Mary F. Tatner

The potency of adjuvanted injected vaccines in rainbow trout (Salmo gairdneri Richardson) and bath vaccines in Atlantic salmon (Salmo salar L.) against furunculosis

Abstract The efficacy of adjuvanted vaccine (administered IP) was evaluated in rainbow trout, Salmo gairdneri Richardson. In general, simple mineral oil-based adjuvants resulted in protection against furunculosis, vibriosis and enteric red mouth (ERM). The addition of whole cell bacterin to the adjuvant doubled protection to about 40 relative percentage protection (RPP). Increasing the administration volume also improved protection. The efficacy of bath vaccine was also evaluated in Atlantic salmon, Salmo salar. Booster vaccinations using Aeromonas salmonicida whole cells were effective against furunculosis (48.5 RPP), when given 4 weeks after the primary vaccination. A single vaccination using whole cells extracted with the non-ionic detergent Triton X-100 resulted in protection against furunculosis (29.9 RPP), while bacteria treated with EDTA gave little or no protection. Untreated whole cells gave 9.9 RPP. Extracellular products (ECP) from Aeromonas salmonicida were effective in protection when presented in particularised form, by binding ECP to polystyrene beads (35.6 RPP). Soluble ECP vaccine provided no protection at all.

The quantitative relationship between vaccine dilution, length of immersion time and antigen uptake, using a radiolabelled Aeromonas salmonicida bath in direct immersion experiments with rainbow trout, Salmo gairdneri

Abstract A radiolabelled Aeromonas salmonicida antigen bath was used to quantify uptake after immersion for varying periods of time in bath dilutions of 1 10 , 1 100 or 1 200 . Provided the antigen concentration was not limiting, lengthening the immersion time did not result in greater uptake. However, when the antigen concentration was low, proportionally greater periods of time were needed for antigen uptake to occur. A constant proportion of the total antigen uptake was found in the gut. The variable exerting the largest effect on uptake, however, was fish size, with larger fish sequestering more antigen.

Susceptibility and immunity to Vibrioanguillarum in post-hatching rainbow trout fry, Salmogairdneri richardson 1836

Rainbow trout fry were tested for their susceptibility to experimental infection with Vibrio anguillarum, and their ability to mount an immune response against it, from the age of 2 weeks post-hatch onwards. Bath challenges were ineffective in inducing vibriosis until 6-8 weeks post-hatch, and then only low levels of specific mortality ensued, even at very high doses. However, at the earliest age tested, 7 weeks post-hatch, the fry were susceptible to infection by an intraperitoneal injection with live organisms. Protective immunity was evident in fry vaccinated by direct immersion as early as 2 weeks post-hatch (at an average weight of 0.14g), when tested by intraperitoneal challenge. By the time the fry reached 0.5g (10 weeks after hatching), protection levels had reached 50% for direct immersion vaccination and 100% for intraperitoneal vaccination. An oral vaccination, from first feeding onwards, proved ineffective in inducing immunity. The results are discussed in relation to the onset and maturation of immunological competence in rainbow trout.

The effects of vaccine dilution, length of immersion time, and booster vaccinations on the protection levels induced by direct immersion vaccination of brown trout, Salmo trutta, with Yersinia ruckeri (ERM) vaccine

Abstract Brown trout, Salmo trutta , were vaccinated by direct immersion with Yersinia ruckeri vaccine, using different combinations of vaccine dilution and length of immersion time. On intraperitoneal challenge 5 weeks later, the highest protection level recorded was that achieved by vaccinating with a 1 2000 vaccine solution for 6 h. At very high dilutions of the vaccine, the immersion times needed to be increased by a proportionately much greater amount for effective vaccination to occur. Booster vaccinations were found to result in increased protection levels only when the primary and secondary vaccinations were performed using the vaccine at dilutions of 1 10 and 1 100 . The results are discussed in terms of the effects of dose and administration route on the formation of immunological memory in fish, and the difficulties encountered in defining high and low dose vaccination by direct immersion.

The effects of early exposure to Vibrio anguillarum vaccine on the immune response of the fry of the rainbow trout, Salmo gairdneri Richardson

Abstract No tolerance induction occurred in rainbow trout fry, pre-exposed to Vibrio anguillarum , when vaccinated at various weight classes by direct immersion or intraperitoneal injection. A period of unresponsiveness to the vaccine was detected in the very earliest groups of fry (vaccinated, necessarily, by direct immersion), but, using a radiolabelled vaccine preparation, this was found to be due to a complete lack of antigen uptake at these stages. Once the fry started to respond, they responded quite well and at relatively low water temperatures.

Lymphocyte migration and localisation patterns in rainbow trout Oncorhynchus mykiss, studied using the tracer sample method

The localisation of 3 H-thymidine labelled lymphocytes after intravenous injection was studied in three experimental designs. Firstly, peripheral blood lymphocytes were separated into sIg + and sIg − and injected back into the same fish. After 24 h, and a passage through the thymus, the distribution of sIg + between the spleen and kidney was approximately the same, but more of the sIg − cells localised in the kidney. Secondly, unseparated lymphocytes were injected into non-histocompatible recipients, and studied over time. By 72 h, 42% of the total cells were in the spleen. Thirdly, organ specific lymphocytes were separated into sIg + and sIg − cells and injected into non-histocompatible recipients. It was found that sIg − cells (from the spleen, kidney and thymus) migrated preferentially to the spleen. The conclusion is drawn that the phenomenon of ecotaxis occurs in fish.

FACTORS INFLUENCING THE EFFICACY OF VACCINES AGAINST VIBRIOSIS CAUSED BY VIBRIO ANGUILLARUM

Publisher Summary This chapter discusses some of the factors influencing the efficacy of vaccines against vibriosis caused by vibrio anguillarum. Vaccines against bacterial diseases are playing an increasingly important role in the management of intensively reared fish. From the point of view of minimizing the work and stress involved in vaccinating fish, oral dosing would clearly be the method of choice. Fish vaccinated by intraperitoneal injection produce good antibody responses, but the two non-parenteral routes produce little or no circulating antibody. If the circulating antibody is only part of the protective mechanism against vibriosis, then other aspects of the immune response must be relevant. Both oral administration of vaccine and direct immersion of fish in vaccine are effectively local applications of antigen to mucus membranes, one to the gastrointestinal tract and the other to the skin and gills. There are no reported investigations into the role of locally produced antibody in vibriosis.

Autoaggregation and extracellular A-layer protein in Aeromonas salmonicida

Abstract Fifteen strains of Aeromonas salmonicida were examined for the presence of an extracellular protein A-layer. The presence of an A-layer has been associated with the property of bacterial autoaggregation. However, three of the ten autoaggregating strains examined in this study showed no detectable A-layer subunit protein.

Quantitative and qualitative differences in the antibodies produced by immunosuppressed rainbow trout, Oncorhynchus mykiss, to Aeromonas salmonicida

Abstract The quantitative and qualitative differences in the antibodies produced by rainbow trout, Oncorhynchus mykiss , against Aeromonas salmonicida were studied in fish which had been experimentally immunosuppressed by short-term thymectomy, cortisol or cyclophosphamide injections. At the doses and timings used, the immunosuppressive treatments did not effect antibody production after one or two antigen injections, with the exception of the thymectomy procedure which allowed expression against an ECP antigen after a second antigen exposure.

The effect of thymectomy on the vaccine-induced protection to Yersinia ruckeri in rainbow trout, Salmo gairdneri.

The vaccination of commercial fish stocks against bacterial diseases such as vibriosis, furunculosis and enteric red mouth disease is now commonplace. The vaccines are usually administered by dip/bath or injection, and result in specific and long lasting protection against virulent challenge. However, the mechanism(s) of the immunity induced by vaccination are still unclear. Several studies have reported no correlation between protection and circulating antibody (Michel, 1982) or other parameters such as bacterial effects of serum or mucus and phagocytosis by peritoneal exudate cells (Tatner and Horne, 1986).