Microsporidia: evolution, infection mechanisms and host impact.

Microsporidia are obligate intracellular eukaryotic parasites. These pathogens belong to an understudied lineage of fungi and can infect most types of animal. Although microsporidia were first discovered over 150 years ago, their impact on humans and agriculturally important animals has become clear only within the last several decades. Microsporidia have the smallest known eukaryotic genomes, and technological advances have been used to highlight the consequences of genomic reduction. Microsporidia have a unique structure known as the polar tube and the mechanisms of how this infectious apparatus is used for invasion of host cells are beginning to be understood. Microsporidia infection has wide-ranging consequences on hosts, and in turn, hosts have evolved immunity against these parasites. Progress has been made in both detecting and treating these infections. This Review provides an overview of the evolution, infection mechanisms and impact of these parasites on their hosts.