DandyDon:The reason they don't is because they can't. From this July 2006 story: http://tfponline.com/absolutenm/templates/default.aspx?a=2524&template=print-article.htm
Do not think that is strictly true. You notice further down in the article it says:
(snip from same place):
Britain and parts of Europe already allow travelers to donate if blood tests show theyre free of malaria antibodies, immune cells that attack the parasite. Those tests arent used here because they detect just two of the four malaria species, albeit those that cause most disease
Not having figures of the relative percentages of the four types on hand, its difficult to say how important it is that only 2 of the 4 malarial species are detected. Mind you, antibodies are *not* "immune cells"....so the science is dodgy anyway.
There are a fair number of tests available that *could* be applied to screening, so its not the technology thats lacking. I would hazard a guess that its the *expense* of the screening that makes it easier to just rule those samples out than test them. However, as said, with increasing proportions of people going overseas, there will come a time when the development of a cheap test will make it worthwhile.
-j-