Endemic Burkitt's lymphoma (eBL) is the most common childhood cancer in Equatorial Africa. Two cofactors are linked to the etiology of this pediatric cancer: Epstein-Barr virus (EBV) infection, and sustained and intense exposure to Plasmodium falciparum malaria (holoendemic malaria). While there is a wealth of epidemiologic data establishing both EBV and P. falciparum as co-carcinogens necessary for the emergence of eBL, the mechanisms by which these pathogens interact and their unique roles in the etiology of this malignancy remain unknown. In this application, we will test three inter-related hypotheses: 1) children infected with P. falciparum before primary EBV infection will have a higher viral load and increases in viral load will occur throughout infancy and early childhood and correlate with the frequency and intensity of malaria exposure;2) repeated P. falciparum infections throughout infancy and early childhood results in the loss of an established EBV-specific anti-viral CD8+ T cell response and 3) repeated P. falciparum infections throughout infancy and early childhood result in the expansion of the peripheral B cell pool and the emergence of a pre-malignant BL B-cell phenotype. We will test these hypotheses by determining how P. falciparum infections modulate EBV immunity and persistence in a longitudinal study of children followed from 1 month through 3 years of age. To examine the effects of malaria exposure, two populations of children with divergent exposures to malaria (e.g. holoendemic and sporadic) living in Western Kenya will be compared to achieve the objectives of this study which are: 1) to identify the age of EBV and P. falciparum infections, and determine the effects of repeated P. falciparum infections on the establishment and maintenance of EBV infection;2) to determine the EBV-specific CD8+ T cell response of children with divergent malaria exposures and 3) to determine the influence of holoendemic malaria on blood B cell subpopulations and homeostasis in children.