Measles Virus

Measles (also known as rubeola) is caused by a single-stranded, linear, negative-sense RNA virus of the family Paramyxoviridae and the genus Morbillivirus. It is highly contagious and spreads only among humans by respiratory droplets or direct-contact transmission from an infected person. Typically a disease of childhood, measles classically starts with cough, coryza, and conjunctivitis, followed by a maculopapular rash. Complications include diarrhea, pneumonia, and encephalitis. Measles can be prevented through vaccination, and thanks to this, had largely been eradicated until recent years. Most cases are managed with supportive care, although in select patients, antivirals can be indicated.

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RNA Viruses Flowchart Classification

RNA virus identification:
Viruses can be classified in many ways. Most viruses, however, will have a genome formed by either DNA or RNA. RNA genome viruses can be further characterized by either a single- or double-stranded RNA. “Enveloped” viruses are covered by a thin coat of cell membrane (usually taken from the host cell). If the coat is absent, the viruses are called “naked” viruses. Viruses with single-stranded genomes are “positive-sense” viruses if the genome is directly employed as messenger RNA (mRNA), which is translated into proteins. “Negative-sense,” single-stranded viruses employ RNA dependent RNA polymerase, a viral enzyme, to transcribe their genome into messenger RNA.

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General Characteristics

  • Genus: Morbillivirus
  • Family: Paramyxoviridae
  • Single-stranded, linear, negative-sense RNA virus
  • Enveloped virus
  • Large helical capsid carries RNA-dependent RNA polymerase in virion.
3D graphic representation of a spherical-shaped, measles virus particle

Three-dimensional graphic representation of a spherical-shaped measles virus particle

Image: “21074” by Allison M. Maiuri. License: Public Domain

Epidemiology and Pathogenesis


  • Incidence: 50–300/year in the United States
  • Mainly a childhood disorder
  • Since 2-dose measles, mumps, rubella (MMR) vaccination, US cases ↓ 99%
  • Incidence: males = females
  • Higher mortality observed in women at all ages
  • Fatality rate 4%–10% in developing countries


  • Highly contagious → 90% secondary infection rate: CDC–reportable disease
  • Humans are the only known reservoir.
  • Vectors:
    • Respiratory droplets
    • Person-to-person contact
    • Fomites
  • Young children and pregnant women are particularly susceptible to infection.

Clinically relevant species

  • Paramyxoviridae family:
    • Paramyxovirus: includes parainfluenza viruses and mumps virus
    • Pneumovirus: includes respiratory syncytial virus
    • Morbillivirus: includes measles virus
  • Paramyxoviridae family causes 30%–40% of all acute respiratory infections in infants and children.


  • Incubation period: 2–3 weeks
  • Virus enters via upper respiratory tract → infects local lymphatic tissues → amplification in regional lymph nodes → dissemination to various organs (testes, ovaries, thyroid gland, pancreas, and central nervous system)
  • 2 envelope glycoproteins bind to host cells: 
    • Hemagglutinin (H)
    • Fusion protein (F)
  • Negative-sense strand ssRNA (single-stranded RNA) used as template strand for positive strand
  • ssRNA translated by host ribosomes → produces proteins
  • Viruses are packaged while host cells undergo lysis.
  • Generalized immunosuppression: 
    • Suppression of interferon production through nonstructural proteins V and C
    • ↓ In delayed-type hypersensitivity
    • ↓ Interleukin (IL)-12 production
    • ↓ Antigen-specific lymphoproliferative responses

Clinical Presentation

Clinical presentation

  • Prodromal stage:
    • Cough
    • Coryza
    • Conjunctivitis
    • Photophobia
    • High fever
  • Day 3: Koplik’s spots (bluish-gray grain of salt with red halo, 1–2 days)
  • Day 4: maculopapular rash (from head/neck → body)


At least 1 complication occurs in 30% of cases:

  • Immune suppression and secondary infection:
    • Secondary infection can be with viruses or bacteria.
    • Tuberculosis reactivation has been described.
  • Diarrhea:
    • Most common
    • Seen in 8% of cases
  • Pneumonia:
    • Most deadly complication
    • Seen in 6% of cases
  • Otitis media
  • Giant cell pneumonia: 
    • Seen in individuals with cellular immunity deficiencies (e.g., leukemia, AIDS)
    • Often fatal
  • Acute disseminated encephalomyelitis (ADEM):
    • Postinfectious inflammation of central nervous system
    • Symptoms include weakness, fatigue, and blindness.
  • Subacute sclerosing panencephalitis:
    • Fatal degenerative disease of CNS
    • Occurs 7–10 years after infection
    • Poorly understood
  • Blindness: due to keratitis and corneal ulceration


The disease is diagnosed on clinical suspicion followed by confirmatory laboratory testing. Suspected cases should be isolated until confirmed.

  • History reveals trio of symptoms: cough, coryza, conjunctivitis
  • Exam confirms maculopapular rash.
  • Diagnosis made by 1 of 3:
    • Hemagglutination inhibition:
      • Rapid ↑ in IgG titers
      • Positive IgM
    • RT-PCR with detection of measles RNA
  • Consider lumbar puncture if concern for encephalitis.
  • Consider chest X-ray in patients with hypoxia and concern for pneumonia.



  • Supportive care:
    • Fever reduction
    • Rehydration
    • Superinfection prevention measures
  • High-dose vitamin A:
    • In patients with known nutritional deficiencies
    • 2-dose IM injection has been shown to ↓ morbidity and mortality in children < 5 years of age
  • Ribavirin:
    • Used in cases of pneumonia
    • Reduces duration of symptoms and hospitalization
    • Reduces morbidity and mortality
  • Vaccination counselling


  • MMR triple vaccine:
    • Children should get 2 doses.
    • 1st dose at 12–15 months and 2nd at 4–6 years
    • Can be given to all ages
  • MMRV vaccine (measles, mumps, rubella, and varicella):
    • Children up to age 12 should get 2 doses.
    • Only approved for children who are 12 months to 12 years of age
    • 1st dose at 12–15 months and 2nd dose at 4–6 years
  • Infection gives lifelong immunity.

Comparison of Common Childhood Rashes

Table: Comparison of common childhood rashes
NumberOther names for the diseaseEtiologyDescription
1st disease
  • Measles
  • Rubeola
  • 14-day measles
  • Morbilli
Measles morbillivirus
  • Cough, coryza, conjunctivitis
  • Koplik’s spots (blue-white spots with a red halo) on the buccal membrane
  • Maculopapular rash begins on the face and behind the ears → spreads to trunk/extremities
2nd disease
  • Scarlet Fever
  • Scarlatina
Streptococcus pyogenes
  • Sandpaper-feeling maculopapular rash that begins on the neck and groin → spreads to trunk/extremities
  • Dark, hyperpigmented areas, especially in skin creases, called Pastia’s lines
  • Strawberry tongue: coated white membrane through which swollen, red papillae protrude
3rd disease
  • Rubella
  • German measles
  • 3-day measles
Rubella virus
  • Asymptomatic in 50% of cases
  • Fine macular rash on the face (behind the ears) → spreads to the neck, trunk, and extremities (spares palms/soles)
  • Forscheimer’s spots: Pinpoint red macules and petechiae can be seen over the soft palate/uvula.
  • Generalized tender lymphadenopathy
4th disease
  • Staphylococcal scalded skin syndrome
  • Filatow-Dukes’ disease
  • Ritter’s disease
Due to Staphylococcus aureus strains that make epidermolytic (exfoliative) toxin
  • Some believe that 4th disease is a misdiagnosis and, thus, nonexistent.
  • The term was dropped in the 1960s and is only used for medical trivia today.
  • Begins with a diffuse erythematous rash that usually starts around the mouth → fluid-filled bullae or cutaneous blisters → rupture and desquamate
  • Nikolsky’s sign: Applying pressure on the skin with a finger (stroking) results in sloughing off of upper layers.
5th diseaseErythema infectiosumErythrovirus or parvovirus B19 (Primate erythroparvovirus 1)
  • Facial erythema (“slapped-cheek” rash) that consist of red papules on the cheeks
  • Begins on the face → spreads to the extremities → extends to trunk/buttocks
  • Initially confluent, then becomes net-like or reticular as it clears
6th disease
  • Exanthem subitum
  • Roseola infantum
  • Rose rash of infants
  • 3-day fever
Human herpesvirus 6B or 7
  • Sudden onset of high fever
  • Nagayama spots: papular spots on the soft palate/uvula
  • Rash begins as fever resolves (the term “exanthem subitum” describes “surprise” of rash after the fever subsides).
  • Numerous rose-pink, almond-shaped macules on the trunk and neck → sometimes spreads to face/extremities


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  2. Richardson M, et al. (2001). Evidence base of incubation periods, periods of infectiousness and exclusion policies for the control of communicable diseases in schools and preschools. Pediatr Infect Dis J. 20(4),380–391. 
  3. Zenner D, Nacul L. (2012). Predictive power of Koplik’s spots for the diagnosis of measles. J Infect Dev Ctries. 6(3),271–275. 
  4. Cherry JD. (2009). Measles virus. In: Textbook of Pediatric Infectious Diseases, 6th ed. Feigin RD., et al. (Eds.). Saunders. Philadelphia. pp.2427.
  5. Atkinson W, Wolfe C, Hamborsky J. (Eds.). (2011). Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book), 12th ed. The Public Health Foundation. Washington, DC.
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  7. Chen, S. (2019). Measles. Emedicine. Retrieved February 5, 2021, from:

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