measles

Measles is a highly contagious viral illness marked by a distinctive rash and systemic symptoms. It is caused by the Measles morbillivirus and spreads primarily through respiratory droplets. While often self-limiting, it can lead to severe complications, particularly in malnourished children or those with weakened immune systems. The disease is preventable through vaccination, which has drastically reduced its global incidence.

Signs and symptoms

The initial phase, known as the prodrome, lasts 2–4 days and features a high fever, often exceeding 104°F (40°C). This is accompanied by the "three Cs": cough, coryza (runny nose), and conjunctivitis. A pathognomonic sign is the presence of Koplik's spots, small white lesions on the buccal mucosa near the molars. The characteristic rash appears 3–5 days after symptoms begin, starting at the hairline and behind the ears before spreading downward. The rash consists of flat red spots that may blend together and is typically followed by a period of desquamation. Complications during this stage can include otitis media and laryngotracheobronchitis.

Cause and transmission

The causative agent is the Measles morbillivirus, a single-stranded, negative-sense RNA virus in the family Paramyxoviridae and genus Morbillivirus. It is closely related to viruses causing rinderpest and canine distemper. The virus is transmitted via airborne respiratory droplets expelled by infected individuals through coughing or sneezing. It can remain infectious in the air or on surfaces for up to two hours. The basic reproduction number (R₀) for measles is exceptionally high, estimated between 12 and 18, making it one of the most contagious human pathogens. Humans are the only natural reservoir for the virus.

Diagnosis and prevention

Diagnosis is typically clinical, based on the characteristic signs and symptoms, especially in an outbreak setting. Laboratory confirmation can be achieved through detection of IgM antibodies in serum or by reverse transcription polymerase chain reaction (RT-PCR) from a nasopharyngeal swab. The cornerstone of prevention is the measles vaccine, most commonly administered as part of the combined MMR vaccine or MMRV vaccine. The World Health Organization recommends two doses for effective immunity. Outbreak control relies on ring vaccination strategies and maintaining high population immunity, often above 95%, to achieve herd immunity. Post-exposure prophylaxis with the vaccine or immunoglobulin can be used for susceptible contacts.

Treatment and prognosis

There is no specific antiviral therapy; management is supportive and focuses on relieving symptoms and preventing complications. This includes bed rest, antipyretics like acetaminophen, hydration, and use of a humidifier. The World Health Organization recommends administration of high-dose vitamin A to all children diagnosed in areas with deficiency, as it can reduce severity and mortality. Treatment of secondary bacterial infections, such as pneumonia, requires appropriate antibiotics. The prognosis for most healthy, well-nourished individuals in developed countries is excellent. However, severe complications like encephalitis and subacute sclerosing panencephalitis (SSPE), a rare, fatal degenerative disease of the central nervous system, can occur years after initial infection.

Epidemiology and history

Before the introduction of the vaccine in 1963, major epidemics occurred every 2–3 years, causing an estimated 2.6 million deaths annually. The vaccine, developed by John Enders and colleagues, led to the declaration of measles elimination in the Americas in 2016. However, global eradication efforts have been hampered by inadequate health infrastructure, conflicts, and vaccine hesitancy, leading to significant resurgences. Major outbreaks have recently occurred in Samoa, the Democratic Republic of the Congo, and Ukraine. The disease remains a leading cause of vaccine-preventable death among children globally, with the highest burden in parts of Africa and Asia. The Global Vaccine Action Plan and initiatives like Gavi, the Vaccine Alliance continue to work toward increased immunization coverage.

Category:Viral diseases Category:Vaccine-preventable diseases Category:World Health Organization essential medicines