Measles (Rubeola)¶

Chapter 211 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Viral (incl. HIV) · Chapter 211

Key Clinical Points¶

Koplik's spots are pathognomonic of measles and appear on the buccal mucosa ~2 days before the rash.
Measles virus is antigenically monotypic, meaning vaccines developed decades ago remain protective worldwide.
Vitamin A supplementation (200,000 IU/day for 2 days) reduces morbidity and mortality in children with measles.
Measles induces a state of immunosuppression lasting weeks to months, increasing susceptibility to secondary bacterial infections.
CDC case definition requires generalized maculopapular rash, fever ≥38.3°C, and cough/coryza/conjunctivitis.
Measles case-fatality rate is 0.01–0.1% in developed countries but can be 5–10% or higher in endemic areas.
Post-measles encephalomyelitis occurs in ~1 in 1000 cases and is an autoimmune disorder triggered by the infection.
Measles vaccination is contraindicated in individuals with severe deficiencies of cellular immunity.
Secondary vaccine failure rates are estimated at ~5% but are likely lower when vaccination takes place after 12 months of age.
Measles is one of the most highly contagious directly transmitted pathogens, with secondary attack rates exceeding 90%.

1. DEFINITION & OVERVIEW¶

• Definition: Measles is a highly contagious viral disease characterized by a prodromal illness of fever, cough, coryza, and conjunctivitis followed by the appearance of a generalized maculopapular rash. • Historical Context: Before widespread vaccination, measles caused >2 million deaths annually worldwide. • Current Status: Vaccine eliminated endemic transmission in the US by 2000; however, imported cases and low coverage threaten this status (1274 cases reported in the US in 2019, the highest since 1992).

1.1 Global Considerations¶

• WHO Status: Americas region declared measles-free in 2016 but lost status due to outbreaks. • Progress: Global measles deaths decreased by 82% (772,854 to 136,216) from 2000–2022. • Impact: Vaccination prevented ~57.2 million deaths during this period. • Ongoing Risk: >100,000 children still die annually from measles despite progress.

2. EPIDEMIOLOGY¶

• Transmission: One of the most contagious pathogens; secondary attack rates >90% among susceptible contacts. • Mechanism: Transmission via respiratory droplets; no animal reservoirs. • Susceptibility: Newborns become susceptible when maternal antibodies wane (~6–9 months). • Outbreak Threshold: Outbreaks occur in populations with <10% immunity.

2.1 Transmission & Seasonality¶

• Patterns: Endemic measles has yearly seasonal epidemics superimposed on 2–5 year cycles. • Climate Impact: In temperate climates, outbreaks peak in late winter/early spring due to school gatherings and environmental factors. • Age Distribution: Shifts with vaccination coverage: infants (low-vaccine), school-age children (moderate), and adolescents/adults (high). • Healthcare Risk: Nosocomial transmission is common; isolation precautions and healthcare worker immunity are critical.

2.2 Impact of COVID-19¶

• Vaccine Gap: 40 million children missed measles vaccine doses in 2021 (25M first dose). • Outbreaks: Occurred in 22 countries (2021) and 37 countries (2022). • Trends: Measles cases/deaths increased by 18% and 43%, respectively, during this period.

3. ETIOLOGY & PATHOGENESIS¶

• Virus Type: Nonsegmented, negative-sense RNA virus in the Paramyxoviridae family. • Antigenic Stability: Antigenically monotypic; vaccines from decades ago remain effective.

3.1 Pathogenesis¶

• Initial Infection: Begins in respiratory mucosa/dendritic cells. • Viremia: Spreads virus systemically 2–4 days post-exposure. • Incubation Period: ~10 days to fever; 14 days to rash onset. • Immune Impact: Immunosuppression persists weeks/months post-infection, increasing susceptibility to secondary infections.

3.2 Immune Responses¶

• Innate Response: Includes NK cell activation and antiviral proteins. • Adaptive Response: Involves $ ext{IgM} → ext{IgG1/IgG3}$ switch and T-cell responses ( ext{Th1} → ext{Th2}). • Long-term Effect: Lifelong immunity follows wild-type infection, but induced immunosuppression impairs response to other antigens.

4. CLINICAL MANIFESTATIONS¶

• Clinical Progression: Prodromal fever/cough/conjunctivitis → Koplik's spots → generalized maculopapular rash.

4.1 Prodromal Phase¶

• Onset: Fever/malaise 10 days post-exposure. • Progression: Cough/coryza/conjunctivitis develop over 4 days.

4.2 Koplik's Spots¶

• Description: Pathognomonic bluish-white spots on buccal mucosa opposite lower molars. • Timing: Appear 2 days before rash; fade with rash onset.

4.3 Rash Progression¶

• Initial Site: Begins 2 weeks post-infection as erythematous macules behind ears/neck. • Spread: Progresses to face/trunk/extremities by day 2. • Resolution: Fades in reverse order over 3–4 days. • Additional Findings: Petechiae may occur; desquamation common in undernourished children.

5. DIFFERENTIAL DIAGNOSIS¶

• Rubella: Milder illness without cough; characteristic posterior auricular/suboccipital lymphadenopathy. • Roseola: Rash appears after fever subsides (exanthem subitum). • Infectious Mononucleosis: Atypical lymphocytosis contrasts with measles-associated leukopenia.

6. INVESTIGATIONS & DIAGNOSIS¶

• Clinical Assessment: Identification of Koplik's spots and rash progression pattern. • CDC Case Definition: 1. Generalized maculopapular rash (≥3 days). 2. Fever ≥38.3°C. 3. Cough/coryza/conjunctivitis.

6.1 Serology¶

• IgM: Single specimen confirms acute infection (detectable 4–5 days post-rash; undetectable by 4–8 weeks). • IgG: Four-fold rise between acute and convalescent sera is diagnostic.

6.2 Other Methods¶

• RT-PCR: Identifies genotypes and distinguishes wild-type/vaccine strains. • Virus Isolation: From respiratory secretions, blood, or urine. • Biopsy: Giant cell detection in biopsy specimens.

7. MANAGEMENT & TREATMENT¶

Supportive Care: • Hydration. • Antipyretic agents.
Antibiotics: • Indicated for bacterial complications (pneumonia, otitis media).
Vitamin A Supplementation: • ≥ 12 months: 200,000 IU/day imes 2 days. • 6–11 months: 100,000 IU/day imes 2 days. • < 6 months: 50,000 IU/day imes 2 days. • Follow-up: Third dose 2–6 weeks later for vitamin A deficiency.
Ribavirin: • Anecdotal use in immunocompromised/pregnant patients with pneumonia or encephalitis; not conclusively proven effective in clinical trials.

8. COMPLICATIONS & PROGNOSIS¶

• Respiratory Complications: Giant cell pneumonitis (immunocompromised); acute laryngotracheobronchitis (croup) with airway obstruction risk. • CNS Complications: • Post-measles encephalomyelitis: ~1/1000 cases; fever, seizures, neurologic deficits (autoimmune, not viral). • SSPE: Progressive cognitive/motor decline 5–15 years post-infection (common in <2-year-olds). • Prognosis: • Case-fatality rate: 0.01–0.1% in developed countries; 5–10% or higher in endemic areas. • Vaccination Effect: Previously vaccinated individuals experience milder disease.

9. PREVENTION & VACCINATION¶

• Active Immunization: Two-dose MMR vaccine (12–15 months, 4–6 years) provides lifelong immunity. • Passive Immunization: IgM/IgG antibodies from maternal vaccination or immunoglobulin administration provide short-term protection. • Vaccine Characteristics: Live attenuated virus; requires cold chain; secondary failure rate ~5% (lower if administered after 12 months).

Table 210-3: Recommendations for Poliovirus Vaccination of Adults Note: Included from source data. 1. Most adults in the United States have little risk for exposure to polioviruses, and most are immune as a result of vaccination during childhood. Vaccination with IPV is recommended for those at greater risk for exposure to polioviruses than the general population: a. travelers to areas or countries where polio is epidemic or endemic; b. laboratory workers who handle specimens that might contain polioviruses; c. health care workers or other caregivers who have close contact with patients who might be excreting wild-type polioviruses; and d. adults who are identified by public health authorities as being part of a group or population at increased risk because of an outbreak. 2. Adults who are unvaccinated or whose vaccination status is unknown and who are at increased risk should receive three doses of IPV. Two doses of IPV should be administered at intervals of 4–8 weeks; a third dose should be administered 6–12 months after the second. 3. Adults who have had a primary series of polio vaccine and who are at increased risk should receive another dose of IPV. Currently, data do not indicate a need for more than a single lifetime booster dose with IPV for adults.

10. KEY PEARLS & CLINICAL TRAPS¶

• Koplik's spots: Pathognomonic; appear on buccal mucosa ~2 days before rash. • Vitamin A: Supplementation (200k/100k/50k based on age) reduces mortality. • Immune Suppression: Lasts weeks to months post-infection. • Post-measles encephalomyelitis: Autoimmune, not viral; ~1/1000 cases. • SSPE: Occurs 5–15 years post-infection in children <2 years old. • CDC Definition: Rash ≥3 days, Fever ≥38.3°C, Cough/coryza/conjunctivitis. • Transmission: Highly contagious; secondary attack rates >90%.

Reference Tables¶

TABLE 210-3 Recommendations for Poliovirus Vaccination of Adults 1. Most adults in the United States have little risk…¶

Harrison's 22e, p.1638

1. Most adults in the United States have little risk for exposure to polioviruses,
  and most are immune as a result of vaccination during childhood.
  Vaccination with IPV is recommended for those at greater risk for exposure
  to polioviruses than the general population:
  a. travelers to areas or countries where polio is epidemic or endemic;
  b. laboratory workers who handle specimens that might contain polioviruses;
  c. health care workers or other caregivers who have close contact with
  patients who might be excreting wild-type polioviruses; and
  d. adults who are identified by public health authorities as being part of a
  group or population at increased risk because of an outbreak.
  2. Adults who are unvaccinated or whose vaccination status is unknown and
  who are at increased risk should receive three doses of IPV. Two doses of
  IPV should be administered at intervals of 4–8 weeks; a third dose should be
  administered 6–12 months after the second.
  3. Adults who have had a primary series of polio vaccine and who are at
  increased risk should receive another dose of IPV. Currently, data do not
  indicate a need for more than a single lifetime booster dose with IPV for
  adults.