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When do we stop sending pyrethroid treated LLITNs into areas where there is pyrethroid resistance?
There is a lot of ongoing debate on how to manage the spectre of pyrethroid resistance and how we provide guidance to country programs on the use of IRS and nets in particular. IRS has come under the microscope in terms of asking the question, 'should we ban pyrethroids for IRS?', however I believe for a reasonable and balanced debate we should also discuss what we do in terms of current LLITN distribution strategy.
Do we really keep sending a long lasting monotherapy (arguably the worst combination for resistance promotion) into areas with emerging or pre-existing pyrethroid resistance? Would an untreated net be a more cost effective strategy in certain West African locations where we are already seeing reports of blood fed mosquitoes inside LLITNs?
This is an important forum topic - thanks Mark, for bringing this up.
I guess that if you would take the extreme view that distributing pyrethroid-treated LLINs in countries where resistance has been found should be stopped, that this would result in a crash of the net market. You would not be able to go almost anywhere in W Africa with LLINs.
There is a technical issue here relating to the excito-repellent effect of nets, and at least one report from Ivory Coast, where physiological resistance was present, but the nets were still keeping mosquitoes at bay (this is similar to the argument that Don Roberts maintains for DDT. Even with resistance, DDT still works). So that's one - is resistance the issue, or the effectiveness in terms of controlling disease transmission. WHO maintains that resistance is more important, others the overall efficacy in terms of controlling malaria.
If you would want to let go of monotherapy, then new classes of insecticides will have to be used on nets (or nets combining more classes). But as you know, good alternatives are lacking for net treatment.
Moreover, having nets treated with specific insecticides that still work distributed to specific countries or even regions therein, is a highly complex issue, both from a manufacturers and distributors point of view.
Imagine UNICEF placing an order for nets whereby they need x amount with permethrin for region y in country z, x amount with deltamethrin for region y1 in country z1, etc.
This is likely to falter. Emphasis should therefore be placed on alternatives, be it new insecticides or other methods (biologicals).
Location
The topic of pyrethroid resistance is very interesting and fortunately the debate is lively and is taking place across many forum.
In regards to use of the AI in IRS vs LLIN's, I think there are two good reasons for preparing for a restriction on the use of it in IRS.
First, IRS is not as sex selective as LLINs, will to a larger degree target females and as well as males and therefore more likely to promote resistance.
Second, from a product development point of view it is much less difficult to use a different AI in an IRS product than it is in an LLIN. If we have a choice to choose a route with less risk of resistance development, we should choose to go that way. For that reason I am enthusiastic about the IRS product submitted for review by Syngenta.
Looking at what is currently under review I find the durable wall lining, a product that will put pyrethroids on the wall for 4yrs particularly depressing.
In regards to whether or not the current level of pyrethroid resistance is detrimental at any significantly level to the operational efficacy of LLIN's, I would say this is questionable. We should definitely monitor for resistance so we prescribe the proper tools for specific situations.
I havent seen reports on LLIN's alone having caused pyrethroid resistance. As far as I understand, resistance is found in areas where pyrethroid use in agriculture is prevalent. Of course, I would accept otherwise if such reports exist.
The last question is somewhat hard to address without any premises stated.