By John Donnelly, Globe StaffJOHANNESBURG, SOUTH AFRICA (SEPTEMBER 24, 2004) — Meeting in Nigeria four years ago, African leaders set a goal that 60 percent of children and pregnant women in malaria-affected areas around the continent would be sleeping under bed nets by the end of 2005.Today, fewer than 5 percent in those areas use the nets, which are coated with insecticide to kill mosquitoes that carry the deadly disease.