Fish Vaccination: A Health Management Tool for Aquaculture
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Fish Vaccination: A Health Management Tool for Aquaculture

Fish Vaccination: A Health Management Tool for Aquaculture

Arun Sudhagar S1, Ferose Khan2 and Linga Prabu D2

1&2PG Scholars

1Department of Fish Pathology & Microbiology

2Division of Fish Nutrition, Biochemistry & Physiology

Central Institute of Fisheries Education

Mumbai-400061, India

Email: arunsaqua@gmail.com, lin17687@gmail.com

Introduction

                 Aquaculture has been globally recognized as the fastest growing food production sector (FAO). The intensive farming of finfishes and shellfishes has led to an imbalance of optimal culture conditions, which shows increased susceptibility to infectious disease. Increased incidence of microbial diseases in aquaculture system is the major obstacle in the success of the industry. Use of antibiotics has attracted lot of criticism due to the issues like antibiotic residues, bacterial drug resistance and toxicity. In this present scenario, vaccination would be the best alternative to combat bacterial and viral disease for the sustainable aquaculture. The first report on fish vaccination was by David C. B. Duff and he is regarded as "Father of fish vaccination".

Concept of vaccination

"Prevention is better than cure"

            Vaccination is an easy, effective and preventive method of protecting fish from diseases. Vaccination is a process by which a protective immune response is induced in an animal by administration of vaccines. Vaccines are preparations of antigens derived from pathogenic organisms, rendered non-pathogenic by various means, which will stimulate immune system of the animal to increase the resistance to the disease on natural encountered with pathogens. Once stimulated by a vaccine, the antibody-producing cells, called B lymphocytes, remain sensitized and ready to respond to the agent should it ever gain entry to the body.

Importance of vaccination

      Vaccines are not the same as antibiotics and generally will not be effective for stopping a disease outbreak once it has begun.

       Vaccines are used to prevent a specific disease outbreak from occurring and are not a therapy.

      Its efficiency exists for a longer duration with one or more treatments.

      No toxic side effects and healthy fish have better growth performance.

      No accumulation of toxic residues

      Pathogen will not develop resistance.

      Theoretically it can control any bacterial and viral disease.

      No environmental impact.

Characteristics of vaccine

     The vaccine used should be safe and should not cause toxicity to the animal.

     The vaccine should have high immunogenicity.

     The vaccine should protect the animal for a longer period. In fish, duration of one year or life long protection can be said to be commercially effective for a vaccine preparation.

     The vaccine should be specific against a particular pathogen. It should not protect or favour the other pathogens.

                                          

Types of vaccines

Killed vaccine

          Vaccines containing killed micro-organisms, these are previously virulent micro-organisms which have been killed with chemicals or heat.

Inactivated vaccine

         An Inactivated Vaccine is culture of an infection agent on a medium and then deactivated using heat or formaldehyde. Viruses are metabolically inert and they cannot be killed.

Attenuated vaccine

         Some vaccines contain live, attenuated virus micro-organisms. These are live micro-organisms that have been cultivated under conditions that disable their virulent properties, or which use closely-related but less dangerous organisms to produce a broad immune response. They typically provoke more durable immunological responses and are the preferred type for healthy adults

Toxoid vaccine

           Toxoids are inactivated toxic compounds in cases where these (rather than the micro-organism itself) cause illness.

Subunit vaccine

            Rather than introducing an inactivated or attenuated micro-organism to an immune system (which would constitute a "whole-agent" vaccine), a fragment of it can create an immune response.

Conjugate vaccine                               

            Certain bacteria have polysaccharide outer coats that are poorly immunogenic. By linking these outer coats to proteins (e.g. toxins), the immune system can be led to recognize the polysaccharide as if it was a protein antigen.

Experimental vaccines

A number of innovative vaccines are also in development and in use:

  • Recombinant Vector - by combining the physiology of one micro-organism and the DNA of the other, immunity can be created against diseases that have complex infection processes
  • DNA vaccination - in recent years a new type of vaccine called DNA vaccination, created from an infectious agent's DNA, has been developed. It works by insertion (and expression, triggering immune system recognition) of viral or bacterial DNA into animal cells. Some cells of the immune system that recognize the proteins expressed will mount an attack against these proteins and cells expressing them. Because these cells live for a very long time, if the pathogen that normally expresses these proteins is encountered at a later time, they will be attacked instantly by the immune system. One advantage of DNA vaccines is that they are very easy to produce and store. DNA vaccination is still experimental.
  • T-cell receptor peptide vaccines are under development for several diseases .These peptides have been shown to modulate cytokine production and improve cell mediated immunity.
  • Targeting of identified bacterial proteins that are involved in complement inhibition would neutralize the key bacterial virulence mechanism.
  • While most vaccines are created using inactivated or attenuated compounds from micro-organisms, synthetic vaccines are composed mainly or wholly of synthetic peptides, carbohydrates or antigens.

Valence

            Vaccines may be monovalent (also called univalent) or multivalent (also called polyvalent). A monovalent vaccine is designed to immunize against a single antigen or single microorganism. A multivalent or polyvalent vaccine is designed to immunize against two or more strains of the same microorganism, or against two or more microorganisms. In certain cases a monovalent vaccine may be preferable for rapidly developing a strong immune.

Adjuvants

Adjuvants are pharmacological or immunological agents capable of modifying the effect of other agents, such as drugs or vaccines. Adjuvants are virtually useless if given alone, but can serve to make a vaccine much more effective. When given together with a vaccine, the adjuvant will stimulate the immune system and increase its response to the vaccine. Exactly how adjuvants work remains unknown. Aluminium salt, virosomes and certain oils are all commonly used as adjuvants for vaccines.

Vaccine delivery system

                There are three methods of vaccination in fish.

1.    Injection delivery system.

2.    Immersion delivery system.

3.    Oral delivery system.

 

Injection delivery system

Injection delivery system is an effective way of inducing antibody response in fish. The injection may be intraperitoneal or intramuscular. But the major setbacks are, it is time consuming, labour intensive and consequently expensive to administer to large number of animals. During the course of injection, handling stress affects their ability to produce optimal immune response. For safe handling and injection, the fish should be of reasonable size. Fry cannot be vaccinated by means of injection. Because of these limitations injection delivery system of vaccines are used in fishes of high unit value to absorb the cost of procedure.

Immersion delivery system

Immersion delivery system of vaccines is a potential commercial process. It is a hyperosmotic immersion technique, where prior to immersion in antigen solution fish are dipped for a short time in a hyperosmotic salt solution which enhances the uptake of antigen. The advantages are, large number of fish can be vaccinated at the same time and it can be used to vaccinate fry of any size above the critical size of immune responsiveness. The main disadvantage of this method is the fish is subjected to stress. Spray vaccination is a variant of direct immersion where antigen in sprayed under pressure on to the fish, as they are propelled along a shallow channel.

Oral delivery system

Oral delivery system through feed is a potentially useful method of vaccination. Besides its simplicity, it is a method of choice for eliciting immune response to enteric pathogens. This method do not cause stress to the fish. It can be used to vaccinate the fish of any size and requires no extra time or labour than normal farm husbandry. The main limitations of this method are, to obtain effective immunity it is necessary to give a large dose of antigen (i.e.) the total amount of antigen needed is much more higher than injection and immersion delivery systems and the immunity which the oral delivery system provokes is poor and not as long lasting as injection delivery system. The poor response is due to poor antigen delivery to immune responsive sites. Due to low pH and high enzymatic activity the vaccine is destroyed in the foregut and causes poor antigen delivery to hind gut and other lymphoid organs of fish. To overcome this problem encapsulated vaccines can be used. Recently biofilm of bacterial pathogen has been evaluated successfully for oral vaccination of fish with high antibody tire and protection. The glycocalyx of biofilm helps to resist the vaccine destruction in the foregut favouring better antigen delivery to immune responsive sites in the hind gut.

 How to achieve optimal effects of vaccines

Using efficient vaccines and administering them correctly is not the only factors affecting the effects of vaccines. Optimal efficiency of vaccines can be achieved by proper fish management practices. Optimal conditions and adequate nutrition are very important and one must also strive to expose the fish to as little stress as possible. The efficiency of a vaccine largely depends on the condition of the immune system and exposing fish to factors that might harm their immune system are therefore highly unadvisable.

List of fish vaccines developed

VACCINES

SPECIES

DISEASE

Aeromonas salmonicida Bacterin

Atlantic salmon

Furunculosis

Vibrio anguillarum-Ordalii-Yersinia ruckeri Bacterin

Rainbow trout

Vibriosis, yersiniosis (enteric red- mouth disease)

Yersinia ruckeri Bacterin

Salmonids

Yersiniosis (enteric red-mouth disease)

Vibrio salmonicida Bacterin

Salmonids

Vibriosis

Vibrio anguillarum-salmonicida Bacterin

Salmonids

Vibriosis

Aeromonas salmonicida Bacterin

Salmonids

Furunculosis

Edwardsiella ictaluri Bacterin

Catfish

Enteric  septicaemia

Spring viraemia of carp virus

Common carp

Spring  viraemia of carp

Koi herpes virus (KHV)

Koi carp

Koi herpes virus (KHV) disease

Biofilm and free-cell vaccines of Aeromonas hydrophila

Indian major carps

Dropsy

Streptococcus agalactiae (group B) vaccine

Tilapia

 

Streptococcosis

Betanodavirus

 

Grouper

Betanodavirus disease

Recent development in fish vaccinology

During the last two decades vaccination has become established as an important method for prevention of infectious diseases in farmed fish, mainly salmonid species. So far, most commercial vaccines have been inactivated vaccines administered by injection or immersion. Bacterial infections caused by Gram-negative bacteria such as Vibrio sp., Aeromonas sp., and Yersinia sp. have been effectively controlled by vaccination. With furunculosis, the success is attributed to the use of injectable vaccines containing adjuvants. Vaccines against virus infections, including infectious pancreatic necrosis, have also been used in commercial fish farming. Vaccines against several other bacterial and viral infections have been studied and found to be technically feasible. The overall positive effect of vaccination in farmed fish is reduced mortality. However, for the future of the fish farming industry it is also important that vaccination contributes to a sustainable biological production with negligible consumption of antibiotics.

Conclusion

            In addition to optimizing husbandry and general management practices, use of vaccines is still limited, is becoming more widespread in certain sectors of aquaculture for disease prevention. A number of vaccines have been in use by the salmonid industry for decades. However, commercial vaccine development for other aquaculture sectors, including producers of warm water fish, is still quite limited. Greater demand by producers and increased levels of research and interest by manufacturers is helping to make vaccination a more viable option. Currently, vaccines are available for some economically important bacterial and viral diseases. Vaccines for protection against parasitic and fungal diseases have not yet been developed.  Vaccination should be considered part of a comprehensive fish health management scheme, and not the only solution for a disease problem.

References

       Biering E., S. Villoing, I. Sommerset, and K.E. Christie. 2005. Update on viral vaccines for fish. Progress in Fish Vaccinology. Developments in Biologicals, P.J. Midtlyng, (ed.): 121:97-113.

       Grisez, L., and Z. Tan. 2005. Vaccine development for Asian aquaculture. In Diseases in Asian Aquaculture, P. Walker, R. Lester, and M.G. Bondad-Reantaso (eds), V: 483-494. Fish Health Section, Asian Fisheries Society, Manila.

       Hastein, T., R. Gudding, and O. Evensen. 2005. Bacterial vaccines for fishan update of the current situation worldwide. Progress in Fish Vaccinology. Developments in Biologicals, P. J. Midtlyng, (ed), 121:55-74.

       Komar, C., W.J. Enright, L. Grisez, and Z. Tan. 2004. Understanding fish vaccination. AQUA Culture AsiaPacific Magazine, pp. 27-29.

       Sommerset, I., B. Krossoy, E. Biering, and P. Frost. 2005. Vaccines for fish in aquaculture. Expert Review of Vaccines 4(1):89-101.

       Gudding, R., Lillehaug, A., Midtlyng, P.J., Brown, F. (Eds.), 1997. Fish Vaccinology. Developments in Biological Standardization, vol. 91. S. Karger, Basel, p. 484.

       Hill, B., 2005. The need for effective disease control in international aquaculture. In: Midtlyng, P.J. (Ed.), Progress in Fish Vaccinology. Developments in Biologicals, vol. 121, pp. 312.


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