Measles

Measles (from the Latin morbilli) is an acute, highly contagious viral disease characterized by a cyclical course, systemic intoxication, catarrhal inflammation of the mucosa of the respiratory tract and eyes, and a distinctive maculopapular rash. The causative organism is an RNA virus belonging to the genus Morbillivirus.

This airborne disease exhibits nearly 100 % susceptibility among non-immune individuals. Following infection, patients typically develop lifelong immunity. The introduction of routine measles vaccination has significantly reduced incidence rates; however, outbreaks continue to occur among unvaccinated populations.

Aetiology and pathophysiology

The primary source of infection is a person with active measles, who becomes contagious from the end of the incubation period until the fourth day after the rash appears. The virus enters the body through the mucous membranes of the upper respiratory tract, where it undergoes initial replication in lymphoid tissue.

It then enters the bloodstream (primary viremia) and disseminates throughout the body. Finally, the virus localizes in cells of the reticuloendothelial system, where it replicates further. Secondary viremia affects epithelial cells in the skin, conjunctiva, and respiratory tract, resulting in the primary clinical manifestations of the disease.

Clinical Significance

Measles follows a well-defined sequence of stages. Diagnosis is primarily based on the characteristic progression of symptoms. Treatment is symptomatic; vaccination remains the cornerstone of prevention.

The disease progresses through several distinct periods:

1. Incubation period. This stage lasts an average of 8 to 14 days and is asymptomatic.
2. Catarrhal (prodromal) period. This period lasts 3–4 days and presents with high fever, dry cough, rhinitis, and conjunctivitis (photophobia, tearing). Toward the end, pathognomonic Koplik spots (Belsky — Filatov — Koplik spots) appear on the buccal mucosa.
3. Exanthem period. This stage is characterized by a vivid maculopapular rash. A key diagnostic feature is its rigid progression in stages:
   • Day 1: Rash appears on the face and behind the ears.
   • Day 2: Rash spreads to the trunk.
   • Day 3: Rash appears on the arms and legs.
4. Pigmentation period. From the fourth day after rash onset, the rash fades in the same order in which it appeared, leaving behind brownish spots (residual pigmentation) and mild bran-like desquamation.

Differential Diagnosis

Measles must be differentiated from other exanthematous diseases: Rubella: Distinguished by milder catarrhal symptoms and lack of staged rash progression. Scarlet fever: Features a fine punctate rash on a hyperemic background, absence of conjunctivitis, and prominent pharyngitis with a “strawberry” tongue. Additional differential considerations include enteroviral exanthems, infectious mononucleosis, and allergic reactions.