Pathogens, microbial organisms that cause disease, represent an important category of invasive species. Invasive pathogens are those pathogenic microorganisms such as bacteria, fungi and viruses that disseminate to new habitats and pose the risk of disease to the plants or animals of that ecosystem. These exotic pathogens may be especially devastating if the host plant or animal species at risk of infection is immunologically naïve to it. Invasive pathogens may produce disease in a single species or a closely related group for species, such as the lethal fungal pathogen that causes Dutch elm disease in American elms and other elm trees. Invasive pathogens may also produce disease in a larger taxonomic group such as the viral hemorrhagic septicemia virus (VHSV) that causes disease in over 50 species of fishes. Our scientists work with partners on federal, state, and local levels to learn more about invasive pathogens and to help managers develop ways to prevent their spread and mitigate their impacts.