Don’t hold your breath waiting on a sea lice vaccine.
Here’s the next installment in my Understanding Fish Farming blog series. This one is written in response to some headlines I saw this week suggesting development of an effective vaccine against sea lice was imminent. It’s a great idea and I’d love to have one but it’s just not imminent.
Everyone, including me, likes the idea of a silver bullet vaccine making an existential problem disappear. The salmon industry could use one when it comes to dealing with mounting problems associated with controlling sea lice and it is important to continue vaccine research efforts to find an eventual solution.
Successful examples
A few examples of truly effective fish vaccines do exist and their role in reducing mortality and antibiotic usage can’t be understated. Three examples come to mind:
Vibrio vaccines in the early days of the industry were transformative and dramatically reduced antibiotic usage
The IHN (infectious hematopoietic necrosis) virus threatened to wipe out the BC salmon farming industry until an effective DNA vaccine was developed (now the @Liberal Party of Canada has taken up the mantle of attempting to wipe out the BC industry)
A more recent example, Clynav, is providing effective relief against the PD (Pancreas Disease) virus in Norway.
When vaccination typically occurs
Vaccines target single-celled organisms like vibrio anguillarum or even simpler organisms like viruses. They are applied at the hatchery in freshwater, under controlled circumstances a few weeks or months before the fish go to sea. At this point in their life cycle, vaccinated fish weight – 50g to 100g. Once vaccinated, salmon are held in freshwater to allow their immune reaction to develop and to allow the wounds, from being vaccinated and handled, to heal.
The impacts of being vaccinated
Vaccination is a traumatic experience for any animal – it hurts, creates a wound site and often has residual effects that can take days to pass. To some extent, it’s worse for salmon, their immune systems are primitive (in my non-veterinary opinion) and rely on their skin and mucous layers. During vaccination, the process of being crowded can result in scale-loss and disruption of the mucous layer and, of course, the injection of a vaccine creates a wound and potential pathway for infection by other organisms. Perhaps more importantly, salmon are not charismatic animals like swine, cattle or people. They do not develop relationships with their handlers and every single handling event will cause damage and mortality.
Vaccines for multi-cellular organisms
Truly effective vaccines against multi-cellular organisms that offer long-term protection don’t exist. Maybe they will in the future, but realistically, they are many years away. Reflect for a moment on the tremendous efforts that went into developing covid virus vaccines, a much simpler organism than a sea louse. The malaria parasite causes incredible human suffering and, yet, while some vaccines can be part of an effective control strategy, there are no silver bullets resulting from enormous efforts in looking for one. Yet.
Oral and immersion vaccines
Once again, I’ll caveat this statement by clarifying that I am not a veterinarian, but having managed salmon farms for more then 20 years, I will stand by the statement that while oral and immersion vaccines are a great idea and have some benefits as part of an overall health management program, none have proven capable of stimulating an extended protection against viral, bacterial or parasitic infections. This is an important area of research but, realistically, not something that should be considered around the corner.
Parasiticides are not vaccines
There are some good examples of oral and immersion parasiticides being used to control sea lice, but they are not vaccines. Vaccines stimulate the immune system of the host, while parasiticides rely on introduction of a pharmaceutical ingredient to disrupt the life cycle of the targeted parasite. I can’t comment on it yet, but I am aware of one parasiticide that promises to offer tremendous relief to salmon and salmon farmers globally. There is relief on the horizon, just not a vaccine.
Boosters
There have been vaccines developed for ticks in cattle. Ticks are non-scientifically like sea lice – they are complex, multi life stage parasitic organisms. In the case of cattle vaccines against ticks, none are 100% effective against preventing infestations and require injected boosters every few months. In the case of an Australian tick vaccine, uptake of a vaccine was limited as the impacts of having to collect and immunize each cow was deemed worse than the impact of the tick.
For salmon, a vaccine that requires an injected booster might just be worse than the infection. The process of crowding, pumping, de-watering and injecting each individual salmon on a farm will kill a significant percentage of the animals and once the injection process is complete, the salmon will be returned to the pens with an open wound, missing scales and a disturbed mucous layer – ripe for infection. We’ve seen this situation play out as industry has had to rely on mechanical delousing systems. The result has been a steady deterioration of fish health results.
Conclusion
A sea lice vaccine would be a fantastic breakthrough, but it’s not just around the corner. The salmon industry must continue using integrated pest management strategies and push for research breakthroughs.
If you are still reading, thank you. Feedback welcomed.
Alan