The disease usually develops seven to 14 days after an exposure, but it can take up to 21 days (which is the length of quarantine). Once it develops, it’s marked by a high fever and a telltale rash that starts on the head and spreads downward. People are contagious for four days before the rash develops and four days after it appears. Complications can range from ear infections and diarrhea to encephalitis (swelling of the brain), pneumonia, death in up to 3 out of 1,000 children, and, in very rare cases, a fatal neurological condition that can develop seven to 10 years after the acute infection (subacute sclerosing panencephalitis).
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