Measles

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Measles virus
Measles virus
Virus classification
Group: Group V ((-)ssRNA) Order: Mononegavirales Family: Paramyxoviridae Genus: Morbillivirus Species: Measles virus

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Measles is a disease caused by the Morbillivirus. It is transmitted into the respiratory by contact with infected fluids. Incubation lasts for 4-12 days, during which patients are asymptomatic. Symptomatic onset includes the appearance of a distinct rash. Infected people remain contagious until appearance of the first symptoms until 3-5 days after the rash appearance.

Background

Measles, also known as rubeola, is a disease caused by a virus , specifically a paramyxovirus of the genus Morbillivirus.

Reports of measles go as far back to at least 600 B.C. however, the first scientific description of the disease and its distinction from smallpox is attributed to the Persian physician Ibn Razi (Rhazes) 860-932 who published a book entitled "Smallpox and Measles" (in Arabic: Kitab fi al-jadari wa-al-hasbah). In 1954, the virus causing the disease was isolated from an 11-year old boy from the US, David Edmonston, and adapted and propagated on chick embryo tissue culture. To date, 21 strains of the measles virus have been identified. Licensed vaccines to prevent the disease became available in 1963.

Measles is spread through respiration (contact with fluids from an infected person's nose and mouth, either directly or through aerosol transmission), and is highly contagious—90% of people without immunity sharing a house with an infected person will catch it. Airborne precautions should be taken for all suspected cases of measles.

The incubation period usually lasts for 4–12 days (during which there are no symptoms).

Infected people remain contagious from the appearance of the first symptoms until 3–5 days after the rash appears.

German measles is an unrelated condition caused by the rubella virus.

Symptoms

The classical symptoms of measles include a fever for at least three days, and the three Cs—cough, coryza (runny nose) and conjunctivitis (red eyes). The fever may reach up to 104° Fahrenheit/ 40° Celsius. Koplik's spots seen inside the mouth are pathognomonic (diagnostic) for measles but are not often seen, even in real cases of measles, because they are transient and may disappear within a day of arising.

The characteristic measles rash is classically described as a generalized, maculopapular, erythematous rash that begins several days after the fever starts. It starts on the head before spreading to cover most of the body, often causing itching. The rash is said to "stain", changing colour from red to dark brown, before disappearing.

Diagnosis and treatment

Clinical diagnosis of measles requires a history of fever of at least three days together with at least one of the three Cs. Observation of Koplik's spots is also diagnostic of measles.

Alternatively, laboratory diagnosis of measles can be done with confirmation of positive measles IgM antibodies or isolation of measles virus RNA from respiratory specimens. In cases of measles infection following secondary vaccine failure IgM antibody may not be present. In these cases serological confirmation may be made by showing IgG antibody rises by Enzyme immunoasay or complement fixation.

Positive contact with other patients known to have measles adds strong epidemiological evidence to the diagnosis.

There is no specific treatment or antiviral therapy for uncomplicated measles. Most patients with uncomplicated measles will recover with rest and supportive treatment.

Some patients will develop pneumonia as a sequela to the measles. Histologically, a unique cell can be found in the paracortical region of hyperplastic lymph nodes in patients affected with this condition. This cell, known as the Warthin-Finkeldey cell, is a multinucleated giant with eosinophilic cytoplasmic and nuclear inclusions.

Virology

Measles virus (MV) is an enveloped, nonsegmented negative-stranded RNA virus of the Paramyxoviridae family.

Transmission

The measles is a highly contagious airborne pathogen which spreads primarily via the respiratory system. The virus is transmitted in respiratory secretions, and can be passed from person to person via aerosol droplets containing virus particles, such as those produced by a coughing patient. Once transmission occurs, the virus infects the epithelial cells of its new host, and may also replicate in the urinary tract, lymphatic system, conjunctivae, blood vessels, and central nervous system.

Humans are the only known natural hosts of measles, although the virus can infect some non-human primate species.

Complications

Complications with measles are relatively common, ranging from relatively mild and less serious diarrhea, to pneumonia and encephalitis (subacute sclerosing panencephalitis). Complications are usually more severe amongst adults who catch the virus.

The fatality rate from measles for otherwise healthy people in developed countries is low: approximately 1 death per thousand cases. In underdeveloped nations with high rates of malnutrition and poor healthcare, fatality rates of 10 percent are common. In immunocompromised patients, the fatality rate is approximately 30 percent.

Public health

A scene from 1949's Polka-Dot Puss, where Tom and Jerry are put in quarantine after getting the measles. The disease was common during the time when the cartoon was made.

Measles is a significant infectious disease because, while the rate of complications is not high, the disease itself is so infectious that the sheer number of people who would suffer complications in an outbreak amongst non-immune people would quickly overwhelm available hospital resources. If vaccination rates fall, the number of non-immune persons in the community rises, and the risk of an outbreak of measles consequently rises.

In developed countries, most children are immunized against measles at the age of 18 months, generally as part of a three-part MMR vaccine (measles, mumps, and rubella). The vaccination is generally not given earlier than this because children younger than 18 months usually retain anti-measles immunoglobulins (antibodies) transmitted from the mother during pregnancy. A "booster" vaccine is then given between the ages of four and five. Vaccination rates have been high enough to make measles relatively uncommon. Even a single case in a college dormitory or similar setting is often met with a local vaccination program, in case any of the people exposed are not already immune. In developing countries, measles remains common.

Unvaccinated populations are at risk for the disease. After vaccination rates dropped in northern Nigeria in the early 2000s due to religious and political objections, the number of cases rose significantly, and hundreds of children died. A 2005 measles outbreak in Indiana was attributed to children whose parents refused vaccination. In the early 2000s the MMR vaccine controversy in the United Kingdom regarding a potential link between the combined MMR vaccine (vaccinating children from mumps, measles and rubella) and autism prompted a comeback in the measles party, where parents deliberately infect the child with measles to build up the child's immunity without an injection. This practice poses many health risks to the child, and has been discouraged by the public health authorities. Scientific evidence provides no support for the hypothesis that MMR plays a role in causing autism. Declining immunisation rates in the UK are the probable cause of a significant increase of cases of measles, 2006 being the highest on record, and 2007 already showing an increase on the previous year.

According to the World Health Organization (WHO), measles is a leading cause of vaccine preventable childhood mortality. Worldwide, the fatality rate has been significantly reduced by partners in the Measles Initiative: the American Red Cross, the United States Centers for Disease Control and Prevention (CDC), the United Nations Foundation, UNICEF and the World Health Organization (WHO). Globally, measles deaths are down 60 percent, from an estimated 873,000 deaths in 1999 to 345,000 in 2005. Africa has seen the most success, with annual measles deaths falling by 75 percent in just 5 years, from an estimated 506,000 to 126,000.

The joint press release by members of the Measles Initiative brings to light another benefit of the fight against measles: "Measles vaccination campaigns are contributing to the reduction of child deaths from other causes. They have become a channel for the delivery of other life-saving interventions, such as bed nets to protect against malaria, de-worming medicine and vitamin A supplements. Combining measles immunization with other health interventions is a contribution to the achievement of Millennium Development Goal Number 4: a two-thirds reduction in child deaths between 1990 and 2015."

Worldwide MMR Eradication

(Not to be confused with the World Health Organization's Measles Initiative)

Most recently, in 2007, the country Japan has become a nidus for the Measles. Japan has suffered a record number of cases, and a number of universities and other institutions in the country have closed in an attempt to contain the outbreak.[2]

In the 1990s, the governments of the Americas, along with the Pan American Health Organization, launched a plan to eradicate Measles, Mumps, and Rubella from the region.

Indigenous measles has been eliminated in North, Central, and South America; the last endemic case in the region was reported on November 12, 2002. [3]

Outbreaks are still occurring, however, following importations of measles viruses from other world regions. For example, in June 2006, there was an outbreak in Boston which resulted from a resident who had recently visited India. In 2005, there was an outbreak in a non-immunized population in Indiana and Illinois, transmitted by an Indiana girl who visited Romania without being vaccinated. There are also plans underway to eliminate Rubella from the region by 2010 [4]. As of 2006, endemic cases were still being reported in Bolivia, Brazil, Colombia, Guatemala, Mexico, Peru, and Venezuela, they are currently vaccinating Dominican Republic.

While some smaller organizations have proposed a global MMR eradication [5], none is likely to take place until, at least, after the worldwide eradication of Poliomyelitis.

External links

• WHO.int - 'Initiative for Vaccine Research (IVR): Measles', World Health Organization (WHO)
• Measles FAQ from Centers for Disease Control and Prevention in the United States