Approximately 107,500 deaths, mostly in children under 5 years old.
Vaccination prevented ~60 million deaths between 2000-2023.
Virology
Family: Paramyxoviridae
Genus: Morbilivirus
Size: 150-300 nm
Envelope: Yes
RNA: Single-stranded, non-segmented
Nucleocapsid: Helical
Fusion protein: Present
Haemagglutinin: Present
Matrix: V
Negative-sense ssRNA, non-segmented.
Fusion protein (F)
Encodes 6 major structural proteins.
2 important transmembrane glycoproteins
Haemagglutinin (HA)
Strains:
Wild strain
Vaccine strain
Exists as single serotype, but nucleotide sequence analyses have identified distinct lineages.
Serotype 1
Natural host: Human
Transmission
The virus remains active and contagious in the air or on infected surfaces for up to 2 hours.
Transmission occurs through contact with infected secretions.
Airborne respiratory droplets are a common route.
Infectivity period: 4-5 days before rash to 4 days after rash onset.
Contagiousness
R_0 (basic reproduction number):
Ebola: 2-3
Flu: 1-4
SARS: 2-5
Mumps: 4-7
Polio: 5-7
Measles: 12-18
Risk Factors
No immunization
Immunocompromised individuals
Malnutrition
Crowded living conditions
Close contact with infected individuals
Low socioeconomic status
Very young age
Pathogenesis
Viral Attachment: Hemagglutinin (H) protein binds to host cell receptors:
CD46 (in non-immune cells)
SLAM (in immune cells)
nectin-4 (in epithelial cells).
Membrane Fusion and Viral Entry: Fusion (F) protein facilitates fusion between the viral envelope and the host cell membrane.
Conformational changes upon activation lead to membrane fusion.
Enables cell-to-cell fusion, forming syncytia, which contributes to viral spread and immune evasion.
The virus multiplies locally in the respiratory tract and then spreads to the regional lymph nodes.
Enters the bloodstream through infected monocytes (primary viremia).
Further multiplies in reticuloendothelial tissues and spills into the bloodstream (secondary viremia).
Disseminates to various sites, predominantly seeding in epithelial surfaces (skin, mucosa, conjunctiva).
The skin rash is immune-mediated due to infection of dermal capillary endothelial cells and immune complex formation.
Human CD46 molecule (respiratory epithelial cell) has been identified as a cellular receptor for measles virus.
Later, immune cells (macrophages, dendritic cells, T & B cells) become the primary target.
Infection progresses to affect the alveolar macrophages & dendritic cells that transport the virus to regional lymph nodes where T & B cells become infected.
Dissemination to other sites including the spleen, lymphatic tissue, liver, skin, and lungs follows.
Immunity
Antibodies raised against either viral haemagglutinin or fusion protein neutralize measles virus in vitro and protect against infection.
Both humoral and cellular measles-specific immunity are important for viral clearance.
Immunity is thought to be life-long.
Clinical Manifestation
Incubation period: 10-14 days (range 7-23 days).
Prodrome (4 days): Non-specific symptoms
Fever (up to 39°C).
Cough, coryza, conjunctivitis.
Malaise, vomiting, diarrhea
Koplik spots: Pathognomonic of measles; slightly raised, small bluish-white spots in buccal mucosa around first and second lower molar (2-3mm in diameter, erythematous base). "grains of salt on a red background”. Detection improve the accuracy of clinical diagnosis
Eruptive/Exanthem (Maculopapular rash):
Typically appears at the hairline on the face, then spreads to the upper neck, trunk, arms, and legs (centrifugal pattern).
Blanching rash.
Lasts for 5-6 days before fading.
On average, rash occurs 14 days after exposure.
Lymphadenopathy, high fever, pharyngitis, conjunctivitis.
Recovery: In uncomplicated measles, the disease improves by the 3rd day after rash onset; fully recovered 7–10 days after the onset of the disease. Cough may persist for one to two weeks after measles. The occurrence of fever beyond the 3rd to 4th day of rash suggests a measles-associated complication.
Clinical Spectrum
Classic measles: Immunocompetent individual
Atypical measles: Patients immunized with formalin-killed vaccine; rash begins on the extremities and spreads to the trunk and face; pneumonia with nodular pulmonary infiltrates.
Modified measles: Mild form of typical measles; pre-existing antibody levels below the protective level.
Diagnosis
Clinical diagnosis based on history & findings on physical examination.
Laboratory diagnosis:
Leukopenia, lymphocytosis.
Blood: anti-measles virus IgM antibodies by ELISA.
Nasopharyngeal swab, conjunctiva swab, respiratory secretion, and urine: measles virus RNA by RT-PCR or viral culture Spectmen
Imaging: Chest X-ray
Complications
Approximately 30% of affected patients.
More likely in children under 5 years and adults over age 30; also in malnourished children (especially vitamin A deficiency), HIV, etc.
Acute laryngotracheobronchitis (croup), severe diarrhoea/dehydration, Giant-cell pneumonitis (Hecht’s pneumonia).
Histologic evaluation of conjunctival, nasopharyngeal, or buccal epithelial cells may demonstrate giant cells with inclusions; these cells may also be present in urine.