PHRI faculty members pursue a range of infectious disease programs on bacteria, fungi and viruses. A major emphasis of research at PHRI is directed at understanding the molecular basis of disease by studying pathogens and host responses to these infectious agents in areas such as pathogenicity and virulence, vaccine development, rapid diagnostics, molecular epidemiology, drug resistance and drug discovery. The infectious diseases programs also include studies of clinical factors that result in disease propagation and transmission, as well as selection for enhanced pathogen virulence or drug resistance. Finally, PHRI has long-standing programs with model systems that explore fundamental aspects of immunology, gene expression, genomics, DNA/RNA replication and recombination, genetic competence, enzyme structure and function, and viral assembly and structure.