This lesson discusses the structure and function of the virus that causes mumps. Following the lesson there will be quiz questions so that you can see how much you have learned.
Mumps Virus Definition
Mumps was a common childhood disease before a vaccination became available for the virus. When people think of mumps, they often think of swollen cheeks due to the swelling of the salivary glands located next to the ears. However, because of the types of tissues that the mumps virus can infect, complications such as encephalitis, meningitis, swelling of the ovaries, and swelling of the testes can occur.
Before the vaccination was introduced, mumps was the most common cause of acquired deafness in children. This lesson will cover the structure of the mumps virus and how the virus leads to disease.
Mumps Virus Structure
A virus consists of small and simple particles that are capable of taking over cells and making them do what they want. Viruses enter a cell with a few simple genes and are able to take over the cell’s metabolism and ability to protect itself. This portion of the lesson will describe the features of the mumps virus that allow it to invade and hijack cells in the human body.
Let’s first look at the envelope of the virus. The envelope of the mumps virus is a lipid bilayer, similar to the cell membrane that surrounds human cells. In fact, the lipids found in the viral envelop are derived from the host cell. Viral proteins, associated with the envelope discussed next, are essential for viral replication.
F-protein, depicted as red triangles in this figure, allows the viral nucleocapsid to break into susceptible areas by fusing with the cell membrane.HN, or attachment protein, depicted in orange in the figure, is important in allowing the virus to attach to host cells. If the virus can’t attach to the host cell, it can’t fuse with the cell membrane and enter the cell.
The attachment protein of the mumps virus is hemagglutinin-neuraminidase glycoproteins (protein with a sugar added); other viruses in the same virus family (paramyxoviridae) as mumps have other glycoproteins on their membranes.The M, or matrix protein, shown in green in the figure, associates with the nucleocapsid and makes sure that all the viral components are assembled correctly before leaving the cell. The M protein attaches and forms an area on the plasma membrane where other viral components can be attached and packaged.
Now let’s look at the nucleocapsid and its structures.The capsid is a structure made of repeating protein subunits called nucleoprotein (or NP) that protects the viral genome and aids in replication inside the host cell. The capsid and the genome together are called the nucleocapsid.The genome of the mumps virus is a negative-sense single-stranded RNA, or a negative-sense (ss) RNA, which means it contains the genes or instructions to make viral proteins that will be used to make more of the virus.
Mumps Virus Infection and Symptoms
The mumps virus is highly contagious and is spread through droplets. If an infected person laughs, coughs, sneezes, or does anything that causes saliva or mucus to fly into the air, they can infect other people around them if those people inhale the saliva or mucus.
The problem with the mumps virus is that it has a long incubation period, 14-25 days. During this period, an infected person may not know they are sick. Some people never develop the symptoms of mumps at all. However, in about 15% of the population, more serious symptoms such as meningitis, encephalitis, and swelling of the ovaries (oophoritis) or swelling of the testes (orchitis) can occur.
The mumps virus was the most common cause of acquired deafness. Infection of the pancreas caused by the virus could lead to the development of juvenile diabetes, and infection of the testes and ovaries can lead to infertility.The initial symptoms of the mumps virus are similar to having a cold. This is because when infected droplets are inhaled, the lungs become infected.
All viral replication includes (1) entry, (2) replication and transcription, (3) translation, (4) assembly, and (5) budding. Let’s look at these steps in more detail:1.) Entry: The virus attaches and fuses with the cell membrane, which allows the negative-sense ssRNA genome to be released into the cytoplasm where replication occurs.
2.) Replication and transcription: The negative-sense ssRNA genome is converted, or transcribed, into mRNA as depicted in the cytoplasm as shown in 2a of the figure. The genome also serves as a means of replication as shown in 2b of this figure; this step also occurs in the cytoplasm.3.
) Translation: Proteins are made, or translated, from the viral mRNA on the ribosomes found in the cytoplasm.4.) & 5.) Assembly and Budding: The virus is assembled on the plasma membrane, and then it buds from the cell and the cycle starts again.
The mumps virus was a common childhood disease before vaccination became available for the virus and is a member of the paramyxoviridae virus family. The genome is a negative-sense single-stranded RNA, which means it contains the genes or instructions to make viral proteins that will be used to make more of the virus.
This negative-sense ssRNA is encased in a nucleocapsid, which is the capsid and genome together. Remember that a capsid is a structure made of repeating protein subunits called nucleoprotein that protects the viral genome and aids in replication inside the host cell.The nucleocapsid is surrounded by an envelope, a lipid bilayer, similar to the cell membrane that surrounds human cells, that is derived from the host cell membrane.
The envelope proteins includes proteins involved in fusion (F), attachment (HN), and assembly (M). The entire viral replication cycle occurs in the cytoplasm. The virus infects the parotid salivary glands causing them to swell, but it can also infect other salivary glands, meninges, brain, pancreas, testes, and ovaries. There is no cure, but it can be prevented with vaccination.