Dr. Ryan's research focuses on clinical studies of illnesses associated with residing in, immigrating from, or traveling through resource-limited settings. His research is funded by the U.S. National Institute of Allergy and Infectious Diseases (NIAID) and the U.S. Centers for Disease Control & Prevention (CDC). Dr. Ryan is the principal investigator on research projects focusing on enteric vaccine and diagnostic development and host-pathogen studies on V. cholerae (the cause of cholera), Salmonella enterica serovar Typhi (the cause of typhoid fever), and Shigella spp. (a cause of bacillary dysentery). Particular areas of focus include the application of high throughput genomic, proteomic, immunoproteomic, and web-based platform technologies to these illnesses. Dr. Ryan is also the Director of Global TravEpiNet (GTEN), a CDC-sponsored national consortium focusing on global infectious diseases and evaluating vaccination strategies and use among global international travelers, as well as the acquisition of highly drug resistant bacteria during travel. He is the principal investigator and program director for a Fogarty International Center, National Institutes of Health (NIH)-sponsored Training Program in Vaccine Development and Public Health between Harvard-MGH and the ICDDR,B in Dhaka, Bangladesh. Dr. Ryan teaches tropical medicine and infectious diseases in the core curricula at Harvard Medical School, Harvard School of Public Health, and Harvard College, teaches students, residents and fellows at the MGH, and teaches in a number of post-graduate courses at Harvard Medical School and internationally.