Commercial vaccines do not confer protection against two genetic strains ofPiscirickettsia salmonis, LF-89-like and EM-90-like, in Atlantic salmon

Abstract

In Atlantic salmon, vaccines have failed to control and prevent Piscirickettsiosis, for reasons that remain elusive. In this study, we report the efficacy of a commercial vaccine developed with the Piscirickettsia salmonis isolate AL100005 against other two isolates which are considered highly and ubiquitously prevalent in Chile: LF-89-like and EM-90-like. Two cohabitation trials were performed to mimic real-life conditions and vaccine performance: 1) post smolt fish were challenged with a single infection of LF-89-like, 2) adults were coinfected with EM-90-like and a low coinfection of sea lice. In the first trial, the vaccine delayed smolt mortalities by two days; however, unvaccinated and vaccinated fish did not show significant differences in survival (unvaccinated: 60.3%, vaccinated: 56.7%; p = 0.28). In the second trial, mortality started three days later for vaccinated fish than unvaccinated fish. However, unvaccinated and vaccinated fish did not show significant differences in survival (unvaccinated: 64.6%, vaccinated: 60.2%, p= 0.58). Thus, we found no evidence that the evaluated vaccines confer effective protection against of LF-89-like or EM-90-like with estimated relative survival proportions (RPSs) of −9% and −12%, respectively. More studies are necessary to evaluate whether pathogen heterogeneity is a key determinant of the vaccine efficacy against P. salmonis.

Why vaccines fail against Piscirickettsiosis in farmed salmon and trout and how to avoid it: A review

“…Thus ( 72 ), suggested that this strong local response could lead to an overestimation of vaccine efficacy if fish are IP-challenged a few weeks after vaccination. These results are consistent and explain very well the low efficacy of some experimental and commercial vaccines observed in cohabitation trials despite achieving high amounts of host IGM expression ( 61 , 110 – 113 ).…”