Taxonomy and morphology of the measles virus
The measles virus belongs to the family Paramyxoviridae, genus Morbillivirus. Its morphology is typical for paramyxoviruses: virion diameter is about 150 nm, spherical shape. The genome is represented by single-stranded unsegmented negative-sense RNA.
Structural components of the virion:
- Nucleocapsid of helical symmetry type, formed by nucleoproteins (N), inside which the negative-sense RNA is packaged;
- Matrix protein (M) lining the inner surface of the envelope;
- Lipoprotein envelope — the presence of a supercapsid makes the virus enveloped;
- Surface glycoproteins: hemagglutinin (H), fusion protein F, hemolysin;
- Replication enzymes (RNA-dependent RNA polymerase).
The virus exhibits hemagglutinating and hemolytic activity, whereas neuraminidase is absent. It shares common antigens with canine distemper and bovine rinderpest viruses.
Cultivation and resistance
Bacteriological nutrient media are not applicable to viruses—cell cultures are used instead. For the measles virus, optimal choices are primary trypsinized cell cultures of monkey and human kidneys, as well as continuous cell lines HeLa and Vero. Replication is assessed by the cytopathic effect: the appearance of intranuclear and cytoplasmic inclusions, as well as the formation of symplasts—giant multinucleated cells formed due to the activity of the F protein.
In the external environment, the virus is unstable: at room temperature, it is inactivated in 3–4 hours and rapidly killed by sunlight, ultraviolet radiation, detergents (including soap), and disinfectants. In laboratory animals, the infection is reproduced primarily in monkeys.
Epidemiology
Measles is an anthroponotic infection: the sole source is an infected human. The leading transmission mechanism is aerosol (airborne), less commonly contact. Maximum virus shedding occurs during the catarrhal period.
- Susceptibility is universal;
- Contagiousness index is 100%;
- A patient is contagious from the last two days of the incubation period until the 4th day after the appearance of the rash;
- Post-infection immunity is lifelong and robust.
Pathogenesis
The incubation period is 8–16 days. The entry portal is the mucous membrane of the upper respiratory tract and conjunctiva. The virus has a tropism for the epithelium of the respiratory and gastrointestinal tracts. Starting from the 3rd day of incubation, primary viremia develops: the pathogen enters the blood, is carried to organs of the reticuloendothelial system, replicates there, and re-enters the bloodstream — forming secondary viremia. By the 5th day after the appearance of the rash, virus-neutralizing antibodies are detected in the blood. A transient immunodeficiency state develops against the background of the infection, which explains frequent bacterial complications.
Clinical presentation
Measles is an acute, highly contagious disease characterized by a combination of the following syndromes:
- Fever and intoxication: elevated temperature, malaise, lethargy, tearfulness;
- Catarrhal syndrome: rhinitis with mucous discharge, hyperemia and spotting of the buccal mucosa (preceding Koplik's spots), coarse "barking" cough, hoarseness;
- Conjunctivitis: eyelid edema, photophobia, lacrimation — forming the patient's characteristic "tearful" appearance;
- Exanthem syndrome: maculopapular rash progressing to pigmentation and desquamation, characterized by sequential rash spread — day 1 face (bridge of the nose, retroauricular area) and neck, day 2 trunk and proximal upper extremities, days 3–4 distal extremities.
The main threat is the addition of a bacterial superinfection against the background of immunosuppression (pneumonia, otitis media, encephalitis).
Laboratory diagnostics
Test material: blood, nasopharyngeal swabs, urine, feces, cerebrospinal fluid, conjunctival discharge.
- Serodiagnosis: ELISA with determination of IgM and IgG, complement fixation test, neutralization test, hemagglutination inhibition assay. The paired sera method is used (the second sample no earlier than 10 days after the first); a 4-fold increase in antibody titer is diagnostically significant. Blood is collected on days 4–5 from the appearance of the rash;
- Molecular diagnostics: PCR to detect viral RNA and determine the genotype (important for epidemiological surveillance). Material is taken on days 1–3 from the appearance of the rash — urine, nasopharyngeal swabs, cerebrospinal fluid;
- Virological method — isolation in cell cultures with registration of the cytopathic effect.
Treatment and Prevention
Etiotropic therapy is limited: immunomodulators and ribavirin are used. When a bacterial superinfection develops, antibiotics are prescribed strictly according to indications. Symptomatic treatment includes antipyretics (paracetamol, ibuprofen), as well as vitamin A for the prevention of ophthalmological complications associated with conjunctivitis.
Measles is a controlled infection. Specific prophylaxis is carried out with a live measles vaccine, including as part of the combined measles, mumps, and rubella (MMR) vaccine.
- Routine vaccination: first dose at 12 months, revaccination at 6 years;
- The minimum interval between doses during catch-up vaccination is 3 months;
- Emergency vaccination of contacts — within the first 72 hours from the identification of the patient;
- If there are contraindications to the vaccine, passive immunoprophylaxis with immunoglobulin is performed no later than the 5th day after contact.
Key points
- Measles virus is a Paramyxoviridae, genus Morbillivirus, an enveloped virus with a negative-sense RNA genome.
- Surface proteins H and F provide hemagglutination and cell fusion with the formation of symplasts; neuraminidase is absent.
- Anthroponotic disease with an airborne transmission mechanism and a 100% contagiousness index.
- Clinical triad: fever with intoxication, catarrhal syndrome with conjunctivitis, sequential maculopapular exanthem.
- Complications associated with transient immunosuppression and bacterial superinfection pose a significant danger.
- The primary diagnostic method is ELISA for IgM/IgG in paired sera; PCR is used for genotyping.
- Causal treatment includes ribavirin and immunomodulators; administration of vitamin A is mandatory.
- Prevention — live measles vaccine at 12 months and 6 years; emergency vaccination in the first 72 hours after contact.