Epitope mapping of the White Spot Syndrome Virus (WSSV) VP28 monoclonal antibody through combined in silico and in vitro analysis reveals the potential antibody binding site

White Spot Syndrome Virus (WSSV) infecting shrimp is an enveloped double-stranded DNA virus. The WSSV is a member of the genus Whispovirus. The envelope protein VP28 is the most investigated protein of WSSV. In the present study, the epitope mapping of the monoclonal antibody (MAb) C-33 was carried out. Based on the epitope mapping results, an antigen-antibody interaction model was derived. Peptide scanning and confirmation of epitopes of MAb C-33 were carried out using the sequence data. The MAb was reactive to the epitope of both recombinant VP28 and the whole virus. The results of the study indicated the presence of an epitope region. The epitope region is found positioned within two peptides, covering 13 amino acids. Framework and CDR (complementarity determining regions) of heavy and light chain (VH & VL) sequences showed identity to germline immunoglobulin sequences. The Web Antibody Modelling (WAM) selected for further evaluation based on a comparative analysis of WAM and Rosetta server-generated models of the Fv region. The docking study using WAM generated model revealed that the residues from LEU98 to GLY105 are active in antibody binding. The findings of this study could form a structural basis for further research in VP28 based diagnostics and therapeutics or vaccine discovery.

Evaluation of biofilm of Vibrio anguillarum for oral vaccination of Asian seabass, Lates calcarifer (BLOCH, 1790)

The present study evaluated the biofilm (BF) of Vibrio anguillarum for oral vaccination of Asian seabass, Lates calcarifer. An 80-day experiment was carried out in circular fiber-reinforced plastic (FRP) tanks using free cell (FC) and BF of Vibrio anguillarum with triplicate in each. Heat-inactivated FC and BF cells at 10⁷, 10¹⁰ and 10¹³ CFU/g fish/d were fed to fish for 20 days, agglutination antibody titer estimated at each 10 days interval up to 60-day post vaccination. As compared to FC and control there was a significant increase in agglutinating antibody titer in the biofilm vaccinated fishes. Among the 3 doses, BF at 10¹⁰ cfu/g fish/d was considered the ideal dose for vaccination. Relative percentage survival (RPS) was higher in biofilm vaccinated fish (85.4%) compared to that with free cells (27.0%). The study demonstrated the better performance of V. anguillarum biofilm oral vaccine compared that with free cell vaccine in L. calcarifer. The study further supports better performance of biofilm vaccine model with one more bacterial pathogen in a high carnivore fish.

Evaluation of the Sensitivity of the Flow Through Assay for detection of White Spot Syndrome Virus (WSSV) using a cocktail of monoclonal antibodies

A panel of four monoclonal antibodies (C-05, C-14, C-38 and C-56) specific to VP28 of White spot syndrome virus (WSSV) were evaluated individually and in cocktail to increase sensitivity of the Flow Through Assay (FTA) for detection of the virus. Recombinant VP28 and semi purified WSSV was used as antigen for evaluation. Out of the total 11 cocktails and four individual of MAbs, 2 MAb cocktails C-05 + C-56 and C-14 + C-56 exhibited highest sensitivity in the FTA. The two MAb cocktail were 100 times more sensitive than 1-step PCR and nearly equivalent to 2-step PCR for the detection of WSSV. The detection limit of WSSV by MAb cocktail increased by two fold compared to the single MAb C-05 currently being used in (FTA).

Identification of putative genes involved in parasitism in the anchor worm, Lernaea cyprinacea by de novo transcriptome analysis

There is little information on the genome sequence of Lernaea cyprinacea a major ectoparasite of freshwater fish throughout the world. We subjected the L. cyprinacea transcriptome (adult and free living stages) to Illumina HiSeq 2000 sequencing. We obtained a total of 31,671,751 (31.67 millions) reads for the adult parasitic stage and 33,840,446 (33.84 millions) for the free living stage. The reads were assembled into 50,792 contigs for the adult stage and 69,378 for the free living stage. Using the pfam database, 41.91% of the transcriptome was annotated. The transcriptome was mined for genes associated with parasitism. To examine gene expression changes associated with the parasitism of L. cyprinacea during the transit from the free living to parasitic stage, we studied the differentially expressed transcripts between the two stages. The microsatellite markers were also identified (9,843 for adult stage; 16,813 for free living stages) and this would facilitate population genetic studies in various geographical isolates of Lernaea. Our data provides the most comprehensive sequence resource available for L. cyprinacea and demonstrates that Illumina sequencing allows de novo transcriptome assembly and gene expression analysis in a species lacking genome information. The data could open new avenues for a wide array of genetic, evolutionary, biological, ecological, epidemiological studies, and a solid foundation for the development of novel interventions against L. cyprinacea.

Evaluation of biofilm of Aeromonas hydrophila for oral vaccination of Channa striatus

Our laboratory has developed a biofilm oral vaccine of Aeromonas hydrophila, which has given significantly higher antibody agglutination titre and protection in herbivorous carps and omnivorous walking catfish compared to that with free cell vaccine. Against this background, in the present study A. hydrophila biofilm oral vaccine was evaluated in Channa striatus, a carnivorous fish model. The fish was fed with biofilm (BF) and free cell (FC) of A. hydrophila vaccine at 10(10) cells/g fish/day for 20 d. Serum antibody production monitored with a monoclonal antibody based ELISA for 60 day post vaccination. Significantly higher antibody titre was recorded with BF compared to that with FC. Furthermore, BF vaccinated fish upon challenge with A. hydrophila at 10(9) cfu/ml had significantly higher relative per cent survival (88) than that with FC (29.6).

Development of a monoclonal antibody-based flow-through immunoassay (FTA) for detection of white spot syndrome virus (WSSV) in black tiger shrimp Penaeus monodon

A flow-through immunoassay (FTA), an improved version of immunodot, was developed using a nitrocellulose membrane baked onto adsorbent pads enclosed in a plastic cassette to detect white spot syndrome virus (WSSV) in shrimp. Sharp purple dots developed with WSSV against the white background of the nitrocellulose membrane. The detection limits of WSSV by the FTA and immunodot were 0.312 and 1.2 μg mL(-1) crude WSSV protein, respectively. The FTA could be completed in 8-10 min compared with 90 min for immunodot. The FTA was 100 times more sensitive than 1-step polymerase chain reaction (PCR) and in between that of the 1- and 2-step PCR protocol recommended by the Office of International Epizootics (OIE). In experimental, orally infected shrimp post-larvae, WSSV was first detected 14, 16 and 18 h post-infection (hpi) by FTA, immunodot and one-step PCR, respectively. The FTA detected WSSV 2 and 4 h earlier than immunodot and one-step PCR, respectively. The FTA was more sensitive (25/27) than one-step PCR (23/27) and immunodot (23/27) for the detection of WSSV from white spot disease outbreak ponds. The reagent components of the FTA were stable giving expected results for 6 m at 4-8 °C. The FTA is available as a rapid test kit called 'RapiDot' for the early detection of WSSV under field conditions.

Development and standardization of a monoclonal antibody-based rapid flow-through immunoassay for the detection of Aphanomyces invadans in the field

A monoclonal antibody-based flow-through immunoassay (FTA) was developed using a nitrocellulose membrane placed on the top of adsorbent pads enclosed in a plastic cassette with a test zone at the center. The FTA could be completed within 10 min. Clear purple dots against a white background indicated the presence of Aphanomyces (A.) invadans. The FTA limit of detection was 7 μg/mL for A. invadans compared to 56 μg/mL for the immunodot. FTA and polymerase chain reaction (PCR) could detect A. invadans in fish tissue homogenates at a 10(-11) dilution compared to a 10(-8) dilution by immunodot. In fish suffering from natural cases of epizootic ulcerative syndrome (EUS) collected from Mangalore, India, FTA and PCR could detect A. invadans in 100% of the samples compared to 89.04% detected by immunodot. FTA reagents were stable and produced expected results for 4 months when stored at 4~8°C. This rapid test could serve as simple and cost-effective on-site screening tool to detect A. invadans in fish from EUS outbreak areas and in ports during the shipment of live or frozen fish.

Epitope analysis of white spot syndrome virus of Penaeus monodon by in vivo neutralization assay employing a panel of monoclonal antibodies

A panel of six monoclonal antibodies (MAbs) against the major envelope proteins VP18, VP26 and VP28 of white spot syndrome virus (WSSV) was evaluated for neutralization of the virus in vivo in Penaeus monodon. WSSV stock diluted to 1 x 10⁻⁶ resulting in 100% mortality on 12 day post injection (dpi) was used as optimum infectious dose of virus for challenge. Constant quantity (100 μg/ml) of MAbs C-5, C-14, C-33, C-38, C-56 and C-72 was incubated separately with WSSV (1 x 10⁻⁶ dilution) at 27 °C for 90 min and injected to shrimp. WSSV infection was neutralized by the MAbs C-5, C-14 and C-33 with a relative percent survival (RPS) of 60, 80 and 60 on 12 dpi, respectively compared to 100% mortality in positive control injected with WSSV alone. MAbs C-38, C-56 and C-72 could neutralize WSSV infection with RPS on 12 dpi of 40, 30 and 30, respectively. Shrimp injected with WSSV (1 x 10⁻⁶ dilution) incubated with panel of the MAbs at 100 μg/ml separately were subjected to nested PCR analysis at 0, 8, 12, 24, 36, 48 and 72 hour post injection (hpi) to provide further evidence for neutralization. MAbs C-5, C-14 and C-33 showed delay in WSSV positivity by 24 and 48 hpi by 2nd and 1st step PCR, respectively. MAbs C-38, C-56 and C-72 showed WSSV positivity by 12 and 24 hpi by 2nd and 1st step PCR, respectively. Shrimp injected with WSSV alone showed WSSV positivity by 8 and 12 hpi by 2nd and 1st step PCR, respectively. The study clearly shows that infectivity of WSSV could be delayed by MAbs C-14, C-5 and C-33.

Evaluation of immune response and resistance to diseases in tiger shrimp, Penaeus monodon fed with biofilm of Vibrio alginolyticus

Immune response in juvenile tiger shrimp, Penaeus monodon fed with biofilm (BF) and free cells (FC) of Vibrio alginolyticus was studied by evaluating the hemocyte count, phenoloxidase activity and antibacterial activity. The above immune responses were higher in BF fed shrimp than that in FC fed or control shrimp. Among the different doses of BF of V. alginolyticus tested, 10(9) cfu g(-1) shrimp day(-1) for two weeks could evoke higher immune response. BF fed shrimp were more resistant to injection challenge with V. alginolyticus and whitespot syndrome virus (WSSV) with significantly higher RPS compared to that with FC fed and control shrimp. Better resistance was also reflected by rapid clearance of V. alginolyticus and WSSV from the hemolymph as confirmed by immunodot and histopathology.

Isolation and characterization of immunoglobulin of the Indian major carp, rohu [Labeo rohita (Ham.)]

Information on the structure and character of immunoglobulin of fishes is essential in health management. A study was carried out to characterize the serum immunoglobulin (IgM) of the Indian major carp, rohu Labeo rohita (Ham.). Rohu (500g) were immunised with bovine serum albumin (BSA) and the anti-BSA antibody was purified employing BSA-CL agarose affinity column chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) of the purified Ig in a 3% gel under non-reduced conditions revealed a single protein having a molecular weight of 850kDa. Analysis of the purified serum in 10% SDS-PAGE under reduced conditions revealed that the immunoglobulin contained heavy and light chains with molecular weights of 85 and 23kDa, respectively. A polyclonal mouse anti-rohu IgM was prepared and used in an immunodot test which showed a specific reaction of the crude rohu anti-BSA antiserum and the purified anti-BSA IgM with BSA. Results indicate that the immunoglobulin of L. rohita is tetrameric IgM, similar to that of other fishes.

Evaluation of biofilm of Aeromonas hydrophila for oral vaccination of Clarias batrachus--a carnivore model

Biofilm of Aeromonas hydrophila was evaluated for oral vaccination of walking catfish (Clarias batrachus L.). Fish were fed with fish paste incorporating biofilm (BF) or free cells (FC) of A. hydrophila for 20 days and monitored for serum antibody production up to 60 days post-vaccination. Serum agglutinating antibody titre and relative percent survival (RPS) following challenge were found to be significantly higher in catfish fed with BF vaccine compared to that with FC.

Antigen expression in biofilm cells of Aeromonas hydrophila employed in oral vaccination of fish

Total protein, S-layer protein and lipopolysaccharides (LPS) of biofilm cells of Aeromonas hydrophila were analysed by SDS-PAGE and compared with that of planktonic cells. In the whole cell lysate of biofilm cells, about 15 proteins were repressed while three new proteins were expressed compared to that in planktonic cells. Interestingly, in biofilm cells the S-layer proteins were lost and LPS showed an additional high molecular weight band compared to that in planktonic cells. We propose that the change in LPS profile must have contributed to the loss of S-layer. Also, the high molecular weight band of LPS might play a role in the better performance of biofilm oral vaccine by eliciting a protective immune response.

Water quality, biofilm production and growth of fringe-lipped carp (Labeo fimbriatus) in tanks provided with two solid substrates

The effects of two substrates, sugarcane bagasse (T(1)) and paddy straw (T(2)) on water quality and growth of Labeo fimbriatus were studied in mud-bottomed, manured cement tanks, in triplicate; a set of three tanks without substrate served as control (T(3)). Addition of manure and substrate brought about a decrease in dissolved oxygen level, but it stabilized after 15 days, when the tanks were stocked with 30 fish each, fed at 3% body weight daily and reared for 90 days. Total ammonia content in substrate based treatments was relatively lower than in the control. Significantly higher nitrite-nitrogen was recorded in the control tanks. The total plate counts (TPC) of bacteria in water did not differ significantly between treatments and control. The overall mean value of TPC with substrate was higher in T(2) than in T(1). The mean phytoplankton density in water was the highest in T(1), followed by T(3) and T(2), whereas zooplankton density was the highest in T(1) followed by T(2) and T(3). The growth of fish was significantly (P<0.05) higher in substrate-based tanks, the percentage increases over control being 30.44 (T(1)) and 28.71 (T(2)) respectively. Higher RNA, DNA and RNA:DNA ratios were recorded under T(1), followed by T(2) and T(3). Higher enzyme activity was observed in fish from substrate treatments, which was attributable to the additional nutrients derived through the biofilm. The results demonstrated that production of L. fimbriatus can be significantly increased by the introduction of biodegradable substrates into culture systems where fertilization and feeding are employed.

Monoclonal antibodies developed for sensitive detection and comparison of white spot syndrome virus isolates in India

Since its first report in 1994, white spot syndrome virus (WSSV) has become widespread in India. We have developed a simple, rapid and sensitive monoclonal antibody (MAb)-based immunodot test for detection of WSSV. Four MAbs of IgG isotype were produced against an Indian isolate of WSSV: 1 MAb recognised a 28 kDa viral protein while the other 3 recognised both 28 and 18 kDa proteins. The 4 MAbs recognised 4 different Indian WSSV isolates collected at different times from the east and west coasts of India, indicating antigenic uniformity of the isolates. The limit of detection of the immunodot test was 500 pg of the viral protein, which compared well with 1 step PCR and could be used to detect WSSV in shrimp Penaeus monodon with and without gross signs of white spots in the cuticle. Furthermore, the test was rapid (3 h for completion) and is suitable for further development as a simple field kit.

Estimation of prevalence of white spot syndrome virus (WSSV) by polymerase chain reaction in Penaeus monodon postlarvae at time of stocking in shrimp farms of Karnataka, India: a population-based study

White spot disease (WSD) is at present the most serious viral disease affecting cultivated shrimp species globally. The causative agent, white spot syndrome virus (WSSV), is extremely virulent, has a wide host range and can also be transmitted from broodstock to their offspring. The shrimp postlarvae (PL) act as asymptomatic, latent carriers of the virus, and stocking of WSSV-infected PL has been reported as a risk factor for WSD outbreaks in culture ponds. However, there is no population-based study on WSSV prevalence in PL of shrimp. The present manuscript documents the approaches and the results in the estimation of prevalence of WSSV in PL populations of Penaeus monodon at the time of stocking. A maximum of 300 PL from each of the 73 batches of PL stocked at various farms in the west coast of India during September 1999 to January 2000 were tested for the presence of WSSV by 2-step nested PCR. Thirty-six (49%) of the 73 batches tested positive for WSSV either by 1-step alone (3 batches) or after 2-step nested PCR (33 batches). Sub-samples of 5 PL each or 1 PL each tested to quantify the proportion of infected PL within batches showed that WSSV prevalence was very high in 1-step PCR-positive batches and low in 2-step PCR-positive batches. The study also showed that appropriate sampling and sample size were major factors in determining the prevalence of WSSV in PL populations, underlining the need for testing large samples of PL to reduce errors from falsely negative results.

Uptake and processing of biofilm and free-cell vaccines of Aeromonas hydrophila in indian major carps and common carp following oral vaccination--antigen localization by a monoclonal antibody

Uptake and processing of biofilm (BF) and free-cell (FC) vaccines of Aeromonas hydrophila were studied in the Indian major carps catla Catla catla, and rohu Labeo rohita and in the common carp Cyprinus carpio following a single dose oral vaccination of 10(11) CFU g(-1) fish. Fish were sampled at 0.5, 1, 3, 6, 12, 24 h and at 2, 3, 5 and 10 d following vaccination and antigen localization was studied in the gut, kidney and spleen employing monoclonal antibody based immunofluorescence and immunoperoxidase. The general pattern of antigen localization was similar in catla, rohu and common carp. Initially, both the BF and FC antigens were localized in the gut lumen, followed by their uptake by intraepithelial vacuoles and macrophages. Antigen administered orally was also seen in the spleen and kidney. Both BF and FC antigens were detected in the gut lumen of carp within 30 min following oral delivery. However, BF antigen remained in the lumen of the hindgut for 48 h compared to 6 h in the case of FC antigen. In the early stages, BF antigen was localized in the gut epithelial vacuoles while FC antigen was associated with the small macrophages of the hindgut. Antigen localization in spleen and kidney was observed at 3 h and persisted even up to 10 d following oral delivery. In general, there was a distinct difference between BF and FC vaccines in the duration of retention and quantity of uptake in the gut, kidney and spleen.

Histopathology of cultured shrimp showing gross signs of yellow head syndrome and white spot syndrome during 1994 Indian epizootics

Two epizootics of cultured shrimp occurred in India in 1994. The first case of mass mortalities of tiger shrimp Penaeus monodon in July 1994 was very similar to that caused by yellowhead virus (YHV) infection with regard to gross clinical signs, host species and size of shrimp affected, but it was histologically atypical. Very interestingly, intranuclear inclusions typical of a white spot syndrome virus (WSSV) infection were present in shrimp showing gross signs of yellow head syndrome, suggesting a dual infection. The second case of mass mortalities of P. monodon and P. indicus of all age groups and sizes in November 1994 was typical of a WSSV infection, clinically and histopathologically. Densely stained, round intracytoplasmic inclusions typical for YHV infection found in the lymphoid organ and haematopoietic tissue of WSSV-infected shrimp indicated a possible dual infection.

Differentiation of infectious pancreatic necrosis virus isolates by polymerase chain reaction

Infectious pancreatic necrosis virus (IPNV) from lake trout of Cornwall lake (LT-IPNV), from trout of Jasper (Ja-IPNV) and Arctic char of Northwest Territories (AC-IPNV) are the three isolates recorded from western Canada. Two segments (nt 453-674 and nt 1197-1503) from VP2 coding region of RNA of the isolates were amplified by polymerase chain reaction (PCR) for differentiation. Primers for cDNA synthesis and amplification by PCR were chosen from VP2 coding region of RNA of Ja-IPNV. The segment of 453-674 could be amplified in all the three isolates at annealing temperature from 50 to 60 degrees C. However the segment nt 1197-1503 could be amplified only from Jasper and not from AC or LT-INV at primer annealing temperature ranging from 50 degrees-60 degrees C. PCR product could be obtained from the latter two isolates only at Primer annealing temperature of 45 degrees C. This difference in annealing temperature in PCR amplification between the isolates could be used for differentiating the isolates at genome level.