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Immunization with bacterial antigens: piscirickettsiosis
P A Smith1, J R Contreras, J J Larenas
1Faculty of Veterinary Sciences, University of Chile, Santiago, Chile.
Developments in Biological Standardization
|January 1, 1997
Summary
Piscirickettsiosis, a serious salmonid fish disease, was studied to assess vaccine efficacy. Formalin-killed bacterins showed immunoprotective responses in coho salmon and rainbow trout, indicating potential for disease control.
Area of Science:
- * Aquatic Animal Health
- * Fish Immunology
- * Bacteriology
Background:
- * Piscirickettsiosis is a significant septicaemic disease in farmed salmonids, caused by *Piscirickettsia salmonis*.
- * First identified in Chile in 1989, it causes high mortality in cultured salmonids and has spread globally.
- * Limited knowledge exists regarding fish immune responses to *P. salmonis*, necessitating standardized challenge models for vaccine efficacy testing.
Purpose of the Study:
- * To determine lethal dose 50% (LD50) and infectivity dose 50% (ID50) for *P. salmonis* in coho salmon and rainbow trout.
- * To evaluate the immunoprotective efficacy of formalin-killed bacterins against piscirickettsiosis in salmonids.
- * To investigate the impact of antigen concentration and booster injections on antibody response.
Main Methods:
- * Determination of LD50 and ID50 using intraperitoneal (i.p.) injections of *P. salmonis* in coho salmon and rainbow trout.
- * Field trials involving i.p. injection of formalin-killed bacterins into coho salmon followed by natural challenge in endemic seawater.
- * Vaccination trials in rainbow trout with varying antigen concentrations and booster injections, followed by i.p. challenge with *P. salmonis*.
- * Measurement of antibody levels using radio-immunoassay (RIA).
Main Results:
- * Intraperitoneal challenge methods were established for coho salmon and rainbow trout.
- * Vaccinated coho salmon groups showed significantly lower cumulative mortality compared to controls in a field trial, indicating immunoprotection.
- * Vaccinated rainbow trout exhibited reduced mortality, though the challenge level was low; antibody levels increased post-vaccination, peaking at day 40.
- * Higher antibody levels were observed in rainbow trout vaccinated with concentrated antigen and receiving booster injections.
Conclusions:
- * Formalin-killed bacterins can induce an immunoprotective response against piscirickettsiosis in salmonids.
- * Standardized challenge models are crucial for evaluating vaccine efficacy.
- * Further research is warranted to optimize vaccine formulations and delivery for effective piscirickettsiosis control.