Epidemic – n. (medical) an occurrence in which a disease spreads very quickly and affects a large number of people

Habitat – n. place where a plant or animal naturally or normally lives or grows

Infectious – adj. capable of being passed to someone else by germs that enter the body

Contaminate – v. to make (something) dangerous, dirty, or impure by adding something harmful or undesirable to it

Ecosystem – n. everything that exists in a particular environment

Bubonic Plague – n. a very serious disease that is spread especially by rats and that killed many people in the Middle Ages