Epidemic - An often sudden increase in the level of disease in a specific population over a given period of time.⏎
Fertilized Egg - Sometimes referred to as a zygote, this is the resulting initial cell formed when a sperm cell unites with an egg cell.⏎
Ecology - A branch of science that deals with the relation of organisms to one another and their physical environment.⏎
Contagion - A general term for any disease-causing infectious agent spread by direct or indirect contact.⏎