Definition: Measles (also known as Rubeola) is a highly contagious viral infection caused by the Morbillivirus genus and has a human-only reservoir.
Transmission:
Measles virus spreads through respiratory droplets via direct contact or indirectly through fomites.
Extremely contagious: 99% chance of infection with close contact.
High incidence before vaccinations: 90% of children contracted the disease by age 10.
Case Statistics in the U.S.
Measles cases (2010-2019): Reports of cases fluctuated significantly, peaking at 981 cases in 2019.
2025 Projections: 800 total cases are expected with the following age distribution:
Under 5 years: 31% (249 cases)
Ages 5-19 years: 38% (304 cases)
20 years and older: 29% (231 cases)
Unidentified age: 2% (16 cases)
Vaccination Status:
96% of cases unvaccinated or unknown status.
Only 1% received one dose of the MMR vaccine, and 2% had two doses.
Hospitalization:
11% of cases (85 out of 800) required hospitalization:
19% of infants under 5 years were hospitalized.
6% in the over 20 years category.
Reported Deaths: Track trends in reported measles cases and deaths post-2010 with emphasis on peaks in outbreaks.
Historical Context
Major Events:
1963: Introduction of the inactivated measles vaccine.
1968: Development of the live measles vaccine.
1971: Recommendation for the double dose of MMR (Measles, Mumps, Rubella).
1990: Notable spike in reported cases.
Pathogenesis of Measles
Overview: Measles virus replicates in the respiratory epithelium and lymph nodes, leading to systemic dissemination.
Viral Lifecycle: Starts with exposure to virus via respiratory airways, captured by dendritic cells and macrophages; viral RNA is released, goes through cell cytoplasm, ultimately leading to release and budding of new viral particles.
Immune Response:
First symptoms occur 10-14 days post-exposure (prodromal phase): Fever, cough, runny nose, conjuntivitis, Koplik spots seen in the mouth.
Risk of secondary infections due to immune suppression following measles infection, affecting memory cells.
Complications of Measles
Spectrum of Complications: Includes diarrhea, otitis media, pneumonia (which can be fatal), and encephalitis.
CNS Involvement: Significant portion of cases lead to neurological complications such as:
Encephalitis: Severe complication with risk of permanent cognitive impairment.
SSPE (Subacute Sclerosing Panencephalitis): Progressive neurological disorder, with 100% fatality, occurring in 1 in 10,000 cases; symptoms manifest years after initial measles infection.
Mortality Rates: Notable risk for pneumonia (>90% fatality), encephalitis (up to 20% mortality).
Herd Immunity: Measles requires a high level of herd immunity (83-94%) due to its high R0 (12-18); vaccination is crucial for community protection.
Measles Vaccine and Herd Immunity
Vaccination: Critical to prevent outbreaks and maintain population immunity levels. The MMR vaccine prevents the initial infection as well as serious complications.
Herd Immunity Threshold: Achievable through widespread vaccination, crucial to protect individuals who cannot be vaccinated due to medical reasons (infants, immunocompromised).
Conclusion
Public Health Measures: Continued vaccination efforts are necessary to control measles outbreaks and protect public health. Vaccination rates should be closely monitored, and educational efforts to demonstrate the importance of herd immunity are essential.