USMLE Guide: Measles

Introduction

Measles, also known as rubeola, is a highly contagious viral infection caused by the measles virus (MeV). It is characterized by a distinctive rash, fever, and respiratory symptoms. This USMLE guide aims to provide a comprehensive overview of measles, including its etiology, epidemiology, clinical presentation, diagnosis, treatment, and prevention.

Etiology

• Measles is caused by the measles virus, a member of the Paramyxovirus family.
• It is an enveloped, single-stranded RNA virus with a helical nucleocapsid.

Epidemiology

• Measles is a global health concern, although vaccination efforts have significantly reduced its prevalence.
• It primarily affects children under the age of 5, but individuals of any age can be infected if not vaccinated.
• Measles is highly contagious, spreading through respiratory droplets and direct contact with infected individuals.

Clinical Presentation

• Incubation period: 10-14 days.
• Prodromal phase:
  • High fever
  • Cough
  • Coryza (runny nose)
  • Conjunctivitis (red eyes)
• Koplik spots:
  • Small white spots with a blue-white center on the buccal mucosa, opposite the molars.
• Rash:
  • Begins around the hairline and spreads downward.
  • Maculopapular, erythematous rash.
  • Rash fades in the same order it appeared.
• Other symptoms:
  • Malaise
  • Lymphadenopathy
  • Photophobia

Diagnosis

• Clinical presentation is often sufficient for diagnosis.
• Serologic testing:
  • Detection of specific IgM antibodies against measles virus.
• Polymerase chain reaction (PCR) testing:
  • Detects viral RNA in respiratory specimens or urine.

Treatment

• No specific antiviral treatment for measles.
• Supportive care to manage symptoms:
  • Antipyretics for fever.
  • Plenty of fluids to maintain hydration.
  • Vitamin A supplementation in malnourished individuals.

Complications

• Otitis media
• Pneumonia
• Encephalitis
• Subacute sclerosing panencephalitis (SSPE)

Prevention

• Vaccination with the measles-mumps-rubella (MMR) vaccine.
• Two doses of MMR vaccine provide long-lasting immunity.
• Vaccination helps prevent outbreaks and protect vulnerable populations.
• Vaccination is contraindicated in certain individuals, such as immunocompromised patients.

Conclusion

Measles is a highly contagious viral infection that primarily affects children. Prompt recognition of the characteristic clinical presentation, along with appropriate management and prevention measures, is essential for controlling the spread of the disease. Understanding the etiology, epidemiology, clinical features, diagnosis, treatment, and prevention is crucial for healthcare professionals preparing for the USMLE exams.