Measles is a highly contagious viral infection that primarily affects children. It is caused by the measles virus, a member of the Paramyxoviridae family. Despite the availability of an effective vaccine, measles remains a significant cause of morbidity and mortality worldwide, particularly in developing countries.
Measles is characterized by its distinctive rash and a constellation of symptoms including fever, cough, and conjunctivitis. The disease can lead to serious complications, especially in young children, immunocompromised individuals, and pregnant women. The World Health Organization (WHO) has targeted measles for global elimination, but outbreaks continue to occur even in countries with high vaccination rates.
Etiology of Measles Infection
Measles is caused by the measles virus, which has the following characteristics:
Single-stranded, negative-sense RNA virus
Member of the genus Morbillivirus in the Paramyxoviridae family
Enveloped virus, approximately 100-200 nm in diameter
Only one serotype, but multiple genotypes
Highly unstable in the environment, sensitive to heat and light
The virus is transmitted through respiratory droplets or direct contact with nasal or throat secretions of infected individuals. It can remain infectious in the air for up to two hours after an infected person leaves an area.
Epidemiology of Measles Infection
Measles epidemiology has changed dramatically since the introduction of widespread vaccination:
Before vaccination, major epidemics occurred every 2-3 years, primarily affecting children
Global measles deaths have decreased by 73% from 2000 to 2018 due to vaccination efforts
In 2018, there were an estimated 9.7 million cases and 142,000 deaths globally
Outbreaks still occur, even in countries with high vaccination coverage, often due to imported cases
Key epidemiological features:
Highly contagious: R0 of 12-18 (one infected person can infect 12-18 others in a susceptible population)
Seasonal pattern in temperate climates: peak incidence in late winter and early spring
Risk factors: unvaccinated status, malnutrition, vitamin A deficiency, immunocompromised state
Most vulnerable age group: children under 5 years old
Pathophysiology of Measles Infection
The pathophysiology of measles involves several stages:
Infection and Incubation:
Virus enters via respiratory route and infects epithelial cells
Spreads to local lymph nodes and replicates
Incubation period: 10-14 days
Prodromal Phase:
Viremia leads to infection of reticuloendothelial system
Fever, cough, coryza, and conjunctivitis develop
Koplik spots appear on buccal mucosa
Exanthem Phase:
Characteristic maculopapular rash appears
Rash is a result of T-cell mediated immunological response
Virus spreads to multiple organs
Recovery or Complications:
Immune response clears the virus in uncomplicated cases
Temporary immunosuppression for weeks to months after infection
Complications may arise due to viral replication or secondary bacterial infections
The measles virus also has a unique ability to infect and suppress immune cells, leading to prolonged immunosuppression after the acute illness.
Clinical Presentation of Measles Infection
The clinical course of measles typically progresses through three stages:
Prodromal Phase (2-4 days):
High fever (often >40°C or 104°F)
The "3 Cs": cough, coryza (runny nose), conjunctivitis
Koplik spots: pathognomonic white spots on buccal mucosa
Malaise, anorexia, diarrhea
Exanthematous Phase (5-6 days):
Characteristic maculopapular rash
Rash progression: starts behind ears and face, spreads downward to trunk and extremities
Rash initially red and blanching, later becoming confluent
Fever may spike higher as rash appears
Recovery Phase:
Rash fades in order of appearance, often leaving fine desquamation
Fever subsides
Cough may persist for 1-2 weeks
Atypical presentations can occur in immunocompromised patients or those with partial immunity, potentially leading to diagnostic challenges.
Diagnosis of Measles Infection
Diagnosis of measles involves clinical assessment and laboratory confirmation:
Clinical Diagnosis:
Based on characteristic symptoms and rash
Presence of Koplik spots is pathognomonic but not always observed
Laboratory Confirmation:
Serology: IgM antibodies in serum or saliva (detectable from day 3 of rash onset)
RT-PCR: Detection of viral RNA from respiratory specimens, urine, or blood
Virus isolation: Not routinely performed, mainly for research purposes
Other Investigations:
Complete blood count: Leukopenia with relative lymphocytosis
Chest X-ray: If respiratory complications are suspected
Differential diagnosis includes other viral exanthems such as rubella, roseola, and scarlet fever. In countries with low measles incidence, laboratory confirmation is crucial for all suspected cases.
Treatment of Measles Infection
There is no specific antiviral treatment for measles. Management is primarily supportive and focuses on preventing complications:
Supportive Care:
Rest and adequate hydration
Antipyretics for fever (avoid aspirin in children due to Reye's syndrome risk)
Nutritional support
Vitamin A Supplementation:
WHO recommends vitamin A for all children with measles
Dosage varies by age: 50,000 IU for infants <6 months, 100,000 IU for 6-11 months, 200,000 IU for ≥12 months
Two doses given 24 hours apart; a third dose 2-4 weeks later if clinical signs of vitamin A deficiency
Management of Complications:
Antibiotics for secondary bacterial infections (e.g., pneumonia, otitis media)
Airway management and oxygen therapy if needed
Intensive care for severe complications
Isolation Precautions:
Airborne precautions in healthcare settings
Isolation at home until 4 days after rash onset
Post-exposure prophylaxis with measles vaccine or immunoglobulin may be considered for unvaccinated contacts, depending on the timing of exposure and the individual's risk factors.
Prevention of Measles Infection
Prevention of measles relies primarily on vaccination:
Vaccination:
MMR (Measles, Mumps, Rubella) vaccine: Live attenuated vaccine
Recommended schedule: First dose at 12-15 months, second dose at 4-6 years
Two doses provide 97% protection against measles
Catch-up Vaccination:
Unvaccinated children, adolescents, and adults should receive two doses at least 28 days apart
Important for healthcare workers and international travelers
Outbreak Control:
Rapid identification and isolation of cases
Contact tracing and post-exposure prophylaxis
Supplementary immunization activities in affected communities
Global Elimination Efforts:
WHO's Global Vaccine Action Plan aims for measles elimination in at least five WHO regions by 2020
Strengthening routine immunization programs
Surveillance and rapid response to outbreaks
Maintaining high vaccination coverage (>95%) is crucial for herd immunity and preventing outbreaks. Public health education about the importance of vaccination is an ongoing challenge in many regions.
Complications of Measles Infection
Measles can lead to various complications, particularly in young children, malnourished individuals, and those with compromised immune systems:
Respiratory Complications:
Pneumonia (viral or secondary bacterial): Most common cause of measles-related deaths
Laryngotracheobronchitis (croup)
Otitis media
Neurological Complications:
Acute encephalitis (1 in 1000 cases)
Subacute sclerosing panencephalitis (SSPE↗️): Rare but fatal late complication
Febrile seizures
Gastrointestinal Complications:
Diarrhea and dehydration
Hepatitis
Appendicitis (rare)
Hematological Complications:
Thrombocytopenia
Disseminated intravascular coagulation (rare)
Ocular Complications:
Keratitis
Blindness (due to vitamin A deficiency)
Other Complications:
Myocarditis
Severe malnutrition in developing countries
Pregnancy complications: Increased risk of premature labor, low birth weight, and maternal death
The risk of complications is highest in children under 5 years of age, adults over 20 years, pregnant women, and immunocompromised individuals. Prompt recognition and management of complications are crucial for reducing morbidity and mortality associated with measles.
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Nonpurulent conjunctivitis and facial rash of measles one day after rash began.(source)
Measles: Objective QnA
What is the causative agent of measles?
Measles virus (Paramyxovirus family)
What is the primary mode of transmission for measles?
Airborne respiratory droplets
What is the incubation period for measles?
7-14 days (average 10-12 days)
What are the characteristic symptoms of the prodromal phase of measles?
Fever, cough, coryza (runny nose), and conjunctivitis (3 C's)
What is the name of the pathognomonic enanthem seen in measles?
Koplik spots
Where are Koplik spots typically found?
Buccal mucosa opposite the lower molars
What is the characteristic rash of measles called?
Maculopapular rash
In what order does the measles rash typically spread?
Head to trunk to extremities
How long does the measles rash usually last?
5-7 days
What is the most common complication of measles in children?
Otitis media
What is the most serious respiratory complication of measles?
Pneumonia
What is the most severe neurological complication of measles?
Acute encephalitis
What is the rare but fatal late complication of measles that can occur years after infection?
Subacute sclerosing panencephalitis (SSPE)
What vitamin deficiency is associated with increased severity of measles?
Vitamin A deficiency
How long is a person with measles considered infectious?
From 4 days before to 4 days after rash onset
What is the recommended age for the first dose of the MMR vaccine?
12-15 months
When is the second dose of the MMR vaccine typically given?
4-6 years of age
What is the efficacy of two doses of the MMR vaccine in preventing measles?
97-99%
Can measles infection occur in vaccinated individuals?
Yes, but it's rare and usually milder (breakthrough infection)
What is the R0 (basic reproduction number) of measles?
12-18, one of the most contagious viruses known
What percentage of susceptible household contacts typically develop measles after exposure?
90%
What is the typical duration of immunity after natural measles infection?
Lifelong
What type of genetic material does the measles virus contain?
Single-stranded negative-sense RNA
Which cells does the measles virus primarily infect?
Lymphocytes and epithelial cells
What is the name of the receptor the measles virus uses to enter cells?
CD150 (SLAM) receptor
What is the approximate size of a measles virus particle?
100-300 nanometers
What is the global vaccination coverage for the first dose of measles-containing vaccine?
Approximately 85% (as of 2021)
What is the most common cause of death in measles cases?
Pneumonia
Can measles infection during pregnancy affect the fetus?
Yes, it can lead to miscarriage, stillbirth, or preterm birth
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