Mumps is a disease caused by the mumps virus, which is a member of the paramyxoviridae family.
This is actually a large family of viruses which includes measles virus and parainfluenza
viruses, and all of these tend to affect children the most.
Mumps only affects humans and and is spread by tiny respiratory droplets that are small
enough to be carried short distances in the air, so mumps virus is extremely contagious
and anyone near a person with mumps is at risk for getting the disease as well.
The mumps virus has a single strand of RNA and a viral polymerase enzyme surrounded by
a phospholipid bilayer envelope studded with viral proteins hemagglutinin-neuraminidase,
or HN protein, and fusion or F protein.
The HN protein allows the virus to stick to a potential host cell, and cut itself loose
if necessary, and the F-protein which fuses the viral and cell membranes together allowing
the mumps virus to enter the cell.
Once mumps enters a cell, the single stranded RNA, which is negative sense, gets transcribed
by the viral polymerase enzyme, into a complementary positive sense strand of mRNA, which can then
be translated by the host cell ribosomes into new copies of the envelope proteins and the
viral polymerase, which get assembled into new viruses.
What also ends up happening with these, though, is that those HN and F-proteins on the cell
surface now bind other cells, so they actually end up bind epithelial cells to one another,
which forms a clump of connected cells called a multinucleated giant cell or a syncytium.
Mumps enters the body and first infects the epithelial cells of the nasopharynx, where
it starts replicating and causing local damage to the tissue.
From there, it can cause viremia or virus in the blood, and reach various organs and
tissues.
The mumps virus has tropism, or preference for, the parotid salivary glands, and the
most classic finding in mumps is swelling of parotid salivary glands either on one side
or on both sides, sometimes with an associated earache.
The swollen parotid gland lifts the earlobe up and out and obscures the angle of the jaw,
and can sometimes cause trismus which is spasm of the muscles of mastication or chewing.
Mumps also has affinity for the central nervous system, and can cause meningitis, which is
an infection of the lining of the brain, as well as encephalitis, which is an infection
of the brain tissue itself.
These infections can cause symptoms ranging from those that feel like the common cold,
like headache and neck stiffness, as well as more severe symptoms like difficulty with
balance and hearing loss, but in general, the infection is self-limited and symptoms
go away as the body recovers.
In boys, usually in adolescents and young men, mumps can infect the testicles and epididymis,
and cause orchitis and epididymitis, respectively, most often on just one side.
This can cause testicular atrophy in some men, as well as a decrease in sperm count
and sperm motility, but rarely does this cause infertility.
Less commonly, mumps can infect the kidneys, and cause glomerulonephritis, which eventually
leads to hematuria and proteinuria—blood and urine in the urine.
It can also affect the joints, causing arthritis, usually in the large joints like the hips,
knees, ankles, and shoulders.
And it can affect the heart causing myocarditis, as well as the pancreas, causing pancreatitis.
As a final note, pregnant women with mumps are not at an increased risk of having a baby
with congenital defects.
Alright, like a lot of other viruses, diagnosis is done by looking at antibody titers, though
for treatment there aren’t any effective antivirals for mumps.
For prevention, Individuals with mumps, particularly young children, are usually kept isolated
for 5 days after the onset of symptoms to prevent it from spreading.
Best of all for prevention, though, is the mumps vaccine which is about 90% effective
at preventing the disease in the first place.
The vaccine is a live attenuated vaccine, which means that it’s a weakened mumps virus
which is not infectious, but still stimulates the immune system to generate a strong response
to prevent a future infection from the actual wild-type mumps virus.
Mumps vaccine has reduced the occurrence of mumps dramatically, with outbreaks happening
most often in areas where children aren’t vaccinated.
Alright, as a quick review, mumps is very contagious and spreads through the air by
respiratory droplets, and most classically infects the salivary parotid glands, causing
them to become swollen, but can also cause meningitis, encephalitis, orchitis, and epididymitis.
Luckily, there is mumps vaccine that is safe and effective in preventing nearly 90% of
cases.
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