communicability period /kəmyo̅o̅′nəkəbil″itē/ , the time during which an infectious agent may be transferred directly or indirectly from an infected person to another person, from an infected animal to humans, or from an infected person to animals, including arthropods. For measles the communicability period ranges from 4 days before the appearance of a rash until 5 days after the onset of symptoms.