Measles

Measles is an acute, highly contagious viral illness caused by the measles virus, a paramyxovirus spread by the respiratory route. It is characterised by fever, a cough-coryza-conjunctivitis prodrome, and a maculopapular rash, and it remains a leading vaccine-preventable cause of childhood illness where immunization coverage is incomplete (Moss, 2017).

Definition

Measles is an infection by the measles virus producing a systemic febrile illness with a distinctive prodrome and maculopapular rash, transmitted person-to-person through respiratory droplets and aerosols and preventable by live attenuated vaccine.

Scope

This topic covers measles as a clinical and public-health entity: its viral cause and transmission, the immune response it provokes, its characteristic course and major complications, and its epidemiology under vaccination. It is a reference overview and does not provide treatment protocols or individualised advice.

Core questions

• How is measles transmitted, and why is it so contagious?
• What is the typical clinical course and which complications are most important?
• How does measles infection affect the immune system beyond the acute illness?
• What level of population immunity is needed to interrupt transmission?

Key concepts

• Measles virus (Morbillivirus, Paramyxoviridae)
• Respiratory droplet and aerosol transmission
• Prodrome and Koplik spots
• Maculopapular rash
• Measles-induced immunosuppression
• Subacute sclerosing panencephalitis (SSPE)
• Live attenuated measles vaccine

Mechanisms

The measles virus enters via the respiratory tract, infects immune cells, and disseminates systemically before the rash appears. The host mounts a strong adaptive response that clears the virus and generally confers lifelong immunity, but the infection also suppresses immune function (Griffin, 2016; Griffin, 2010). This measles-induced immunosuppression can blunt responses to other pathogens for a period after the acute illness, contributing to secondary infections that account for much measles-associated morbidity and mortality. Rarely, persistent central-nervous-system infection leads to the late, progressive complication subacute sclerosing panencephalitis.

Clinical relevance

Understanding measles illustrates how a single highly transmissible virus can produce both an acute illness and a period of broader immune vulnerability, and why high vaccination coverage matters for population protection. This entry is descriptive and educational; it characterises the disease and its prevention and is not a basis for diagnosis or treatment in an individual patient.

Epidemiology

Measles is among the most contagious human infections, so very high population immunity is required to interrupt transmission. Vaccination drove large global declines in measles deaths, with modelling of surveillance data documenting substantial mortality reduction over the period to 2010 (Simons et al., 2012). Where coverage falls, measles resurges rapidly, and outbreaks continue to occur in undervaccinated communities (Moss, 2017).

History

Measles has been recognised as a distinct childhood illness for centuries, and its viral cause and route of spread were established in the twentieth century. The introduction of a live attenuated vaccine transformed its epidemiology, turning a near-universal childhood infection into a vaccine-preventable disease and making elimination an attainable goal in many regions (Moss, 2017).

Debates

How much does measles-induced immune suppression matter at the population level?

Beyond the acute illness, measles transiently impairs immunity to other pathogens; the magnitude and duration of this effect, and how much it contributes to wider mortality, are subjects of ongoing immunologic and epidemiologic study.

Key figures

• William J. Moss
• Diane E. Griffin

Seminal works

• moss-2017
• griffin-2016
• simons-2012

Frequently asked questions

Why is measles considered so contagious?

Measles virus spreads efficiently through respiratory droplets and aerosols, so a very high proportion of a population must be immune to interrupt transmission. This is why even small gaps in vaccination coverage can allow outbreaks.

What are the most serious complications of measles?

Important complications include pneumonia and, rarely, encephalitis and the late progressive condition subacute sclerosing panencephalitis. Measles also transiently suppresses immunity, increasing vulnerability to other infections after the acute illness.