communicable disease, any disease transmitted from one person or animal to another directly, by contact with excreta or other discharges from the body; indirectly, by means of substances or inanimate objects, such as contaminated drinking glasses, toys, or water; or by means of vectors, such as flies, mosquitoes, ticks, or other insects. Communicable diseases may be caused by bacteria, chlamydia, fungi, parasites, rickettsiae, and viruses. To control a communicable disease, it is important to identify the organism, prevent its spread to the environment, protect others against contamination, and treat the infected person. Many communicable diseases, by law, must be reported to the local health department. Also called contagious disease.
