SILENT PLAGUE: A special report.; Deadly Shadow Darkens Remote Chinese Village
AIDS virus has devastated impoverished and remote Donghu, China, where some 80 percent of adults carry HIV and over 60 percent are already debilitated; depth of tragedy in villages like Donghu, something officials in Henan Province have generally insisted is not problem, is only now emerging as desperate, dying farmers have started to speak out; many farmers in province were infected in 1990's at government-owned collection stations where they sold their blood; virus has continued to spread through other routes because officials have blocked research and education drives; map; photos (M)