Hi Bikrmajit:

Your experimental design sounds about right. The develop immunity for a vaccine usually takes 8 weeks or 650 accumulated thermal units (ATU), when a pathogen challenge should be conducted. Usually oral vaccines are given for a shortish period (10 days) and then you have to wait for immunity development (650 ATUs). If you plan to prove that immunity is longer than 650 ATUs, then you usually need to perform and additional challenge at 100 or 200ATUs. You can check immunity through several methods such as Ig measurements, citokines, etc. I do not quite understand what you mean by "avoiding oral tolerance to the antigen". In general terms, the development of protection is dependent on the life stage of the salmon and environmental variables. For example, a minimum weight of 10-30 g must be obtained before any immunization, due to the fact that fish immune system is better developed at that weight. Also, water temperature is important. I have seen experiments running at 13 or 15ºC, just to speed things up. This situation is both highly unreal in production systems and harmful in terms of fish welfare. What you should try to achieve is something that is "real" in terms of applicability (ie: use normal range of temperature, size of fish, cohabitation challenges, etc).

Hope this information helps you and good luck with your research

Best

H

Thanks for your suggestions Hernan. We're trying to maintain a realistic set of environmental parameters, if nothing else then to keep the results more applicable to industry.

With respect to my specific question, oral tolerance - or oral conditioning against response to an antigenic substance - can be achieved through sustained continuous exposure to the antigenic substance. This can be useful in certain cases, but of course, since our objective is to elicit a response, we want to try and avoid that situation occurring. We were thinking of an interrupted/intermittent antigen feeding schedule over the 8 weeks, possibly as an initial and booster, or even more evenly spread out. That is what I was particularly hoping to get some suggestions on.

Thanks again for your suggestions.

Perfect. Current vaccination in Chile are for example, 10 days oral administration through feed, and thats it. I would suggest short period of feeding with high antigen dose plus a good adjuvant (for example Quillaja saponin). We have done some work on this and using saponin can potentially increase the immune response (membrane permeabilization, increase microvilli area, increase in macrophage and citokine production). You can also "prime" the fish with one dose and then repeat it once 2 weeks later (150ATUs).

Cheers

H

Thanks Hernan - That's just the sort of thing I was looking for!

Cheers