Elsevier

Fish & Shellfish Immunology

Volume 88, May 2019, Pages 293-300
Fish & Shellfish Immunology

Full length article
Efficacy of Injectable and Immersion Polyvalent Vaccine against Streptococcal Infections in Broodstock and Offspring of Nile tilapia (Oreochromis niloticus)

https://doi.org/10.1016/j.fsi.2019.02.042Get rights and content

Highlights

  • ME-VAC Aqua Strept is a polyvalent inactivated vaccine against Streptococcal infections in Nile tilapia.

  • Nano particulate adjuvants improve the efficacy of mucosal vaccines and prolong their immune response.

  • Vaccination of tilapia offspring by immersion provided long period of protection up to three months.

  • Parental vaccination of broodstock improves the seed quality, quantity and survivability.

Abstract

A vaccine against streptococcosis, lactococcosis and enterococcosis in tilapia was formulated, ME-VAC Aqua Strept, as a polyvalent inactivated vaccine containing Streptococcus agalactiae, S. iniae, Lactococcus garvieae and Enterococcus faecalis along with a nano-particulate adjuvant. Use of ME-VAC Aqua Strept by injection or immersion resulted in an improved non-specific and adaptive immunity of broodstock and offspring. Intra-peritoneal vaccination of tilapia broodstock increased the total leukocyte count, phagocytosis, lysozyme activity, antibody titer, number of seeds/vaccinated broodstock, seeds quality and survival rates. Also, immersion mass vaccination of tilapia larvae provided a long period of protection up to three months, with a relative percent of survivability (RPS) not less than 60% at this time. To our knowledge, this vaccine may be the first to offer a combined protection against streptococcosis, lactococcosis and enterococcosis in tilapia. The results support the use of this vaccine as an effective tool for disease control and well-being of fish.

Introduction

In September 2015, the world leaders agreed to implement the so-called sustainable development Agenda, which mainly vows to eradicate hunger by 2030 via innovative agricultural projects [1,2]. In line with this, intensive farming of Nile tilapia (Oreochromis niloticus); as the first popularly cultured fish in Egypt was started under health surveillance systems and control programs, including vaccines [3,4].

Streptococcosis, Lactococcosis and Enterococcosis are the most frequent diseases affecting Tilapia production in Egypt [5,6]. These infections are respectively caused by S. agalactiae,S. iniae, L. garvieae, and E. faecalis particularly during summer [5,6]. They may affect fish at all culturing stages [7] and are commonly associated with non-specific lesions, including hemorrhages, exophthalmia, congestion and ocular opacity, melanosis, nervous swimming behavior and rapid mortality, leading to high economic losses in marketable fish size and possible farm closure [5,8].

In Egypt, use of vaccines in fish farms has been hampered by many challenges, including the lack of vaccination programs, high cost of imported vaccines, small value of available tilapia farms, narrow spectrum of cross protection, high mortalities associated with stress during fish handling, cost of anesthetics and the need for trained manpower and equipment. However, the current trend of high scale tilapia production in many farms in Egypt supports the development of effective vaccines to control these circulating diseases.

Most previous research on fish vaccines against streptococcosis was focused on the production of monovalent vaccines that were administered parenterally (I/P) and consisted of formalin killed whole cultures of homologous bacterins against the above pathogens, with or without the extracellular products (ECP). These vaccines showed relative percent survival values (RPS) between 56 and 95% when challenged at 21 or 7 days post-vaccination, respectively [[9], [10], [11]]. Some vaccines contained mineral oil adjuvants to induce higher and longer protection, while others had non-oil adjuvants (e.g., Aquamun) and yielded good protection in rainbow trout, with RPS value up to 83.3% [11]. Limited research was done on polyvalent vaccines.

Three vaccine delivery systems have been used in fish with variable success, depending on the nature of each vaccine and production stage of fish; injection, immersion (dip or bath) and oral [12]. In general, vaccination of broodstock conferred protection of offspring against infection [9]. Tilapia offspring (approximately below 0.5 gm or less than 21 days age) rely on the delivered maternal immune response (innate and adaptive immunity) [9]. While parenteral vaccine delivery has been adopted for larger fish, a more feasible, practical and less hazardous vaccination strategy is highly required especially in fries, fingerlings and in grow out stages.

Recently, a nano-particulate delivery system (O/W adjuvant) has been optimized for mucosal immunity [13] and was found to improve the adsorption of antigens through gill tissues, skin and intestines, promoting their entrapment and retention in the lymphoid tissues. It also provided a slow continuous release of antigens, following the depot effect theory [14]. Soltani et al. [15] and Hwang et al. [16] recorded high protection levels in rainbow trout against Yersinia ruckeri when Montanide IMS 1312 VG was used with the antigen as an immersion adjuvant and similar protection was obtained in Olive flounder (Paralichthys olivaceus) when the same adjuvant was employed in an immersion vaccine against viral hemorrhagic septicemia. Such adjuvant was also reported to protect the antigens from hydrolytic enzymes and low pH of the gut and intestinal mucosal surfaces.

The present study was designed to develop and evaluate a locally prepared vaccine that protects tilapia broodstock and offspring against common infections in tilapia; streptococcal disease, lactococcosis and enterococcosis. The development of high quality bacterial vaccine seeds was the first approach to support the production of a multivalent tilapia vaccine at MEVAC laboratories. The vaccine, ME-VAC Aqua strept, was formulated as a polyvalent inactivated micro-emulsion containing antigens of Streptococcus spp. (S. agalactiae and S. iniae), L. garvieae, and E. faecalis along with Montanide IMS 1312 VG as a nano-adjuvant (Seppic, France). Efficacy and potency of the vaccine were evaluated in both broodstock and fries with a special emphasis on the number of seed/broodstock and mortality percent among tilapia fries at the end of the nursery period.

Section snippets

Phenotypic and molecular characterization

Virulent strains of S. agalactiae, S. iniae, L. garvieae and E. faecalis were isolated from Nile tilapia during disease outbreaks [5,6]. They were cultured on MacConkey-Agar and Trypticase Soy Agar (TSA, Himedia, India), with or without 5% sheep blood. The obtained colonies were examined by Gram staining, colonial morphology on different growth media and hemolytic patterns on blood agar were determined. The phenotypic and molecular characterization attributes were determined prior to using them

Phenotypic and molecular identification

Although S. agalactiae is known to belong to Lancefield group B streptococci as a β-hemolytic microorganism, it may be worth noting to report that all of our isolates recovered from fish were γ-hemolytic. L. garvaiae and S. iniae were α-β hemolytic. E. faecalis was γ-haemolytic. All isolates did not grow on Mac-Conky's agar except Enterococcus faecalis. All bacteria appeared on TSA as pin point to small size, translucent to white colonies and showed Gram positive cocci arranged in pairs or

Discussion

Although huge investments are poured into the Egyptian aquaculture industry, there is a general demand of professional health management to account for disease outbreaks that cause high fish mortalities and economic losses. Streptococcosis, lactococcosis and enterococcosis are among the most common bacterial diseases affecting Nile tilapia and many other fish species, including Asian seabass (Lates calcarifer), grouper (Epinephelus lanceolatus), Japanese flounder (Paralichthys olivaceus),

Acknowledgement

Authors are very grateful to Engineer Ahmed Elsharaky the owner of fish farm and his assistant Mis Aya Hisham for their kind support to achieve our work and their continues follow up of the experiment.

References (38)

  • I. Mulero et al.

    Maternal transfer of immunity and ontogeny of autologous immunocompetence of fish: a minireview

    Aquaculture

    (2007)
  • William Colglazier

    Sustainable development agenda: 2030

    Science

    (2015)
  • M. Kobayashi et al.

    Fish to 2030: the role and opportunity for aquaculture

    Aquacult. Econ. Manag.

    (2015)
  • M. Dadar et al.

    Advances in aquaculture vaccines against fish pathogens: global status and current trends

    Rev. Fish. Sci. Aquacult.

    (2017)
  • Santiago Benites De Pádua et al.

    Health challenges in tilapia culture in Brazil

  • K.M. Osman et al.

    Characterization and susceptibility of streptococci and enterococci isolated from Nile tilapia (Oreochromis niloticus) showing septicaemia in aquaculture and wild sites in Egypt

    BMC Vet. Res.

    (2017)
  • N.M. Abu‐Elala et al.

    Eutrophication, ammonia intoxication, and infectious diseases: interdisciplinary factors of mass mortalities in cultured Nile tilapia

    J. Aquat. Anim. Health

    (2016)
  • S. Jantrakajorn et al.

    Comprehensive investigation of streptococcosis outbreaks in cultured Nile tilapia, Oreochromis niloticus, and red tilapia, Oreochromis sp., of Thailand

    J. World Aquacult. Soc.

    (2014)
  • K.D. Lafferty et al.

    Infectious diseases affect marine fisheries and aquaculture economics

    Annu. Rev. Mar. Sci.

    (2015)
  • Cited by (0)

    View full text