Since I was out of pocket for a bit, I thought I might let this lie instead of responding late. But, since Dr. Harrell has brought this up, I decided to respond.
> See, you don't get it. I'll try to explain more clearly: > > There is *already* resistance. There wasn't, but in any area which > once had spraying, there is now resistance. Once resistance appears > in a population, it remains in that population at a low level, and > selection being the force it is, it only takes a tiny selection > pressure to raise that to a common or high level. I realize that this sort of thing does happen. I guess what I don't get is how this has happened in areas where the data appear not to indicate it. For example, let's consider South Africa, where spraying was discontinued in '96 and reintroduced in '01. I would like to refer to two pages at the South Africa Department of Heath websites: http://www.doh.gov.za/facts/stats-notes/2004/malaria.htm http://www.doh.gov.za/facts/index.html >From a chart on the first page of the 1st website, we see that malaria cases were relatively low through 91 (with 5 year intervals, we don't know when the rise was between '91 and '96), and in '96, showing a jump. The peak year was 2000, after which cases dropped. For those who don't see the website, the cases were under 5k/year before 96, about 30k in '96, about 65k in 2000, and dropping to about 13k/year in 2003. Since then, it's remained below 13k. In fact, referencing the second website, it fell to about 7k in 2005. It rose again to 12k/year in 2006, but the 2007 winter season, the peak for malaria, has been less than 40% of the 2005 numbers...so it doesn't seem that 2006 was the start of at trend. We also see at the first website that the timing of the rise and fall of cases coincided with the elimination of DDT spraying and the reintroduction of DDT spraying. > > there are, do they outweigh the benefits? > > This is the point: in areas where DDT has not been used in many > years, then you maybe have one or two shots with DDT before it's > useless again. So, if you want to do wall spraying, you need to use a > cocktail, of *at least* 3 insecticides, at least 2 of which should be > novel. I may be misinterpreting what you mean by "many years" and "one or two shots", but it sounds like a year or two of effectiveness after a decade or two when it wasn't used. DDT wasn't used in South Africa for 5 years ('96-'00 and the utility of DDT spraying has been shown for more than 5 years after than (01-06 and the rainy season of '07). As a result, I would argue that the data from South Africa is inconsistent with the hypothesis: that ship has sailed. I don't know how many more decades that indoor spraying can be used effectively, but it is likely to be significantly longer than massive spraying is effective. From the data I've seen, I'd guess decades. But, that's just a guess...we need to continue to analyze data to know. Dan M. _______________________________________________ http://www.mccmedia.com/mailman/listinfo/brin-l
