Measles is caused by an RNA virus called measles virus (MV) belonging to the family Paramyxoviridae.
Route of spread
Measles is highly infectious with a high secondary infection rate in contacts, especially household contacts. The infection is spread by the respiratory droplet route.
Measles has a worldwide prevalence with most infections occurring in childhood. In the Western world infection below the age of one year is unusual, due to protection offered by maternal antibody. In the developing world, however, due to poor acquisition of maternal antibody, measles under one year is common and has a high mortality rate because of secondary bacterial infection and poor nourishment.
Measles was endemic in the UK with epidemics occurring every 2–3 years prior to the introduction of the childhood measles, mumps and rubella (MMR) vaccination programme in the mid 1980s. However, outbreak clusters have occurred recently because of the fall in the uptake of measles vaccination. Humans are the only host, and the World Health Organization estimates that worldwide there are over a million childhood deaths due to measles each year, and have declared measles as one of the infections to be eradicated from the world.
10–15 days, an average of two weeks.
Prodromal period (2–3 days before the rash appears) to about 4 days after the rash appears.
People at risk
All susceptible individuals, but especially those who are immunocompromised or pregnant.
The typical measles rash is preceded by a 2–3 day prodromal illness, which consists of cough, fever (38_C and above), conjunctivitis and rhinitis. At this stage, typical white lesions called Koplik’s spots can be seen in the inside of cheek buccal mucosa in a proportion of cases; these are diagnostic of measles. Patients are highly infectious in the prodromal stage and the virus is shed and spread from respiratory secretions. The prodromal stage is followed by the appearance of a maculopapular rash, which first appears on the face and neck and then spreads to the trunk and limbs. The rash and fever fade by 4–5 days.
Secondary bacterial infection
Causing otitis media, laryngotracheitis, broncho-pneumonia. These are common in children with measles in developing countries due to poor nourishment, and the cause of high measles mortality rates there.
- Acute post-infectious measles encephalitis: This typically occurs about a week or 10 days after the rash disappears. It is accompanied by headache, irritability, loss of consciousness and fever. This is due to demyelination as a result of auto-immune reaction to the measles virus and therefore the virus cannot be found in the central nervous system. It is relatively uncommon (1 in 1000 cases of measles) and has a high mortality rate.
- Subacute sclerosing pan-encephalitis (SSPE): This is a rare condition with an incidence of 1 in a million measles cases, but is invariably fatal. Typically symptoms appear several years (10–15 years) after the initial acute attack of measles in early childhood. The first signs are deterioration in intellect (poor performance at school) followed by motor dysfunction and seizures. A defect in the measles virus allows it to persist in the brain by ‘hiding’ from the immune system. Virus can therefore be found in the brain and cerebro-spinal fluid (CSF) in SSPE by molecular techniques and this confirms the diagnosis.
Such patients do not develop a rash at all or may have an atypical measles rash. Measles pneumonitis called giant cell pneumonitis is common, and may be present without ameasles rash. Diagnosis can be confirmed by detecting the virus in respiratory secretions. Measles pneumonitis has a high mortality rate.
There is no effective treatment for measles. Anecdotally, ribavirin has been used to treat measles pneumonitis in the immunocompromised and SSPE, but is of doubtful efficacy.
Live attenuated measles vaccine as triple vaccine with mumps and rubella (MMR) is recommended at 13–15 months (to allow maternal antibody to disappear as otherwise it may interfere with vaccine take) with a pre school booster. High levels of vaccine coverage (approximately 90%) are required for interruption of spread, and due to the falling uptake in MMR as a result of bad publicity over the past decade several localized outbreaks of measles have occurred in the UK recently.
There is no evidence that MMR vaccine is associated with autism and it is regarded as a safe and effective vaccine.
The MMR vaccine can be given within 72 hours of exposure as post-exposure prophylaxis. Normal immunoglobulin should be given as post-exposure prophylaxis to those at risk in whom MMR is contraindicated (e.g. pregnant and immunocompromised patients) or those who present within 6 days of at-risk exposure.
Measles is one of the most highly contagious infections with attack rates of >80% in household contacts. As it is spread by the respiratory route, respiratory precautions should be instituted for those at risk. The infection is spread via small droplets, which are released in the environment while sneezing, coughing etc. These droplets containing the infectious virus may either be inhaled or be inoculated into respiratory mucous membrane via contaminated hands or fomites such as handkerchiefs.
Susceptible healthcare workers (HCWs) who work with at-risk patients should be excluded from work during the incubation period if exposed to measles. All infected HCWs should be excluded from work during the infectious period.