Measles

Measles is a highly contagious, vaccine-preventable viral disease caused by the Measles morbillivirus, a member of the genus Morbillivirus within the family Paramyxoviridae. Historically known by several names, including morbilli, rubeola, nine-day measles, red measles, and English measles, it remains one of the most infectious human diseases. Symptoms typically develop around ten to twelve days after exposure and last approximately one week. Although often thought of as a childhood illness, measles can affect individuals of any age. Globally it continues to pose a significant public health burden, particularly in regions with low vaccination coverage.

Virology and Transmission

The measles virus is a single-stranded, non-segmented, enveloped RNA virus structurally and genetically related to rinderpest (eradicated in 2001) and canine distemper. Humans are the only natural host, and no known animal reservoirs exist.
Transmission occurs predominantly through airborne droplets expelled during coughing or sneezing. The virus can also spread via direct contact with respiratory secretions such as saliva or nasal mucus. Measles is exceptionally contagious: around nine out of ten susceptible individuals sharing living space with an infected person will contract the illness. People are infectious from four days before the onset of the rash to four days after its appearance.
The basic reproductive number (R₀) is one of the highest among known infectious diseases. While commonly cited as 12–18, some epidemiological analyses suggest a wider range across different population settings. High transmissibility underpins the necessity for widespread immunisation.

Signs and Symptoms

Measles manifests after an incubation period of approximately seven to fourteen days, most often around eleven to twelve days. An initial prodromal phase features:

• fever, often high and rising in a stepwise pattern
• malaise
• cough
• coryza (a profuse nasal cold)
• conjunctivitis

Small white lesions known as Koplik’s spots may appear on the buccal mucosa opposite the molars two to three days after the onset of symptoms. These are pathognomonic for measles but are transient and can be missed in clinical examination.
A characteristic maculopapular rash emerges three to five days after the prodrome, usually beginning on the face or behind the ears and spreading downwards across the body. The rash often deepens in colour before fading, a process sometimes described as staining. Conjunctivitis may cause photophobia, and systemic symptoms frequently peak around the time the rash appears. In uncomplicated cases, improvement typically begins within a few days of rash onset and disease resolution follows within seven to ten days.
Vaccinated individuals with partial immunity may develop modified measles, a milder form characterised by a prolonged incubation period, subtle symptoms, and a less prominent rash. Immunocompromised people may lack the typical rash or conjunctivitis, complicating diagnosis.

Complications

Complications from measles are common and may arise either directly from viral involvement or from immune suppression caused by the infection. Measles induces a phenomenon known as immune amnesia, whereby the virus depletes previously acquired immune memory. This can markedly increase vulnerability to other infections for several months to years after recovery.
Direct complications include:

• viral pneumonia
• acute encephalitis
• laryngotracheobronchitis (croup)
• corneal ulceration, which may lead to scarring and visual impairment
• the rare but fatal subacute sclerosing panencephalitis (SSPE), typically occurring years after infection

Secondary bacterial infections are frequent, such as:

• otitis media
• bacterial pneumonia
• infectious diarrhoea

High-risk groups include infants and young children under five years, adults over twenty, pregnant women, malnourished individuals, and people with compromised immune systems due to conditions such as HIV infection, leukaemia, or congenital immunodeficiency. Complications tend to be more severe in adults, and immunocompromised patients may face mortality rates approaching one-third in severe cases.
Long-term epidemiological studies prior to the introduction of routine vaccination suggest that immune suppression following measles infection can last two to three years, with significant reductions in antibody diversity against other pathogens.

Epidemiology and Global Impact

Measles remains endemic in many parts of the world. Although global vaccination efforts have led to dramatic reductions in morbidity and mortality, the disease still affects around twenty million people annually, particularly in parts of Africa and Asia where access to healthcare and vaccines remains limited.
Widespread vaccination programmes decreased global measles deaths by around 80 per cent between 2000 and 2017. By the mid-2010s, approximately 85 per cent of children worldwide had received at least one dose of measles-containing vaccine. Nevertheless, resurgence occurred in several regions between 2017 and 2019 due to declining immunisation coverage, sociopolitical instability, and vaccine hesitancy.
Historically, mortality from measles was substantial. In 1980, global deaths were estimated at around 2.6 million. By 1990, the annual death toll had fallen to roughly half a million, and by 2014 large-scale immunisation campaigns had reduced this figure to around 73,000. Despite these achievements, measles remains one of the leading causes of death from vaccine-preventable diseases worldwide.

Diagnosis

Diagnosis is typically based on clinical presentation in combination with epidemiological factors. Koplik’s spots, when present, offer strong diagnostic evidence, though laboratory confirmation is essential for public health surveillance and outbreak control.
Diagnostic techniques include:

• serology to detect measles-specific IgM antibodies
• polymerase chain reaction (PCR) testing to identify viral RNA in respiratory samples
• viral culture in specialised laboratories

Rapid identification allows health authorities to implement containment measures effectively.

Treatment and Supportive Care

There is no antiviral treatment that directly targets measles. Care is therefore supportive, aimed at relieving symptoms, preventing dehydration, and managing complications. Recommended measures include:

• oral rehydration solutions to replace fluids and electrolytes
• antipyretic medications
• adequate nutrition

Antibiotics are indicated only for confirmed secondary bacterial infections such as otitis media or pneumonia. Vitamin A supplementation is advised for all children under five diagnosed with measles, as it reduces the risk of severe complications, ocular damage, and mortality.
In industrialised countries, the overall case-fatality rate is low but not negligible. Deaths are most often associated with respiratory or neurological complications. In low-resource settings with high rates of malnutrition and limited healthcare access, fatality rates can be markedly higher.

Prevention and Vaccination

Vaccination is the most effective preventive measure. Measles vaccine, typically administered as part of the combined measles–mumps–rubella (MMR) vaccine, provides long-lasting immunity and is considered exceptionally safe.
Key points include:

• high coverage is essential; more than 95 per cent of a population must be immunised to achieve herd immunity
• two doses of the vaccine provide optimal protection
• vaccination campaigns have significantly reduced global incidence and mortality

Public health strategies emphasise maintaining high vaccination rates, rapid outbreak response, and robust surveillance systems to prevent re-establishment of endemic transmission.

Public Health Significance

Measles continues to serve as a major indicator of the strength of public health infrastructure due to its extreme transmissibility and the clarity with which lapses in immunisation lead to outbreaks. While the disease is entirely preventable through vaccination, global disparities in healthcare access, conflict, misinformation, and logistical challenges mean that measles control remains a central priority for international health organisations.