The risk of human immunodeficiency virus (HIV) transmission during sexual activity is dependent on the infectivity of the HIV-positive individual and the susceptibility of the uninfected partner. HIV is most often transmitted during periods of high HIV load, but factors such as the type of sexual activity and the innate and genetic defenses of the uninfected partner exert a strong influence on the risk of transmission. Certain factors, such as coinfection with other sexually transmitted diseases or the presence of genital lesions in either sexual partner, amplify the risk of transmission that is predicted on the basis of sexual contact alone. In the absence of more-reliable options, such as a vaccine, factors that define HIV infectivity and susceptibility and factors that amplify the risk of HIV transmission, may serve as critical targets for containment of the HIV epidemic
An estimated 300 million cases of malaria occur each year, annually accounting for 1.5 to 2.7 million deaths (1). Most of these deaths are due to infection with Plasmodium falciparum and occur among children and pregnant women in the developing world, especially sub-Saharan Africa. Unfortunately, mortality during severe or complicated malaria still exceeds 10% to 30% (2). Due to increasing resistance among malaria parasites to chemotherapeutic agents, dissolution of malaria control programs, and increasing international travel, the incidence of malaria is increasing worldwide. Large scale multinational efforts have been initiated to “roll back malaria,” including major commitments of financial, clinical, and research resources (3,4).
