Policy – July 15, 2026
Study: experimental vaccine cuts sea lice by up to 74% in Chilean salmon trial
An experimental recombinant vaccine developed by researchers in Chile reduced sea lice infestations in Atlantic salmon by up to 73.7% and enhanced immune responses when used alongside commercial vaccines against salmon rickettsial syndrome (SRS), according to a peer-reviewed study.
The findings, published in the journal Marine Biotechnology, evaluated the prototype vaccine, IPath, both on its own and in combination with the commercially used BlueGuard and Alpha Ject LiVac SRS vaccines.
Researchers challenged vaccinated salmon with the sea louse Caligus rogercresseyi before infecting the fish with Piscirickettsia salmonis, the bacterium responsible for SRS. Fish receiving IPath alone recorded a 73.7% reduction in sea lice burden, while those receiving the combination of commercial vaccines and IPath achieved a 69.8% reduction.
The study also found that salmon vaccinated with IPath experienced delayed mortality following P. salmonis infection compared with the other treatment groups.
Transcriptome analysis showed that fish receiving the combined vaccination activated genes associated with both innate and adaptive immunity, including cathelicidin, major histocompatibility complex class I and interferon regulatory factor. The researchers also identified increased regulation of genes involved in iron metabolism, supporting the vaccine's proposed mechanism of limiting iron availability to both parasites and bacteria.
By contrast, fish vaccinated only with the commercial SRS vaccines showed suppression of several immune-related genes during co-infection and greater activation of stress-response pathways.
The authors said the results suggest IPath could complement existing vaccination programmes by providing integrated protection against two of the Chilean salmon industry's most significant biological challenges, although further field validation and regulatory approval will be required before any commercial launch.
