Microsporidia are a group of parasites composed of just a single cell, but are found to infect all known animals – including humans – and can be fatal to people with compromised immune systems, such as AIDS or transplant patients. Microsporidia grow and multiply inside their host cells, but they exist outside of their hosts as spores that can infect nearby cells. Dr. Naomi Fast is striving to understand the cellular signals that the parasite uses to infect cells. She is examining and comparing what genes are expressed before and after spores infect their hosts, to identify genes that are specifically activated during infection. Identifying these genes could point to potential targets for drug treatments.