1. entomology pertaining to populations of plants, animals, and viruses that build up, often rapidly, to unusually and generally injuriously high levels —synonym outbreak —note many insect and other animal populations cycle (periodically or irregularly) between endemic and epidemic levels —see epizootic 2. pathology a disease sporadically infecting a large number of hosts in an area and causing considerable loss 3. pathology the quantitative progress of disease regardless of the initial or final amount, or of the rapidity of change —see infestation, pandemic, population dynamics This definition last updated 10/25/2008