EESC20) g kg^-1 containing feeds and challenged against Vibrio parahaemolyticus. The shrimp fed the EESC10 diet gained the most weight, had the highest specific growth rate (SGR) and had a better feed conversion ratio (FCR). The highest cumulative survival percentage was noted on the EESC10 diet-fed shrimps followed by EESC20 and EESC5 groups after the bacterial challenge with V. parahaemolyticus. The results of immune parameters such as total protein, total carbohydrate, coagulation time, total hemocytes count (THC), superoxide dismutase (SOD), ProPO, and phagocytosis levels were better in the EESC10 group. EESC5 and EESC20 groups were also shown better immunomodulatory effects than the control group. In conclusion, the oral administration of EESC was found to be an effective functional feed additive to improve the growth, immune parameters, and disease resistance against V. parahaemolyticus in L.vannamei.

Effect of mangrove leaf extract (Acanthus ilicifolius) on non-specific immune status and vibriosis resistance of black tiger shrimps (Penaeus monodon) challenged with Vibrio harveyi

Background and Aim

There has been continuous effort to search for alternative medicinal plants that are applicable to ameliorate viral disease on shrimp pond. This study aimed to examine the effect of Acanthus ilicifolius leaf extract on clinical symptoms and non-specific immune response of black tiger shrimp (Penaeus monodon).

Materials and Methods

A total of 330 shrimps were equally assigned into three extract forms (crude extract, ethyl acetate extract, and n-butanol extract, respectively) in which three levels were provided for each extract. Negative control (without leaf extract) and positive control (with oxytetracycline at 0.05 mg/mL) were used, giving a total of 11 experimental treatments.

Results

The results showed that shrimps induced into all form of leaf extracts had significantly higher survival rates, clinical symptoms, and pathological anatomy than those negative control (C-) and positive control (C+). Total hemocyte cells, granulocytes, percentage of phagocytic, and prophenoloxidase activity were similar among leaf extract treatments (p>0.05), but those groups were significantly higher than those of C- and C+ (p<0.05).

Conclusion

n-butanol leaf extract at 300 mg/L is suggested to be the most effective treatment since it showed the highest efficacy on the parameters observed. Thus, it is possible to use the leaf extract of A. ilicifolius on-farm as a strategy to enhance bacterial disease resistance and prevent mortality.

Identification of antigenic domains and peptides from VP15 of white spot syndrome virus and their antiviral effects in Marsupenaeus japonicus

White spot syndrome virus (WSSV) is one of the most devastating pathogens in penaeid shrimp and can cause massive damage in shrimp aquaculture industries. Previously, the WSSV structural protein VP15 was identified as an antigenic reagent against WSSV infections. In this study, we truncated this protein into VP15_(1–25), VP15_(26–57), VP15_(58–80), and VP15_{(1–25,58–80)}. The purified proteins from the E. coli expression system were assayed as potential protective agents in Kuruma shrimp (Marsupenaeus japonicus) using the prime-and-boost strategy. Among the four truncated constructs, VP15_(26–57) provided a significant improvement in the shrimp survival rate after 20 days of viral infection. Subsequently, four peptides (KR11, SR11, SK10, and KK13) from VP15_(26–57) were synthesized and applied in an in vivo assay. Our results showed that SR11 could significantly enhance the shrimp survival rate, as determined from the accumulated survival rate. Moreover, a multiligand binding protein with a role in the host immune response and a possible VP15-binding partner, MjgC1qR, from the host M. japonicus were employed to test its binding with the VP15 protein. GST pull-down assays revealed that MjgC1qR binds with VP15, VP15_(26–57), and SR11. Taken together, we conclude that SR11 is a determinant antigenic peptide of VP15 conferring antiviral activity against WSSV.

Effects of Fermented Kefir as a Functional Feed Additive in Litopenaeus vannamei Farming

Litopenaeus vannamei, known as whiteleg shrimp, is susceptible to infection by pathogenic microorganisms such as viruses and bacteria. Therefore, the prevention of infections in this shrimp is important to regulate the outbreaks of pathogenic microorganisms. In this study, we investigated the effects of kefir as a functional feed additive on innate immunity, survival against WSSV (White Spot Syndrome Virus) and productivity of L. vannamei. As a result, the treatment of kefir could upregulate six of seven genes crucial for innate immunity of L. vannamei. Also, the treatment of kefir directly improved the survival rate of L. vannamei against WSSV infection. Finally, in order to determine whether kefir can improve the productivity of shrimp, we carried out field tests in three aquaculture farms in South Korea. The weight of shrimp fed kefir was increased by 120% as well as the length, compared with that of the control group. These results demonstrate that kefir can be utilized as a functional feed additive to improve both innate immunity and productivity of L. vannamei in shrimp farming with no use of antibiotics.

Identification and functional characterization of a novel C-type lectin from the kuruma shrimp, Marsupenaeus japonicus

C-type lectins (CTLs) are immune molecules that are crucial to the invertebrate innate immune system with the primary function of recognizing invading pathogens. In the present study, a novel CTL was cloned from Marsupenaeus japonicus (MjCTL), and its tissue distribution and expression patterns over time in response to white spot syndrome virus (WSSV) and Vibrio parahaemolyticus were further investigated. The open reading frame (ORF) of MjCTL was 513 bp and encoded a polypeptide of 170 amino acids, which contained a signal peptide and a carbohydrate recognition domain (CRD) that are typical for CTLs. MjCTL was primarily expressed in the hepatopancreas and weakly expressed in hemocytes, gill, stomach, intestine, heart, muscle and eyestalk. The expression level of MjCTL in the hepatopancreas was dramatically increased at 48 h post-injection with WSSV at a dosage of 1 × 10⁵ virions. Glutathione-S-transferase (GST) pull-down assays showed that MjCTL could directly bind to several WSSV envelope proteins, including VP19, VP24, VP26 and VP28. Moreover, MjCTL displayed antibacterial activity against V. parahaemolyticus. Our results indicated that MjCTL exhibited multiple functions in innate immune response against pathogens.

In vivo and in vitro antimicrobial activity of phytol, a diterpene molecule, isolated and characterized from Adhatoda vasica Nees. (Acanthaceae), to control severe bacterial disease of ornamental fish, Carassius auratus, caused by Bacillus licheniformis PKBMS16

Bacillus licheniformis, a pathogenic new strain of bacteria is considered as the main cause of high mortalities and economic losses among the ornamental fish farms of India. The present study aimed to investigate the anti-bacterial and Immunostimulant activity of three selected Indian medicinal plants, Allium sativum, Adhatoda vasica and Centella asiatica for treating Bacillus licheniformis PKBMS₁₆ by subsequent experimental and clinical trials using different organic polar and non-polar solvents. The antimicrobial and Immunostimulant activity of methanolic crude extracts of Adhatoda vasica was fractions and active constituents was further characterized by chromatography and mass spectroscopy studies using FTIR, ¹HNMR and ^13c NMR to identify as well as to determine the nature of the pure compound which is phytol (C₂₀H₄₀O), a diterpene alcohol with a molecular weight of m/z 297. In order to study the in vivo anti-pathogenic influence of the biologically active compounds, phytol were incorporated to the artificial diets at the concentration of 2, 5 and 8 mg/kg and fed to the1.0 × 10⁵ CFU/ml of Bacillus licheniformis PKBMS₁₆ injected experimentally challenged ornamental goldfish Carassius auratus for twenty days. Phytol treated group significantly (P < 0.01 and P < 0.05) reduced the rate of fish mortality. After the termination of survivability assay the estimation of hemato-biochemical parameters have been performed and revealed the significant recovery of health condition on 20th days post treatment. Therefore, the present study concluded that the low toxicity along with high bioactivity and tolerance by lower vertebrate supports the potential of phytol as a new compound for inducing fish immunity.

Molecular Identification of Vibrio alginolyticus Causing Vibriosis in Shrimp and Its Herbal Remedy

Penaeus monodon is highly susceptible to vibriosis disease. Aims of the study were to identify the pathogen causing vibriosis in P. monodon through molecular techniques and develop a biocontrol method of the disease by application of herbal extracts. Shrimp samples were collected aseptically from the infected farm and the bacteria were isolated from the infected region of those samples. Based on phenotypic identification, several isolates were identified as Vibrio sp. 16S rRNA gene sequences of the selected isolates exhibited 100% homology with V. alginolyticus strain ATCC 17749. An in vivo infection challenge test was performed by immersion method with V. alginolyticus where these isolates caused high mortality in juvenile shrimp with prominent symptoms of hepatopancreatic necrosis. Antibiogram profile of the isolates was determined against eleven commercial antibiotic discs whereas the isolates were found resistant to multiple antibiotics. A total of twenty-one herbal extracts were screened where Emblica officinalis, Allium sativum, and Syzygium aromaticum strongly inhibited the growth of V. alginolyticus in in vitro conditions. In in vivo conditions, the ethyl acetate extracts of E. officinalis and A. sativum successfully controlled the vibriosis disease in shrimp at a dose of 10 mg/g feed. This is the first report on molecular identification and biocontrol of V. alginolyticus in shrimp in Bangladesh.

Penaeus monodon is highly susceptible to vibriosis disease. Aims of the study were to identify the pathogen causing vibriosis in P. monodon through molecular techniques and develop a biocontrol method of the disease by application of herbal extracts. Shrimp samples were collected aseptically from the infected farm and the bacteria were isolated from the infected region of those samples. Based on phenotypic identification, several isolates were identified as Vibrio sp. 16S rRNA gene sequences of the selected isolates exhibited 100% homology with V. alginolyticus strain ATCC 17749. An in vivo infection challenge test was performed by immersion method with V. alginolyticus where these isolates caused high mortality in juvenile shrimp with prominent symptoms of hepatopancreatic necrosis. Antibiogram profile of the isolates was determined against eleven commercial antibiotic discs whereas the isolates were found resistant to multiple antibiotics. A total of twenty-one herbal extracts were screened where Emblica officinalis, Allium sativum, and Syzygium aromaticum strongly inhibited the growth of V. alginolyticus in in vitro conditions. In in vivo conditions, the ethyl acetate extracts of E. officinalis and A. sativum successfully controlled the vibriosis disease in shrimp at a dose of 10 mg/g feed. This is the first report on molecular identification and biocontrol of V. alginolyticus in shrimp in Bangladesh.

Macrobrachium rosenbergii nodavirus (MrNV)-CP-RNA-2 DNA vaccine confers protective immunity in giant freshwater prawn Macrobrachium rosenbergii against MrNV infection

Macrobrachium rosenbergii Nodavirus (MrNV) causes white tail disease (WTD) in Giant freshwater prawn Macrobrachium rosenbergii which leads to immense economic losses in hatcheries and farms. In the present study, we cloned the capsid protein gene of MrNV-CP-RNA-2 (1146 bp) into a DNA vaccine vector pVAX1 to form MrNV-CP-RNA-2- pVAX1. The bacterial transformant, containing the MrNV-CP gene, was coated on the fish diet pellets and fed to juvenile M. rosenbergii for 40 days. After the vaccine delivery, group of M. rosenbergii were challenged with virulent MrNV on 20 and 40^th days post-vaccination (dpv) respectively and monitored for the survival. The non-vaccinated M. rosenbergii succumbed to death (100%) within 5 days, whereas the MrNV-CP-RNA-2- pVAX1 treated groups had the survivals of 60 and 80% in 20 and 40 dpv respectively (P ≤ 0.001). To study the MrNV infection level, double step PCR was performed at different dpv. The results revealed that in 20 dpv group, the infection was decreased to 65% and in 40 dpv group the infection decreased to 69% from control diet fed prawns (P < 0.001). Haematological parameters like coagulation time, total haemocyte count (THC) and oxyhaemocyanin levels were performed for the control and vaccinated prawns. The vaccination helped to decrease the time of coagulation, improved THC and oxyhaemocyanin levels at a significant level (p < 0.001) when compared to the non-vaccinated group. The immunological parameters like prophenol oxidase (ProPO), superoxide anion and intra-agar lysozyme activity were also performed and the results revealed that the level of proPO, superoxide anion and lysozyme activities were significantly (P ≤ 0.05) increased in 20 and 40 dpv groups respectively, when compared with the non-vaccinated groups. Based on the vaccination trials, the DNA vaccine construct MrNV-CP-RNA-2-pVAX1 effectively improved the survival against MrNV challenge, helped to decrease viral load and enhanced the immune system to protect the prawn from MrNV infection. This vaccine construct is highly useful to protect the M. rosenbergii from MrNV infection.

Effect of Argemone mexicana active principles on inhibiting viral multiplication and stimulating immune system in Pacific white leg shrimp Litopenaeus vannamei against white spot syndrome virus

Argemone mexicana called as Mexican prickly poppy is a species of poppy found in Mexico and now widely naturalized in many parts of the world with broad range of bioactivities including anthelmintic, cures lepsory, skin-diseases, inflammations and bilious fevers. Plant parts of A. mexicana were serially extracted with hexane, ethyl acetate, methanol and performed antiviral and immunostimulant screening against WSSV and Vibrio harveyi respectively. The control groups succumbed to death 100% within three days, whereas the mortality was significantly (P < 0.5) reduced to 17.43 and 7.11 in the ethyl acetate extracts of stem and root treated shrimp group respectively. The same trend was reflected in the immunostimulant screening also. Different diets were prepared by the concentrations of 100 (AD-1), 200 (AD-2), 300 (AD-3) and 400 (AD-4) mg kg^-1 using A. mexicana stem and root ethyl acetate extracts and fed to Pacific white leg shrimp Litopenaeus vannamei weighed about 9.0 ± 0.5 g for 30 days. The control groups fed with the normal diets devoid of A. mexicana extracts. The antiviral screening results revealed that, the ethyl acetate extract of the stem and root were effectively suppressed the WSSV and it reflected in the lowest cumulative mortality of treated shrimps. After termination of feeding trials, group of shrimps from control and each experimental group were challenged with virulent WSSV by intramuscular (IM) injection and studied cumulative mortality, molecular diagnosis by quantitative real time PCR (qRT-PCR), biochemical, haematological and immunological parameters. Control group succumbed to 100% death within four days, whereas the survival was significantly (P < 0.001) increased to 30, 45, 75 and 79% in AD1, AD-2, AD-4 and AD-5 diets fed shrimp groups respectively. qRT PCR results with positive correlation analysis revealed that, the WSSV copies were gradually decreased when increasing the A. mexicana extracts in the diets. The highest concentrations (300 and 400 mg g^-1) of A. mexicana extracts in the diets helped to reduce the protein level significantly (P < 0.05) after WSSV challenge. The diets AD-3 and AD-4 also helped to decrease the coagulation time of maximum 64-67% from control groups and maintained the normal level of total haemocyte, oxyhaemocyanin level after WSSV challenge. The proPO level was significantly increased (Column: F = 35.93; P ≤ 0.001 and Row: F = 37.14; P ≤ 0.001) in the AD1-AD-4 diet fed groups from the control diet fed groups. The lowest intra-agar lysozyme activity of 1.63 mm found in control diet fed group and the activity were significantly (P < 0.05) increased to 4.86, 7.89, 9.12 and 10.45 mm of zone of inhibition respectively in AD1 to AD4 diet fed groups.

What vaccination studies tell us about immunological memory within the innate immune system of cultured shrimp and crayfish

The possibility of immunological memory in invertebrates is a topic that has recently attracted a lot of attention. Today, even vertebrates are known to exhibit innate immune responses that show memory-like properties, and since these responses are triggered by cells that are involved in the innate immune system, it seems that immune specificity and immune memory do not necessarily require the presence of B cells and T cells after all. This kind of immune response has been called "immune priming" or "trained immunity". In this report, we review recent observations and our current understanding of immunological memory within the innate immune system in cultured shrimp and crayfish after vaccination with live vaccine, killed vaccine and subunit vaccines. We also discuss the possible mechanisms involved in this immune response.

A multiplex bead-based assay for immune gene expression analysis in shrimp

Here, we developed a 9-plex bead-based array as a tool to evaluate molecular effects on transcription levels of immune-related genes in the black tiger shrimp (Penaeus monodon). The bead array technology allows simultaneous detection of multiple target genes in a single sample, reducing time, labor and cost. The oligonucleotide probes were designed to target eight immune-related genes that involve in antimicrobial activity, melanization, pathogen pattern recognition proteins, lysozyme and one housekeeping gene as an internal control. The nine probes were coupled to carboxylated-magnetic bead sets. The 9-plex PCR primers were designed and optimized for conditions to allow multiplex detection. The specificity of the assay was validated and the sensitivity was determined to be 10³ copies/μL for all target genes. The 9-plex immune gene expression assay was applied to determine transcript levels in gills of P. monodon under exposure to a shrimp pathogen, Vibrio harveyi, and gene expression patterns were consistent to patterns observed under a traditional realtime PCR method. While realtime PCR method gave a better sensitivity but limited multiplexity, our 9-plex immune gene expression assay was able to simultaneously measure expression of multiple target genes, providing useful alternative assay in the need of higher-throughput gene expression analysis such as evaluation of immune stimulatory effects in different feed additives under various dosages and time points in shrimp.

Antibacterial function of herbal extracts on growth, survival and immunoprotection in the black tiger shrimp Penaeus monodon

This study examined the effects of an herbal extract composed of nine herbs i.e Aloe vera, Andrographis pariculata, Annona squamosa, Azadirachta indica, Citrus aurantifolia, Coriandrum sativum, Ocimum sanctum, Ollium cepa and Psidium guajava on growth, survival rate and immunoprotection against pathogenic Vibrio harveyi in the tiger shrimp Penaeus monodon. The petroleum ether, methanol and N-hexen extracts of different herbal plants were selected, processed and thoroughly mixed in equal proportions and added to the shrimp diets at a concentration of 1.0, 2.5 and 5.0 mL kg^-1. After 60 days of feeding, shrimps were challenged with V. harveyi bacteria (1 × 10⁷ cells mL^-1), which were isolated and propagated from the infected shrimps. The shrimps fed on diets with methanolic extraction of 2.5 mL kg^-1 had significantly (P < 0.001) higher survival rate (76%), specific growth rate (4.26 ± 0.11%) and better food conversion ratio (1.5) than the other groups. This study indicates that addition of methanolic herbal extracts of 2.5 mL kg^-1 can positively influence the immune response of tiger shrimp against V. harveyi infection.

Emilia sonchifolia extract activity against white spot syndrome virus and yellow head virus in shrimp cell cultures

Emilia sonchifolia (L.) DC is a plant used in traditional medicine to treat several viral and bacterial diseases. The antiviral activities of selected Sephadex LH-20 column fractions and HPLC subfractions of an acetone extract of E. sonchifolia leaves were determined in shrimp Penaeus merguiensis primary lymphoid cells infected with either white spot syndrome virus (WSSV) or yellow head virus (YHV). WSSV and YHV replication was quantified using quantitative real-time PCR tests targeted to the VP19 and ORF1b gene transcripts, respectively. In lymphoid organ cells exposed to 100 µg ml⁻¹ of either the Sephadex fraction F14 or the HPLC F14 subfraction SF4, both fractions caused reduced replication, but YHV replication was reduced only by SF4. In the asthiazolyl blue mitochondrial enzyme activity assays to assess extract cytotoxicity, >60% of primary lymphoid organ cells remained viable following exposure to 100 µg ml⁻¹ of either F14 or SF4. GC-MS analysis of the HPLC F14 subfraction SF4 showed that it contained 2,4-di-tert-butylphenol. This study is the first to show that E. sonchifolia leaf extracts might be useful as bioactive agents to protect shrimp against viruses such as WSSV and YHV.

Dietary administration of Gynura bicolor (Roxb. Willd.) DC water extract enhances immune response and survival rate against Vibrio alginolyticus and white spot syndrome virus in white shrimp Litopeneaus vannamei

Gynura bicolor (Roxb. & Willd.) DC., a perennial plant belonging to the Asteraceae family, is originated from the tropical area of Asia. The total hemocyte count (THC), phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, and lysozyme activity were examined after white shrimp Litopenaeus vannamei had been fed diets containing the water extract of G. bicolor at 0 (control), 0.5, 1.0, and 2.0 g (kg diet)(-1) for 7-28 days. The results indicated that these parameters increased accordingly with the amount of extract and time. THCs of the shrimp fed the G. bicolor diets at 1.0 and 2.0 g (kg diet)(-1) were significantly higher than that fed the control diet for 14-28 days. For the shrimp fed the G. bicolor diets at 0.5, 1.0, and 2.0 g (kg diet)(-1), the PO, RBs, and lysozyme activities reached the highest levels after 7 days, whereas SOD activity reached the highest levels after 14 days. In a separate experiment, white shrimp L. vannamei fed the diets containing the G. bicolor extract for 28 days were challenged with Vibrio alginolyticus at 3 × 10(6) cfu shrimp(-1) and white spot syndrome virus (WSSV) at 1 × 10(3) copies shrimp(-1). The survival rate of the shrimp fed the G. bicolor diets was significantly higher than that of the shrimp fed the control diet at 48-144 h post challenge V. alginolyticus and WSSV. For the shrimp fed the G. bicolor diets at 0.5, 1 and 2 g (kg diet)(-1) under challenges of V. alginolyticus and WSSV, their LPS- and β-1,3-glucan-binding protein (LGBP) and peroxinectin (PE) mRNA expressions were significantly higher than those of the challenged control shrimp at 12-96 and 24-144 h post-challenge, respectively. We concluded that dietary administration of a G. bicolor extract could enhance the innate immunity within 28 days as evidenced by the increases in immune parameters (PO, RBs, and lysozyme) and antioxidant enzyme (SOD) activities of shrimp to against V. alginolyticus and WSSV infections.

Influence of Agathi grandiflora active principles inhibit viral multiplication and stimulate immune system in Indian white shrimp Fenneropenaeus indicus against white spot syndrome virus infection

Five herbs including Adathoda vasica, Agathi grandiflora, Leucas aspera, Psoralea corylifolia, and Quercus infectoria were selected to screen the antiviral and immunostimulant activity against white spot syndrome virus (WSSV) and Vibrio harveyi respectively using different organic polar and non-polar solvents. Based on the initial screening results, ethyl acetate and methanolic extracts of A. grandiflora had strong antiviral and immunostimulant activities. Those extracts incubated with WSSV injected Fenneropenaeus indicus got only 20% mortality and no PCR positive signals were seen in two step PCR amplification. The methanolic extracts of A. grandiflora were further purified through silica column chromatography and the fractions screened again for antiviral and immunostimulant activity. The secondary screening results revealed that, the fractions of F5 to F7 had effectively controlled the WSSV multiplication and V. harveyi growth. The pooled fractions (F5 to F7) was structurally characterized by gas chromatograph-mass spectrometry (GC-MS) analysis and few compounds were identified including 3,7.11,15-Tetramethyl-2-Hexane-1-ol, pytol and 1,2-Benzenedicarboxylic acid, diisooctyl ester. The pooled fractions were mixed with the basal feed ingredients at the concentration of 100 (D-1), 200 (D-2), 300 (D-3) and 400 (D-4) mg kg(-1) and the diets fed to the F. indicus (9.0 ± 0.5 g) for 30 days. After the completion of feeding trail, they were challenged with virulent WSSV and studied the cumulative mortality, molecular diagnosis by quantitative real time PCR (qRT-PCR), biochemical, haematological and immunological parameters. The control diet fed F. indicus succumbed to death 100% within 3 days whereas the D-3 and D-4 helped to reduced the cumulative mortality of 60-80% respectively. The qRT-PCR revealed that, the WSSV copy number was gradually decreased when increasing concentration of A. grandiflora extract active fraction in the diets. The diets D-3 and D-4 helped to reduce the protein and carbohydrate levels significantly (P < 0.01) from the control diet fed groups. Moreover these diets help to decrease the coagulation time of maximum 61% from control groups and improve the total haemocyte count of maximum 51.82 × 10(5) cells ml(-1) in D4 diet fed F. indicus. Finally immunological parameters including prophenol oxidase (proPO) activity, intracellular superoxide anion production and intra-agar lysozyme activity was significantly (P ≤ 0.001) improved in the D-3 and D-4 fed F. indicus after WSSV challenge.

Protection of ornamental gold fish Carassius auratus against Aeromonas hydrophila by treating Ixora coccinea active principles

Herbals such as Ixora coccinea, Daemia extensa and Tridax procumbens were selected to screen in vitro antibacterial and immunostimulant activity against the freshwater fish pathogen Aeromonas hydrophila using different organic polar and non-polar solvents. Initial screening results revealed that, ethyl acetate extracts and its purified fraction of I. coccinea was able to suppress the A. hydrophila strains at more than 15 mm of zone of inhibition and positive immunostimulant activity. The purified active fraction, which eluted from H40: EA60 mobile phase was structurally characterized by GC-MS analysis. Two compounds such as Diethyl Phthalate (1,2-Benzene dicarboxylic acid, monobutyl ester) and Dibutyl Phthalate were characterized using NIST database search. In order to study the in vivo immunostimulant influence of the compounds, the crude extracts (ICE) and purified fractions (ICF) were incorporated to the artificial diets at the concentration of 400 mg kg⁻¹ and fed to the ornamental gold fish Carassius auratus for 30 days. After termination of feeding experiment, they were challenged with highly virulent A. hydrophila AHV-1 which was isolated from infected gold fish and studied the survival, specific bacterial load reduction, serum biochemistry, haematology, immunology and histological parameters. The control diet fed fishes succumbed to death within five days at 100% mortality whereas ICE and ICF fed groups survived 60 and 80% respectively after 10 days. The diets also helped to decrease the Aeromonas load after challenge and significantly (P ≤ 0.01) improved the serum albumin, globulin and protein. The diets also helped to increase the RBC and haemoglobin level significantly (P ≤ 0.05) from the control group. Surprisingly the immunological parameters like phagocytic activity, serum bactericidal activity and lysozyme activity were significantly increased (P ≤ 0.001) in the experimental diets. Macrophages and erythrocytes were abundantly expressed in the treated groups and the present work concluded that, the Phthalate derivatives from I. coccinea helps to stimulate the immune system against A. hydrophila challenge in C. auratus.

Application of bacterial lipopolysaccharide to improve survival of the black tiger shrimp after Vibrio harveyi exposure

This study investigates an effect of bacterial lipopolysaccharide (LPS) as feed supplement to improve immunity of the black tiger shrimp (Penaeus monodon). LPS was coated to commercial feed pellets and given to the shrimp once or twice a day for 10 days before an exposure with shrimp pathogenic bacterium Vibrio harveyi. The growth rates, percent weight gains, total hemocyte and granulocyte counts and survival rates of shrimp between the LPS-coated pellet fed groups and a control group where shrimp fed with commercial feed pellets were compared. After 10 days of the feeding trials, growth rates were not significantly different in all groups, suggesting no toxicity from LPS supplement. To determine beneficial effect of LPS diets, each group was subsequently exposed to V. harveyi by immersion method and the survival rates were recorded for seven days after the immersion. Regardless of the dosages of LPS, the shrimp groups fed with LPS-coated pellets showed higher survival rates than the control group. There was no significant difference in survival rates between the two LPS dosages groups. In addition to survival under pathogen challenge, we also determine effect of LPS on immune-related genes after 10-day feeding trial. Gene expression analysis in the P. monodon intestines revealed that antilipopolysaccharide factor isoform 3 (ALF3), C-type lectin, and mucine-like peritrophin (mucin-like PM) were expressed significantly higher in a group fed with LPS supplemental diet once or twice a day than in a control group. The transcript levels of C-type lectin and mucin-like PM had increased significantly when LPS was given once a day, while significant induction of ALF3 transcripts was observed when shrimp were fed with LPS twice a day. The up-regulation of the immune gene levels in intestines and higher resistance to V. harveyi of the shrimp fed with LPS provide the evidence for potential application of LPS as an immunostimulant in P. monodon farming.

Ingestion of bacteria expressing dsRNA triggers specific RNA silencing in shrimp

RNAi activation in shrimp through dsRNA injection has been well demonstrated but oral delivery of dsRNA remains controversial. Therefore, this study was conducted to determine whether RNAi was induced in shrimp by ingestion of bacteria expressing dsRNA. We fed shrimp, Penaeus monodon and Litopenaeus vannamei, with inactivated bacteria expressing dsRNA specific to the shrimp genes (Rab7 and STAT). Forty-eight hours after 6 day-continuous feeding, the level of the targeted gene transcript was measured by semi-quantitative RT-PCR. Significant reduction of Rab7 as well as STAT transcript was observed when compared to that of control shrimp fed with bacteria containing the empty vector or bacteria expressing non-related dsRNA (GFP). Moreover, the suppression was detected not only in the hepatopancreas but also in the gills indicating the successful systemic induction of RNAi via oral delivery of dsRNA. Our results suggested that RNAi in shrimp could be triggered by ingestion of dsRNA expressing bacteria. Therefore, oral feeding is a practical approach which can be used to deliver dsRNA for further viral inhibition in farmed shrimp.