Chilean vaccine cut lice infestation by up to 73% in trials
'IPath' also believed to have boosted efficacy of SRS vaccines by reducing 'immune fatigue'
Published
Recently, scientists from Chile’s Interdisciplinary Centre for Aquaculture Research (Incar2) published new background information on their prototype vaccine for sea lice, “IPath”, a recombinant formulation with chelating properties on metals such as iron. A chelating agent binds a molecule to a metal ion, neutralising the metal and preventing it from reacting with other substances.
In the new study, experts discovered that IPath, both on its own and in combination with two commercial vaccines for Piscirickettsia salmonis, succeeded in reducing the sea lice load and delaying mortality from salmonid rickettsial septicaemia (SRS).
In conversation with Fish Farming Expert's Chilean sister site, Salmonexpert.cl, Dr Antonio Casuso, one of the researchers involved in the development, explained that the basis of this synergy lies in the activation of different but complementary immunological pathways.
“IPath and commercial vaccines activate different mechanisms of the fish’s immune response, which are also complementary. IPath limits the availability of iron, an essential micronutrient for sea lice and P. salmonis, while commercial vaccines activate specific mechanisms against bacterial and viral pathogens,” said Casuso.
According to the researcher, the combination generates a more balanced response at the transcriptomic level, since the fish simultaneously activates iron regulation genes and key immune genes such as cathelicidin, MHC class I and interferon regulatory factor, suggesting a coordinated defence against these pathogens.
Productive impact
One of the most outstanding results of the study was the reduction of up to 73% in the number of Caligus rogercresseyi, the species of lice prevalent in Chile, on farmed salmon.
“A reduction of this magnitude is highly significant because Caligus rogercresseyi is one of the main health costs in Chilean salmon farming. This translates into fewer antiparasitic treatments, cost savings, and less selection pressure for resistance,” said Casuso.
“Furthermore, it reduces chronic stress, improves feed conversion, and lowers mortality in the face of bacterial challenges. In other words, the benefit is not limited to controlling the ectoparasite, but also results in a better overall condition of the fish when faced with coinfection with P. salmonis.”
The study also revealed limitations when using only commercial vaccines. For example, the group immunised only with commercially available vaccines for SRS showed a less effective immune response, with suppression of antimicrobial peptides and activation of stress-associated pathways.
Immune fatigue
“This group showed the highest number of differentially expressed genes, but, paradoxically, a less effective immune response. We interpret this as possible immune fatigue or exhaustion stemming from the previous challenge with sea lice,” said Casuso.
“In contrast, the fish vaccinated with commercial vaccines along with IPath had less stressed immune systems, due to the low infestation pressure from sea lice. This indicates that having a combined strategy for the prevention of sea lice and bacterial pathogens would improve the performance of the fish when exposed to different pathogens during the production cycle.”
Could these types of results explain the gaps sometimes observed between experimental efficacy and field results?
In response to this question, Casuso said: “Yes, we believe this is one of the most plausible explanations for that gap. A vaccine that works very well in the laboratory against a single, controlled pathogen may behave differently in a field setting where multiple stressors coexist.
“This reinforces the need to evaluate vaccines against different target pathogens in coinfection models that are more representative of real-world production. However, it is essential to complement these findings with field trials under actual growing conditions.”
Next steps for a commercial vaccine
Regarding the future of IPath and how far it is from becoming a commercial product, Dr Valentina Valenzuela, also a scientist at Incar2, indicated that the main obstacle is production scalability.
However, they have made progress in implementing new antigen expression platforms, based on Bacillus Spore Surface Display (BSSD) technology, which would allow for lower-cost production scaling, as well as generating oral versions of this vaccine as a booster throughout the production process.
“Furthermore, the transition to commercialisation requires additional steps, such as validation under field conditions and gathering the background information necessary to obtain the permits required by regulations. For this reason, we cannot yet announce a launch date, although we would like it to be one of the milestones of this new phase for Incar2 in the next five years,” concluded Valenzuela.
