Effectiveness of a proteoliposome-based vaccine against salmonid rickettsial septicaemia in Oncorhynchus mykiss

Mario Caruffo,Daniela Siel,Oliver Pérez,Sonia Vidal,Leonardo Sáenz,Paula R Huenchullan,Leonardo Santis

doi:10.1186/s13567-021-00982-2

Abstract

Salmonid rickettsial septicaemia (SRS) is a contagious disease caused by Piscirickettsia salmonis, an intracellular bacterium. SRS causes an estimated economic loss of $700 million USD to the Chilean industry annually. Vaccination and antibiotic therapy are the primary prophylactic and control measures used against SRS. Unfortunately, commercially available SRS vaccines have not been shown to have a significant effect on reducing mortality. Most vaccines contain whole inactivated bacteria which results in decreased efficacy due to the limited ability of the vaccine to evoke a cellular mediated immune response that can eliminate the pathogen or infected cells. In addition, SRS vaccine efficacy has been evaluated primarily with Salmo salar (Atlantic salmon). Vaccine studies using Oncorhynchus mykiss (rainbow trout) are scarce, despite SRS being the leading cause of infectious death for this species. In this study, we evaluate an injectable vaccine based on P. salmonis proteoliposome; describing the vaccine security profile, capacity to induce specific anti-P. salmonis IgM and gene expression of immune markers related to T CD8 cell-mediated immunity. Efficacy was determined by experimental challenge with P. salmonis intraperitoneally. Our findings indicate that a P. salmonis proteoliposome-based vaccine is able to protect O. mykiss against challenge with a P. salmonis Chilean isolate and causes a specific antibody response. The transcriptional profile suggests that the vaccine is capable of inducing cellular immunity. This study provides new insights into O. mykiss protection and the immune response induced by a P. salmonis proteoliposome-based vaccine.

Highlights

The aquaculture industry is threatened by infectious diseases that cause severe economic losses due to low productivity
The average diameter of P. salmonis proteoliposomes was shown by dynamic light scattering to be 250.9 ± 13.2 nm (n = 10) with a low polydispersity index (PDI) of 0.1349 ± 0.03; indicating the degree of dispersion of sizes
Minimal adverse effects were registered in vaccinated fish during the necropsy and none of the vaccinated groups showed more than 2 points in Speilberg Index (0–6); no statistically significant differences were observed between treatments and control (p ≥ 0.05; Kruskal–Wallis, Dunn’s multiple comparison) (Figure 2B)

Summary

Introduction

The aquaculture industry is threatened by infectious diseases that cause severe economic losses due to low productivity. Antibiotics have been used extensively leading to Chilean salmon farming having one of the highest rates of antibiotic consumption per ton of harvested fish in the world [9]; generating an economic and environmental problem. The use of vaccination to prevent disease is used routinely in finfish aquaculture, especially in salmonids [11]. Despite the large number of available vaccines, SRS continues to be the main cause of infectious death by salmonids in Chile

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