DEFINITION AND MICROBIOLOGY
Measles is a highly contagious disease that is characterized by a prodromal illness of fever, cough, coryza, and conjunctivitis followed by a generalized maculopapular rash. Measles is caused by a nonsegmented, single-strand, negative-sense RNA virus of the genus Morbillivirus and the family Paramyxoviridae.
Humans are the only reservoir for measles virus; unvaccinated infants who have lost maternal antibodies account for the bulk of susceptible individuals. However, as measles vaccine coverage increases, the age distribution of the disease shifts upward, with more adolescents and adults affected. The World Health Organization (WHO) Region of the Americas eliminated endemic measles in 2016.
Routine administration of the measles vaccine has markedly reduced worldwide mortality due to measles; in 2015, there were ∼134,200 deaths.
Pts are contagious for several days before and after the rash appears. The virus is spread primarily via respiratory droplets over short distances. Secondary attack rates among susceptible contacts are >90%.
Approximately 10 days after infection with measles virus, pts develop fever and malaise, followed by cough, coryza, and conjunctivitis; the characteristic rash occurs 14 days after infection.
An erythematous, nonpruritic, maculopapular rash begins at the hairline and behind the ears, spreads down the trunk and limbs to include the palms and soles, can become confluent, and begins to fade (in the same order of progression) by day 4.
Koplik’s spots are pathognomonic for measles and consist of bluish-white dots ∼1 mm in diameter surrounded by erythema. They appear on the buccal mucosa ∼2 days before the rash appears and fade with the onset of rash.
Pts with impaired cellular immunity may not develop a rash and have a higher case–fatality rate than those with intact immunity.
Complications include giant-cell pneumonitis, secondary bacterial infection of the respiratory tract (e.g., otitis media, bronchopneumonia), and CNS disorders.
– Postmeasles encephalitis occurs within 2 weeks of rash onset in ∼1 in 1000 cases and is characterized by fever, seizures, and a variety of neurologic abnormalities.
– Measles inclusion-body encephalitis (MIBE) and subacute sclerosing panencephalitis (SSPE) occur months to years after acute infection and are caused by persistent measles virus infection.
MIBE is a fatal complication that primarily affects pts with defects in cellular immunity.
SSPE is a progressive disease characterized by seizures and deterioration of cognitive and motor functions, with death occurring 5–15 years after measles virus infection.
The characteristic rash and pathognomonic Koplik’s spots permit a clinical diagnosis.
Serologic testing is the most common method of laboratory diagnosis. Measles-specific IgM is usually detectable within 1–3 days of rash onset.
Viral culture and reverse-transcription PCR analysis of clinical specimens are used occasionally to detect measles.