Measles is one of the most contagious viral infections affecting humans. The causative agent, measles virus (genus Morbillivirus, family Paramyxoviridae), is spread from human-to-human through air-borne respiratory droplets and direct contact with infected secretions. The disease is characterised by a prodromal stage of high grade fever, malaise, conjunctivitis, coryza and cough. One to two days before the onset of the characteristic morbilliform rash, multiple small whitish Koplik’s spots resembling grains of salt, a pathognomonic sign for measles, may be found on the buccal mucosa, just opposite to the first or second molar, and remain visible for 1-2 days after the appearance of skin rash. The incubation period for the measles is about 10-14 days. The infectious period of symptomatic cases starts from 4 days before through 4 days after the onset of the rash. Disease transmission from an asymptomatic exposed immune person has not been documented. As humans are the only natural hosts for the virus, measles is preventable and can be eliminated by vaccination. Without vaccination, approximately 95% of the population would have acquired measles infection by 15 years of age. In settings where there is reduced virus transmission among the younger population following rising vaccination coverage in the population, adolescents and young adults may become the most susceptible population group if they have not been exposed to wild-type measles virus or had no prior measles vaccination.

The severity, complication risk and clinical outcomes of measles virus infection varies greatly, depending on the person’s age, nutritional status and co-morbidities. The most common complications of measles are otitis media, pneumonia, croup, diarrhoea, post-infectious encephalitis and subacute sclerosing panencephalitis (SSPE). While young children are prone to develop severe life-threating pneumonia, either in the form of primary viral pneumonia or secondary bacterial pneumonia, adults aged >20 years are at risk of acute encephalitis. Measles infection in immunocompromised individuals, including the HIV infected, may have atypical presentation with no skin rash, and can be severe, prolonged and potentially fatal. Measles infection poses a special risk to susceptible females of reproductive age; it is associated with an increased risk of maternal, foetal, and neonatal complications. Infected pregnant women are at a higher risk of hospitalisation, foetal loss, premature labour, pneumonia and maternal death compared to infected non-pregnant women. Intrauterine measles virus infection may range from a mild illness including low birth weight to a severe, fatal outcome. Measles virus infection is not associated with teratogenicity.