Description

• A highly communicable, acute viral illness characterized by an exanthematous maculopapular rash that begins at the head and spreads inferiorly to the trunk and extremities
• Rash is preceded by fever and the classic triad of cough, coryza, and conjunctivitis (3 Cs). Koplik spots are pathognomonic lesions of the oral mucosa early in the course of the infection.
• Public health problem in the developing world, with significant morbidity and mortality; rising incidence in developed nations with declining vaccination rates
• One dose of MMR vaccine is 93% effective, and 2 doses are 97% effective against measles.
• System(s) affected: hematologic; lymphatic; immunologic; pulmonary; skin
• Synonym(s): rubeola

Epidemiology

• Transmission: direct contact with infectious droplets; highly contagious; 90% of nonimmune close contacts likely to become infected on exposure
  • Droplets can remain airborne for hours.
• Infectivity is greatest during the prodromal phase.
  • Patients are considered contagious from 4 days before symptoms until 4 days after rash appears.
  • Immunocompromised patients are considered contagious for the entire duration of disease.
• Incubation period: averages 12.5 days from exposure to onset of prodromal symptoms
• Predominant age: varies based on local vaccine practices and disease incidence. In developing countries, most cases occur in children <2 years.

Incidence

• No longer considered an endemic disease in the United States; isolated outbreaks still occur.
• In 2019, measles cases surged worldwide to the highest number of cases in 23 years with over 850,000 cases globally, and global deaths climbed 50% since 2016.
• Although the number of measles cases was going down in 2020 due to COVID-19 control measures, measles campaigns in 26 countries were suspended due to the COVID-19 pandemic with 94 million children missing scheduled measles vaccine doses in 2020.
• The WHO and UNICEF are expecting more child deaths from measles than COVID-19 in Africa due to the measles campaigns disruption.
• Unvaccinated subpopulations and vaccine hesitancy have contributed to persistence of measles in the United States (1).

Etiology and Pathophysiology

The measles virus enters through the respiratory mucosa and replicates locally. It spreads to regional lymphatic tissues and other reticuloendothelial sites via the bloodstream.

• Measles virus is a spherical, enveloped, nonsegmented, single-stranded, negative-sense RNA virus of genus Morbillivirus, family Paramyxoviridae.
• Humans are the only natural host.

Risk Factors

• For developing measles:
  • Lack of adequate vaccination (2 doses)
  • Travel to countries where measles is endemic
  • Contact with exposed individuals
• For severe measles or measles complications:
  • Immunodeficiency
  • Malnutrition
  • Pregnancy
  • Vitamin A deficiency
  • Age <5 years or >20 years

General Prevention

• 100% preventable with proper vaccination
• Measles vaccine (active immunization)
  • Vaccine is usually given in combination with MMR or with added varicella (MMRV; ProQuad).
  • Primary vaccination requires 2 doses.
    • First dose at 12 to 15 months of age; 95% develop immunity.
    • Second dose at the time of school entry (4 to 6 years of age) or any time >4 weeks after first measles vaccine; the 5% of initial nonresponders almost always develop immunity after the second dose.
    • Health care workers should have immunity verified and, if not immune, should receive the vaccine if not contraindicated.
  • Common adverse reactions to the vaccine
    • Fever
    • Febrile seizures are rare (<5%) and occur 6 to 12 days after vaccination. Risk of febrile seizures increases if initial immunization is delayed past age 15 months (2).
    • Transient, mild, measles-like rash 7 to 10 days after vaccination (2%, with decreasing incidence during second vaccination)
    • If hypersensitivity reaction occurs, test for immunity; if immune, second dose not needed
    • There is no substantiated link between MMR vaccine and autism.
  • Contraindications
    • Live viral vaccines are contraindicated in immunosuppressed patients. For MMR, vaccinate asymptomatic HIV-infected children with adequate CD4 count.
    • Live vaccine is contraindicated in pregnancy (risk of fetal infection).
    • Anaphylactic reaction to gelatin or neomycin; consult an allergist before vaccination.
    • Egg anaphylaxis is not a contraindication.

Commonly Associated Conditions

• Immunosuppression
• Malnutrition