That 40% likely applies fairly specifically geographically-speaking. There are other pathologies that degrade cognitive ability which are almost omni-present in developing nations. Hookworm, for instance, causes permanent IQ loss in children who are infected with it and it is nearly universal in Africa and many other places with inferior sanitation. The American US south had a big hookworm problem in the past, but intentional steps were taken to eliminate hookworm. The result was climbing average IQ scores across the south for nearly a century. Malaria also causes cognitive problems, not the least of which is causing missed school in children. Malaria, obviously, sees an awful lot of attention paid to it, but hookworm is not nearly as popular. If I could choose something to focus on, hookworm would probably come even before malaria in my mind. The negative cognitive effects of hookworm hamper everything that can be done to fight malaria and other things, preventing people from realizing how important hygeine and the like is.