Harvard University's School of Public Health said it received $25 million from Microsoft Corp.'s co-founder and chairman, Bill Gates, and his wife to study AIDS prevention in Nigeria. The Nigerian initiative will begin by profiling the nature of HIV infection in Africa's most populous country, said Barry Bloom, dean of the school, which already has a similar program in Senegal. "The object, based on our experience in Senegal, is to prevent infection from getting to the level of 25% to 30% as in other African nations," Bloom said. Senegal's infection rates have remained stable at 2%. Preventing the spread of deadly diseases among poor children is a chief priority of the Seattle-based Bill & Melinda Gates Foundation, which has an asset base of $21 billion.