A person is not contagious during the incubation period. A person is mildly contagious when he or she first experiences symptoms. A person is most contagious about 4 days before the onset of the measles rash. Some risk of transmission lasts until about 4 days after the rash starts.
Symptoms occur several days before the rash begins. These can include:
- High fever (up to 105°F or 40.6°C)
- Hacking cough
- Muscle and body aches
- Red, watery eyes (pink eye)
- Runny nose
- Swelling of the eyelids
- Small red lesions with blue-white centers (known as Koplik's spots) appearing on the inside of the mouth.
The early symptoms usually disappear 1-2 days after the rash appears, although the cough may continue until all symptoms are gone. The measles rash is a red, blotchy rash that usually appears about 14 days after exposure to the virus, and lasts 5 to 6 days (see Pictures of Measles).
In order to make a diagnosis, the doctor will ask a number of questions (medical history) and perform a physical exam to look for signs or symptoms of measles. Diagnosing the condition can often be done just based on a person's symptoms and the findings of the physical exam. If the doctor is unsure, he or she may order a blood test to look for antibodies to the measles virus, or a throat culture to look for the virus itself.
Several other medical conditions can have signs or symptoms that are similar to measles. The doctor will consider these conditions before diagnosing measles. Some of these conditions include:
- German measles (rubella)
- Syphilis (a sexually transmitted disease)
- Scarlet fever
- Mononucleosis (mono)
- Toxoplasmosis (infection in tissue)
- Reaction to medications
- Kawasaki syndrome (disease in the membrane of the upper respiratory tract).