What is Measles?

Measles is a respiratory disease caused by a paramyxovirus, genus Morbillivirus, with a single-stranded RNA core.⁽¹⁾ Measles is highly contagious and causes a systemic infection that begins in the nasopharynx. The virus is highly contagious, but can be easily destroyed by light, high temperatures, UV rays or disinfectants.⁽²⁾ Measles viruses are divided into eight clades (A to H), and although 24 genotypes have been confirmed, only 1990 have been identified since 19.⁽³⁾

Measles causes a systemic infection that begins in the nasopharynx. The virus is transmitted through respiratory secretions (nose secretions, coughs and sneezes), and an infected person is contagious for four days before symptoms appear until four days after the onset of the rash.⁽⁴⁾

Before the first measles vaccine was licensed in the United States in 1963, measles cases and outbreaks typically occurred in late winter and spring, usually every two to three years.⁽⁷⁾

Measles symptoms begin 10-14 days after close contact with an infected person. Symptoms begin with a fever, cough, runny nose, conjunctivitis, and white patches in the mouth, and progress to a rash that starts on the face, spreads to the rest of the body, and lasts for about a week.⁽⁸⁾ Before the measles rash appears (on the fourth or fifth day after the onset of fever), measles can be mistaken for several illnesses, including influenza, bronchiolitis, croup, or pneumonia.⁽⁹⁾

Other symptoms of measles are:⁽¹⁰⁾

• Sensitivity to light
• watery eyes
• sneezing
• body aches
• Swollen eyelids

Complications of measles include very high fever, diarrhea, otitis media, pneumonia, encephalitis and are reported in one-tenth of 1% of cases. Very rarely, subacute sclerosing panencephalitis (SSPE - a progressive, debilitating, and life-threatening brain disorder) and death also occur.^(11-12) Measles in pregnancy can cause a premature birth or a low birth weight infant.⁽¹³⁾ Recovering from measles creates antibodies that confer long-lasting immunity.⁽¹⁴⁾

In the past, when measles infections were common, doctors diagnosed measles by the presence of tiny white dots surrounded by a red halo on the inside of the cheeks of an infected person's mouth.¹⁵⁾ However, because measles is no longer common, measles rash has often been misdiagnosed by doctors as scarlet fever, Kawasaki disease, and dengue.⁽¹⁶⁾

"Modified" measles can also occur in people with some degree of immunity, as well as previously vaccinated people who get a milder form of measles. "Atypical" measles can occur in a person previously vaccinated with a killed-virus vaccine used from 1963 to 1967 and who is exposed to wild-type measles.⁽¹⁷⁾ The course of atypical measles is generally longer than that of natural measles.⁽¹⁸⁾