What are measles?

Causes and Symptoms

Measles is a highly contagious viral disease characterized by a maculopapular (pimply) rash that develops on the skin and spreads rapidly over much of the cutaneous surface of the body. Measles virus is classified with the paramyxoviruses, a class of viruses in which ribonucleic acid (RNA) serves as the genetic material. Closely related viruses in the same group include rinderpest and distemper virus, agents associated with disease in ruminants such as cows and in dogs or cats, respectively. It is likely that measles originated when one of these other animal viruses became adapted to humans several thousand years ago.

In modern times but before the advent of measles vaccination, measles was a common disease of childhood, usually appearing between the ages of five and ten. The illness is among the most contagious of infections, and the virus was generally spread among children in schools. Widespread immunization of children, begun in the 1960s, tended to push the age of exposure into the teenage years. Most outbreaks since the 1980s have occurred among college students. Since recovery from the disease confers lifelong immunity, infection among older adults is infrequent. In developing nations, places where vaccination may be haphazard, measles is still a disease of early childhood; malnutrition and related problems of poverty have resulted in a significant level of mortality among infected children.

Exposure generally follows an oral-oral means of transmission, as the person inhales contaminated droplets from an infected individual. The incubation period for active measles ranges from seven to fourteen days. During this early stage, the infected individual becomes increasingly contagious. The lack of any obvious symptoms during these early stages lends itself to the spread of the disease.

Contact by the virus with the surface cells of the respiratory passages, or sometimes the conjunctiva (the outer surface of the eye), allows the infectious agent to enter the body. The virus spreads through the local lymph nodes into the blood, producing a primary viremia. During this period, the virus replicates both in the lymph nodes and in the respiratory sites through which the virus entered the body. The virus returns to the bloodstream, resulting in a secondary viremia and widespread passage of the virus throughout the body by the fifth to seventh day after the initial exposure. Viral levels in the blood reach their peak toward the end of the incubation period, some fourteen days after infection. Once symptoms begin, the virus is widely disseminated throughout the body, including sites in small blood vessels, lymph nodes, and even the central nervous system.

The initial incubation period is followed by a prodromal stage, in which active symptoms appear. This stage is characterized by a fever that may reach as high as 103 degrees Fahrenheit, coughing, sensitivity of the eyes to light (photophobia), and malaise. Koplik’s spots appear on the buccal mucosa in the mouth one to two days prior to development of the characteristic measles rash.

The maculopapular rash first appears on the head and behind the ears and gradually spreads over the rest of the body during the course of twenty-four to forty-eight hours. Clear signs of respiratory infection appear, including a cough, pharyngitis, and occasional involvement of the bronchioles or even pneumonia. While malaise and anorexia (appetite loss) are common during the fever period, diarrhea and vomiting generally do not occur. Over time, the rash becomes increasingly dense, exhibiting a blotchy character. Desquamation is common in many affected areas of the skin. Gradually, over a period of three to five days, the rash begins to fade, usually following the sequence by which it first appeared. The rash fades first on the forehead, then on the extremities.

Complications, while they do occur, are unusual in otherwise healthy individuals. Most result from secondary bacterial infections. Occasionally, these complications may manifest themselves as infections of the ear. Pulmonary infections are common among cases of measles and account for most of the rare deaths that follow development of the disease. Photophobia is also common, accounting for the former belief that measles patients had to be kept in a dark room; as long as the patient is comfortable, this step is unnecessary.

The obvious manifestations of measles infection make the isolation of the virus unnecessary for diagnosis. Ironically, the near disappearance of measles in the United States has made most physicians there unfamiliar with the disease; it is not unusual for an attending physician to mistake the rash for another illness. For this reason, laboratory diagnosis is often useful. Laboratory confirmation is generally based on a serological assay for measles antibodies in the blood of infected persons.

A rare sequela to measles infection is the development of subacute sclerosing panencephalitis, a disease characterized by progressive neurological deterioration. The specific mechanism by which measles infection may develop into this disease remains unclear, but it may be the result of a rare combination of events in the victim. Since spread of the virus into the central nervous system is common during measles infection whereas the development of subacute sclerosing panencephalitis is rare (approximately one case per one hundred thousand measles infections), it is likely that some form of immune impairment is at the root of this disease. Diagnosis of subacute sclerosing panencephalitis is difficult and is based on developing dementia accompanied by unusual levels of measles antibodies in cerebrospinal fluid.

Treatment and Therapy

No specific treatment for measles is available; therapy consists of symptomatic intervention. Bed rest is recommended, and the patient should not come into contact with persons not previously exposed to the virus through either natural infection or immunization.

Itching of the rash is common and may be treated with cool water or the standard regimen of cornstarch or baking soda applications. The most common complications result from secondary bacterial infections, which generally take the form of otitis media (middle-ear infection), pharyngitis, or pneumonia. Appropriate use of antibiotics is usually sufficient to prevent or treat such complications.

Immunization with the measles virus may be either passive or active. Children less than one year of age and patients who are immunocompromised or chronically ill may be protected if human immunoglobulin is administered within a week after exposure. While effective immunity is short term, it is capable of protecting these individuals during this period. Since no active disease or infection develops, however, immunity to future infection remains minimal in these cases.

During the early 1960s, an effective
vaccine was developed to immunize children against measles. The vaccine consists of an attenuated form of the virus. Although early forms of the vaccine were inconsistent in producing a lifelong immunity, they were effective in decreasing the prevalence of the disease. Later generations of the attenuated vaccine proved more effective in developing long-term immunity among the recipients.

Since maternal antibodies are present in newborns, it is recommended that measles immunization begin between twelve and fifteen months of age. Often, this program is part of a combination MMR vaccine, for measles, mumps, and rubella (German measles). A second booster is given following elementary school. The American Academy of Pediatrics does not consider a third vaccination to be necessary if the approved routine has been followed. It is recommended that children who were first immunized prior to their first birthday should receive boosters at fifteen months of age and again at age twelve. Indications are that immunity from vaccination is long term, if not lifelong. Recovery from natural infection results in a lifelong immunity to measles.

Inconsistency of the first generation of vaccine resulted in ineffective immunity among some individuals vaccinated during the 1960s. A number of small outbreaks during the 1980s were the result. Most cases of measles, however, have occurred in individuals who failed to be immunized.

Perspective and Prospects

The origin and early history of measles is uncertain, as the first authentic description of measles as a specific entity was that by the Arab physician al-Razi (Rhazes) in a 910 CE treatise on smallpox and measles. Rhazes quoted earlier work by the Hebrew physician El Yehudi, so it is likely that familiarity with these respective illnesses had existed for some time.

Measles is entirely a human disease, with no known animal reservoir. Consequently, the paucity of human populations of sufficient size to maintain transmission means that the spread of such an epidemic disease would have been unlikely before 2500 BCE. It is probable that the disease entered the human species through adaptation of the similar animal viruses of rinderpest or distemper. The absence of any description of a disease like measles in the writings of Hippocrates (c. fourth century BCE) likewise renders it unlikely that the disease was widespread before that date.

Epidemic disease with a rash characteristic of measles is known to have spread through the Roman Empire during the early centuries of the common era. The difficulty in differentiating measles from smallpox by the physicians of the time contributes to the difficulty in understanding the history of the illness. It is certain that by the time of Rhazes, measles had become common in the population.

The terminology of measles lent further confusion during the Middle Ages. Measles was often referred to as morbilli, a Latin term meaning “little disease,” to distinguish it from il morbo, or plague. The word measles first appeared in the fourteenth century treatise Rosa Anglica, by John of Gaddesden. The term may have been applied initially to the sores on the legs of lepers (mesles), and it was only later that illnesses characterized by similar rashes (measles, smallpox, and rubella) were clearly differentiated by European physicians. The significance of a rash with a white center in the mouth was probably recognized by John Quier in Jamaica and Richard Hazeltine in New England during the latter portion of the eighteenth century, but it was in 1896 that the American pediatrician Henry Koplik firmly reported its role in early stages of the disease.

Measles followed the path of European explorers to the Americas during the sixteenth century. Repeated outbreaks of measles devastated American Indian populations, which had minimal immunity to the newly introduced disease. The most thorough epidemiological investigation of measles newly introduced into a population was that by Peter Panum in his study Observations Made During the Epidemic of Measles on the Faroe Islands in the Year 1846 (1940). In the population of 7,864 persons, 6,100 became ill, with 102 deaths. Mortality rates as high as 25 percent were not unusual in previously unexposed populations. In Hawaii in 1848, about 40,000 deaths occurred among the population of 150,000 persons following the introduction of measles. Even higher mortality rates probably occurred among the populations of Peru and Mexico in 1530–31, following their exposure to infected Spanish explorers.

The earliest attempt at immunization was probably that of Francis Home of Edinburgh in 1758. Home soaked cotton in the blood of measles patients and placed it on the small cuts on the skin of children. The viral nature of measles was first demonstrated by John Anderson and Joseph Goldberger of the United States Public Health Service, who in 1911 induced the disease in monkeys using filtered extracts from human tissue. In 1954, the virus itself was isolated by John Enders, who grew the agent in human and monkey tissue in a laboratory.

The first effective vaccine was developed by Enders in 1958 using an attenuated (live) form of the virus. The vaccine was tested and then licensed in 1963. Several variations of the vaccine that proved superior in producing long-term immunity were developed in the decades that followed. In 1974, the World Health Organization (WHO) introduced a widespread vaccination program within developing countries.

The absence of any natural reservoir for measles other than humans has made the eradication of the disease possible. Active immunization of children in the United States reduced the annual incidence of the disease from 482,000 reported cases in 1962 to fewer than 1,000 in the late 1990s. The Measles and Rubella Initiative, a collaboration between the WHO, UNICEF, American Red Cross, US Centers for Disease Control and Prevention (CDC), and UN Foundation, has vaccinated one billion children worldwide since 2000. While widespread vaccination and worldwide surveillance has made global eradication of the disease a realistic possibility, the WHO reports that more than twenty million people contract measles each year and that it remains one of the top killers of children around the world, causing 145,700 deaths in 2013. Most of these fatalities occurred in children younger than five.

Outbreaks in 2014 and 2015

Though the CDC reports that measles was declared eliminated (no longer endemic or constantly present) in the United States as of 2000 becuase of access to effective vaccination, a record number of cases were reported in 2014. Of the 644 cases that occurred throughout twenty-seven states that year, the CDC stated that the majority of people who suffered from the infection were unvaccinated; the incident was linked to travelers coming to the country from the Philippines, which had recently suffered an outbreak. At the beginning of the following year, yet more measles outbreaks were highly publicized. From January to the end of February, the CDC confirmed that 170 people from seventeen states had measles. Most of these cases were considered part of an ongoing outbreak that experts believed began when an infected traveler visited a California amusement park. Aside from this outbreak, three other unrelated outbreaks were reported in Illinois, Nevada, and Washington state. The CDC issued an official Health Advisory in January to inform health care providers about the incidents and the ongoing investigations. At the state level, by the beginning of March lawmakers in several states started pushing for stricter regulations regarding nonmedical exemptions for vaccination; the surgeon general stressed the importance of vaccinating children.

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