Measles is a respiratory disease caused by a paramyxovirus of the Morbillivirus genus, characterized by a single-stranded RNA core.⁽¹⁾ It is highly contagious and the infection originates in the nasopharynx. The virus can be destroyed by light, high temperatures, UV rays or disinfectants⁽²⁾. Measles virus strains are classified into eight clades (A to H), and although 24 genotypes have been confirmed, only 1990 have been identified since 19.⁽³⁾

Contagion occurs through respiratory secretions, such as nasal secretions, coughing and sneezing. An infected individual is contagious from four days before the onset of symptoms until four days after the onset of the rash.⁽⁴⁾

Measles symptoms appear 10-14 days after exposure and begin with fever, cough, rhinitis, conjunctivitis, and white patches in the mouth, progressing to a rash starting on the face and spreading to the body, persisting for about a week⁽⁷⁾. In the early days, measles can be confused with other illnesses including influenza, bronchiolitis, croup, or pneumonia⁽⁸⁾.

Other symptoms include: sensitivity to light, watery eyes, sneezing, body pain, swollen eyelids.⁽⁹⁾

Complications include high fever, diarrhea, otitis media, pneumonia, encephalitis and more rarely subacute sclerosing panencephalitis (SSPE)^(10-11). During pregnancy, measles can cause premature birth or low birth weight babies⁽¹²⁾. Recovery from measles leaves long-lasting immunity⁽¹³⁾.

Traditionally, measles was diagnosed by looking at the typical white dots on the inside of the cheeks⁽¹⁵⁾. However, as cases decline, diagnostic errors can confuse the measles rash with other conditions such as scarlet fever or 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⁾