Efficacy of a Eudragit L30D-55 encapsulated oral vaccine containing inactivated bacteria (Lactococcus garvieae/Streptococcus iniae) in rainbow trout (Oncorhynchus mykiss)

Stability characterizations of feed-based bivalent vaccine containing inactivated Streptococcus agalactiae and Aeromonas hydrophila against streptococcosis and Aeromonas infections in red hybrid tilapia (Oreochromis sp.)

Feed-based bivalent vaccine (FBBV) containing killed whole organism (KWO) of Streptococcus agalactiae and Aeromonas hydrophila with 10% palm oil was previously proved to improve red hybrid tilapia's (Oreochromis sp.) immunity against streptococcosis and Aeromonas infections. This study characterized the FBBV's stability following the preparatory process and storage. The FBBV was prepared, and the KWO's stability was determined microscopically and molecularly. The efficacy of FBBV stored at room temperature (25 ± 2 °C) for 0, 30 and 60 days was investigated in red hybrid tilapia. The results indicated the addition of palm oil was not affecting the KWO's structure and helping in the FBBV's pelletization. In 1 g of FBBV contained 1.5 × 109 CFU/g of S. agalactiae and 4.9 × 109 CFU/g of A. hydrophila, respectively, even after 60 days of storage at room temperature. The KWO's structure in FBBV was not affected following in vitro acidic tolerance analysis, as noted from light and electron microscopies. The FBBV's carbohydrate, energy, moisture, total protein and total ash contents remained stable at 95% after 60 days of storage at room temperature, while the KWO's concentration was slightly reduced to 83.3% for S. agalactiae (1.25 × 109 CFU/g) and 80.6% for A. hydrophila (3.85 × 109 CFU/g), respectively. Fish vaccinated with FBBV that was stored for 0, 30 and 60 days did not show any significant differences (p ≥ 0.05) in the relative percent survival when challenged with pathogenic Streptococcus spp. and Aeromonas spp. These findings suggested that the FBBV is a stable vaccine, which underscores its potential application as aquatic vaccines in aquaculture.

Effect of killed autogenous polyvalent vaccines against Vibrio harveyi, V. alginolyticus and Streptococcus iniae on survival and immunogenicity of Asian seabass (Latescalcarifer)

Vibriosis and Streptococcosis are the most important bacterial diseases that infect Asian seabass (Lates calcarifer) in various stages of its life cycle. Vaccination is a cost-effective strategy to prevent the occurrence of infectious diseases and increase sustainability in the aquaculture industry. This study was aimed to develop and evaluate a killed polyvalent vaccine against Vibrio harveyi, V. alginolyticus and Streptococcus iniae, delivered by intraperitoneal injection in Asian seabass. The fish were divided into three groups with 60 fish in triplicate: I) a control group injected with phosphate-buffered saline (PBS), II) a group vaccinated by polyvalent vaccine (V. alginolyticus + V. harveyi + S. iniae) and III) a group vaccinated with the same polyvalent vaccine plus an oral booster. Immunological parameters and antibody titer were measured before and at three, five-, and eight-weeks post-vaccination. The efficacy of the killed vaccine was assessed five weeks post-vaccination by challenging with each isolate separately. The vaccinated groups had higher survival rate than control group. The highest relative percentage survival rate, 85.71 ± 3.57 % was observed in group III when challenged with V. harveyi. The vaccinated fish produced significantly higher antibody titers against V. alginolyticus, V. harveyi and S. iniae than the control group (P < 0.05). Non-specific immune parameters were significantly enhanced in the vaccinated groups, especially group III, compared to the control. The results demonstrated that the administration of a killed polyvalent vaccine can effectively protect Asian seabass against V. alginolyticus, V. harveyi and S. iniae.

Immune profiling of rainbow trout (Oncorhynchus mykiss) exposed to Lactococcus garvieae: Evidence in asymptomatic versus symptomatic or vaccinated fish

Lactococcosis, caused by the Gram-positive bacterium Lactococcus garvieae, is a major concern in rainbow trout (Oncorhynchus mykiss) farms, which are regularly affected by outbreaks especially during the summer/fall months. In these farms, unvaccinated healthy and symptomatic fish can coexist with vaccinated fish. In the present study, innate (leukogram, serum lysozyme activity, peroxidase activity, antiprotease activity, bactericidal activity, total IgM and total proteins), and specific immune parameters (serum antibodies to L. garvieae) were assessed in unvaccinated adult rainbow trout naturally exposed to the pathogen, with or without evidence of clinical signs, or subjected to vaccination. Blood was drawn from all three groups, and blood smears were prepared. Bacteria were found in the blood smears of 70% of the symptomatic fish but not in any of the asymptomatic fish. Symptomatic fish showed lower blood lymphocytes and higher thrombocytes than asymptomatic fish (p ≤ .05). Serum lysozyme and bactericidal activity did not vary substantially among groups; however, serum antiprotease and peroxidase activity were significantly lower in the unvaccinated symptomatic group than in the unvaccinated and vaccinated asymptomatic groups (p ≤ .05). Serum total proteins and total immunoglobulin (IgM) levels in vaccinated asymptomatic rainbow trout were significantly higher than in unvaccinated asymptomatic and symptomatic groups (p ≤ .05). Similarly, vaccinated asymptomatic fish produced more specific IgM against L. garvieae than unvaccinated asymptomatic and symptomatic fish (p ≤ .05). This preliminary study provides basic knowledge on the immunological relationship occurring between the rainbow trout and L. garvieae, potentially predicting health outcomes. The approach we proposed could facilitate infield diagnostics, and several non-specific immunological markers could serve as reliable indicators of the trout's innate ability to fight infection.

An oral pH-responsive Streptococcus agalactiae vaccine formulation provides protective immunity to pathogen challenge in tilapia: A proof-of-concept study

Intensive tilapia farming has contributed significantly to food security as well as to the emergence of novel pathogens. This includes Streptococcus agalactiae or Group B Streptococcus (GBS) sequence type (ST) 283, which caused the first known outbreak of foodborne GBS illness in humans. An oral, easy-to-administer fish vaccine is needed to reduce losses in fish production and the risk of zoonotic transmission associated with GBS. We conducted a proof-of-concept study to develop an oral vaccine formulation that would only release its vaccine cargo at the site of action, i.e., in the fish gastrointestinal tract, and to evaluate whether it provided protection from experimental challenge with GBS. Formalin-inactivated S. agalactiae ST283, was entrapped within microparticles of Eudragit® E100 polymer using a double-emulsification solvent evaporation method. Exposure to an acidic medium simulating the environment in tilapia stomach showed that the size of the vaccine-loaded microparticles decreased rapidly, reflecting microparticle erosion and release of the vaccine cargo. In vivo studies in tilapia showed that oral administration of vaccine-loaded microparticles to fish provided significant protection from subsequent homologous pathogen challenge with GBS ST283 by immersion compared to the control groups which received blank microparticles or buffer, reducing mortality from 70% to 20%. The high efficacy shows the promise of the vaccine platform developed herein, which might be adapted for other bacterial pathogens and other fish species.

Protection of Teleost Fish against Infectious Diseases through Oral Administration of Vaccines: Update 2021

Immersion and intraperitoneal injection are the two most common methods used for the vaccination of fish. Because both methods require that fish are handled and thereby stressed, oral administration of vaccines as feed supplements is desirable. In addition, in terms of revaccination (boosting) of adult fish held in net pens, oral administration of vaccines is probably the only feasible method to obtain proper protection against diseases over long periods of time. Oral vaccination is considered a suitable method for mass immunization of large and stress-sensitive fish populations. Moreover, oral vaccines may preferably induce mucosal immunity, which is especially important to fish. Experimental oral vaccine formulations include both non-encapsulated and encapsulated antigens, viruses and bacteria. To develop an effective oral vaccine, the desired antigens must be protected against the harsh environments in the stomach and gut so they can remain intact when they reach the lower gut/intestine where they normally are absorbed and transported to immune cells. The most commonly used encapsulation method is the use of alginate microspheres that can effectively deliver vaccines to the intestine without degradation. Other encapsulation methods include chitosan encapsulation, poly D,L-lactide-co-glycolic acid and liposome encapsulation. Only a few commercial oral vaccines are available on the market, including those against infectious pancreatic necrosis virus (IPNV), Spring viremia carp virus (SVCV), infectious salmon anaemia virus (ISAV) and Piscirickettsia salmonis. This review highlights recent developments of oral vaccination in teleost fish.

Expedition of Eudragit® Polymers in the Development of Novel Drug Delivery Systems

Eudragit® polymer has been widely used in film-coating for enhancing the quality of products over other materials (e.g., shellac or sugar). Eudragit® polymers are obtained synthetically from the esters of acrylic and methacrylic acid. For the last few years, they have shown immense potential in the formulations of conventional, pH-triggered, and novel drug delivery systems for incorporating a vast range of therapeutics including proteins, vitamins, hormones, vaccines, and genes. Different grades of Eudragit® have been used for designing and delivery of therapeutics at a specific site via the oral route, for instance, in stomach-specific delivery, intestinal delivery, colon-specific delivery, mucosal delivery. Further, these polymers have also shown their great aptitude in topical and ophthalmic delivery. Moreover, available literature evidences the promises of distinct Eudragit® polymers for efficient targeting of incorporated drugs to the site of interest. This review summarizes some potential researches that are being conducted by eminent scientists utilizing the distinct grades of Eudragit® polymers for efficient delivery of therapeutics at various sites of interest.

High efficacy and economical procedure of oral vaccination against Lactococcus garvieae/Streptococcus iniae in rainbow trout (Oncorhynchus mykiss)

The present study was aimed to examine the efficacy of chitosan-alginate coated vaccines against pathogenicity of Lactococcus garvieae and Streptococcus iniae in rainbow trout. Fish were divided into four groups including: Group A: fish immunized by chitosan-alginate coated vaccine, Group B: fish immunized by non-coated vaccine, Group C: fish feed by chitosan-alginate coated pellets without vaccine and Group D: fish feed by basic diet (non-coated and without vaccine). In groups A and B, the vaccination was carried out for 14 days and after that supplemented with fundamental diet (control diet). Comparable to groups A and B, fish of group C were also fed 14 days with test diets and after that fed control food. On day 0, 20, 40 and 60 of the experiment, serum samples were given. Fish have been challenged with live L. garvieae and S. iniae after 60 days. The levels of bactericidal activity and complement activity among innate immunity components extended on day 20 of the research and after that decreased in group A and B (P < 0.05) all through the examination. The relative expression of IL-6 and IgM in groups A and B extended on examination day 20. The expression of these genes illustrated no advancements in different groups in during the examination (P > 0.05). In group A, the serum antibody titer against L. garvieae and S. iniae broadly raised on day 40 and 60 of examination, whereas in group B, the immune response titer against S. iniae and L. garvieae illustrated a significant elevation on day 60 of the trial (P < 0.05). After challenge with live bacteria, survival rate of 83 ± 9.1%(challenged with S. iniae) and 72.18 ± 9.8% (challenged with L. garvieae) were gotten independently in group A, which were higher than survival of other exploratory groups (P < 0.05). In conclusion, the results of the present examination appear that the orally vaccination of rainbow trout with chitosan-alginate covered vaccine stimulates immunity system and also efficiently protects rainbow trout against Lactococcus garvieae and Streptococcus iniae.

Valuable method for production of oral vaccine by using alginate and chitosan against Lactococcus garvieae/Streptococcus iniae in rainbow trout (Oncorhynchus mykiss)

The effectiveness of ionotropic gelation method (by combining alginate and chitosan) vaccine against Lactococcus garvieae and Streptococcus iniae was examined in rainbow trout. Fish were separated into four groups and fed the distinctive examined feeds. Our groups were included: A) fish immunized by chitosan-alginate coated vaccine, B) fish immunized by non-coated vaccine, C) fish feed by chitosan-alginate coated pellets without vaccine and D) fish feed by basic diet (non-coated and without vaccine). In groups A and B, the vaccination was carried out for 14 days. Fish of group C, like groups A and B were fed 14 days with pellets covered with chitosan-alginate without vaccine and a short time later they were fed with control diet. On day 0, 20, 40 and 60 of the trial, serum samples were extracted. Fish were challenged with L. garvieae and S. iniae after 60 days of research. Innate immunity components containing complement activity, total protein and IgM appeared no significant changes nearly in all groups during the 60 days that the examination finished. Although, bactericidal activity and lysozyme activity demonstrated a significant increase on days 20, 40 and 60 in group A compared to control groups (C and D) (P < 0.05) and similar results about the blood respiratory burst activity just on days 20 and 40 were obtained. Also, the relative expression of IL-6 of group A, was significantly higher compared to all of other groups (B, C and D) on days 20 and 60 of experiment (P < 0.05). The same results were obtained about the relative expression of IgM. The serum ELISA antibody titer against L. garvieae, increased significantly on days 20 and 40 of experiment in fish immunized by chitosan-alginate coated vaccine (Group A) compared to control groups (C and D)(P < 0.05) while the result of ELISA test against S. iniae was significantly higher on days 40 and 60 of experiment in group A compared to groups B, C and D (P < 0.05). After challenge with these two live bacteria (S. iniae and L. garvieae), a survival rates of 76.67 ± 5.77% (challenged with S. iniae) and 66.67 ± 5.77% (challenged with L. garvieae) were seen in group immunized with chitosan-alginate coated vaccine (Group A), which were higher than survival rates gotten in other trial groups (P < 0.05). The consequences of the present experiment show that the oral vaccination of rainbow trout with improved chitosan-alginate (via ionotropic procedure) (group A) properly secures this important fish against Lactococcus garvieae and Streptococcus iniae.