Infectious diseases are usually discussed in the language of cells, pathogens, and populations. Yet every infection begins much earlier, at a scale that is rarely addressed directly the scale of atoms, energy transfer, and molecular transformation. At this level, disease is not a clinical event but a chemical one. This keynote examines infectious diseases from the perspective of radiochemistry, where radioactive tracers and nuclear techniques allow biological processes to be followed with exceptional sensitivity. Radiochemical methods are expected to explore early molecular events in infection, long before symptoms appear, and to track subtle post-infection changes that may persist even after apparent recovery. These approaches have clear relevance for prophylactic strategies, diagnostic precision, and the evaluation of therapeutic response.

Radiochemistry also offers a unique advantage in studying pathogen–host interactions. By tracing molecular pathways rather than end-stage outcomes, it becomes possible to identify vulnerable stages in infection where intervention can be both early and targeted. This is particularly important in an era where resistance, latency, and long-term complications increasingly challenge conventional approaches. In the final part of the lecture, infectious disease is placed within a wider chemical context. The same molecular principles that govern infection and immunity once governed the emergence of life itself. From prebiotic chemistry to self-organizing molecular systems, life arose from interactions that were chemical before they were biological. Understanding disease at the molecular level, therefore, does more than improve treatment it reconnects modern medicine with the deeper chemical logic of life. By moving deliberately from atoms to organisms, this talk argues for a broader, integrative view of infectious disease one in which chemistry is not a supporting discipline, but a foundational one.

Shree Niwas Chaturvedi holds a Ph.D. in Nuclear and Radiochemistry from the Department of Chemistry, Banaras Hindu University, India. His doctoral work examined chemical effects of nuclear transformations in iodine compounds and indium complexes. He remains engaged in research, science education, and outreach.