The can then help hide the virus from

The measles virus, which had become extremely uncommon in developed countries, is making a comeback. It is a very contagious virus. This lesson will discuss the proteins involved in helping the measles virus complete its life cycle.

Measles

Measles is a childhood infection caused by the highly infectious measles virus.

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The illness begins with fever, runny nose, and a cough. A few days later, a characteristic rash begins to form all along the body, and the fever may reach a high of 104° Fahrenheit. Ear infections are a common problem for measles patients, and left untreated, can lead to hearing loss.

While most cases of measles are mild, resulting in itching and discomfort, it can cause serious problems, such as pneumonia and encephalitis (swelling of the brain).Thanks to an effective vaccine, measles is no longer as prevalent as it once was. However, due to a lack of vaccination in the past few years, there have been some recent worldwide measles outbreaks. In 2013, nearly 150,000 children died from the easily-preventable infection.

Because measles only infects humans, it is a great candidate for elimination — if vaccine compliance is high enough.

Measles Virus Structure

The measles virus belongs to the paramyxoviridae family. It is round, like a ball, and has an envelope on the outside. When it leaves the host cell, the measles virus steals part of the cell’s membrane to make the envelope, which can then help hide the virus from the host’s immune system. Underneath the envelope is the matrix, made from a protein called M. The matrix acts as glue to connect the envelope to the inside of the virus.

The viral genome is covered by a nucleocapsid protein called N. Two other proteins in the virus are the large protein called L, and the phosphoprotein called P. Both of these are involved with making new copies of the measles virus. They help copy the genome and make new viral proteins.

Electron micrograph of measles virus.

Measles Virus

Measles Virus Replication

Measles virus has two proteins, called H and F, sticking out from its envelope that help it enter a host cell. These proteins help the virus attach to the outside of the cell. The virus then fuses its envelope with the host cell membrane to get inside. To imagine this, picture two bubbles fusing together to become one larger bubble (just remember that the virus will be much smaller than the host cell).

Like all viruses in the paramyxoviridae family, the measles virus has a single-stranded, negative sense RNA genome. This means that its genetic information is stored as RNA. When the virus enters a host cell, the P and L proteins will make a strand of RNA that is complimentary to the genomic strand. This strand will then be used as instructions for both making viral proteins and as a template to make more of the original genome.

Again, this will be carried out by the P and L proteins.After enough viral proteins and genomes have been made, it’s time for the newly formed viral particles to go out and infect new host cells. The viral particles will simply ‘bud off’ from the host cell membrane. This is pretty much the opposite of the entry process. It is during this budding off process that the virus will steal its envelope from the host cell membrane.

Lesson Summary

Measles is a highly contagious member of the paramyxoviridae family. While most infections are mild, serious complications are possible.

The virus has an envelope covering a matrix and nucleocapsid structure. The nucleocapsid houses the single-stranded RNA genome. Various viral proteins help replicate the viral RNA and make proteins within a host cell so that new viruses can go out and continue the infection cycle.

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