Field of Science

Virus of the week: MUMPS VIRUS (MuV)

In order to better understand (and maybe even enjoy - is that the right word?) viruses, I think it is time to meet and greet a couple of them; this is why I am starting a weekly tradition here at Ro6 - "Virus of the week". I will introduce a virus; discuss its importance; highlight the important aspects of its biology and how it infects its hosts.

The first virus shown here is one currently close to my heart: the mumps virus (MuV). As part of my PhD work, I am using this virus to understand its molecular biology and how it causes disease in its host - humans. Not much is known about the basic biology of this unique human pathogen but that is beginning to change.

What is mumps?

Mumps, what used to be a common childhood illness, is characterised by the swelling of the salivary glands (parotitis) following infection yet something not commonly known is that it can also very easily infect the central nervous system with rates nearing 50% of those with mumps (see the NHS info site here). Prior to the introduction of vaccination programs it was one of the biggest causes of non-bacterial meningitis worldwide, although not life-threatening, meningitis and encephalitis constitute serious disease. Also, very importantly, in males it is very common for the testis to swell massively causing great pain and discomfort, possibly leading to reduced fertility. There are also a number of much rarer complications associated with MuV infecton, including infection of the heart muscle; the pancreas and the inner ear which can lead to deafness (Lancet review here). Part of my research is trying to understand why - at the molecular level - MuV causes these symptoms and infects these organs rather than others.

Why is it important?

The mumps virus
 But why is it important to study MuV, especially as we have a good vaccine? Well, despite this highly effective vaccine - that HAS worked very well in the past - mumps is still currently circulating worldwide. A good example is the ongoing Scottish outbreak but well publicised outbreaks across the US and UK also highlight this. The reasons why, despite being vaccinated, MuV can infect a person are currently unknown. If we have a good vaccine and the ability to vaccinate people easily yet can't eradicate the mumps virus, what hope do we have for a virus which is more difficult to immunise? Also, in countries lacking mumps immuisation, mumps can contribute to profound morbidity and mortality; mumps is therefore still a global problem! For WHO figures see here.

Mumps virus molecular biology

Viruses are, at the most basic level, very small packages of nucleic acids and proteins packaged in a protective coating which can either be made of proteins (capsid) or fats (an envelope). The mumps virus comes from a group of viruses that whose genome is made out of RNA - not DNA like you and I have - and strangely, it is also only single-stranded while ours is double-stranded; we say that this RNA is 'negative sense' in that it is complementary to its mRNA molecules. The mumps genes are lined up across this single RNA molecule encoding for proteins involved in cell entry, replication and immune evasion.

Other viruses with single-stranded, negative-sense RNA genomes include many important human and animal pathogens: measles virus, respiratory syncitial virus, ebolavirus and the henipaviruses. More specificaly MuV is a Rubulavirus found within the family Paramyxoviridae. Like other viruses, MuV carries out its entire active lifecycle within the cell and uses its extracellular form (shown above) to infect new cells allowing the virus genome access to the cell cytoplasm where replication and gene expression take place and full-blown infection can begin.

Evolutionary tree of Paramyxovirus relationships - notice mumps virus (MuV), a rubulavirus.

So how does the mumps virus cause mumps?

Just like Influenza, mumps is transmitted through aerosol particles that we breathe in and out which allows the virus access to our respiratory tract - a very nice point of entry of many viruses. MuV is believed to first replicate along our airways in the epithelial cell lining and then is somehow able to spread throughout the body, possibly via infection of your bodies immune cells or maybe just release of virus particles into the bloodstream. Infection of the salivary glands, brain, testis and pancreas follows giving rise to the common symptoms known as mumps. Virus particles are finally released back into your airways allowing the spread between person to person and once your immune response kicks in, the virus infection is cleared up hopefully without any long-term problems.

What does the future hold for mumps research?

A lot of this basic knowledge outlined above on mumps infection has been seen only through studying of other viruses and there is so much more basic mechanisms to find out. The advent of modern molecular biology techniques and protocols has allowed for a renewed interest in studying this basic biology of viruses, including mumps. The ability to alter a virus genome and investigate whether it has biologically changed has facilitated a much better understanding of viral infection, replication and evolution. This has - and is being - applied to the study of mumps, however, there is still much work to be done to catch up with other viruses. Maybe, before we have had a chance to understand mumps biology we will have eradicated indigenous mumps transmission worldwide and it will no longer be important.
Galazka AM, Robertson SE, & Kraigher A (1999). Mumps and mumps vaccine: a global review. Bulletin of the World Health Organization, 77 (1), 3-14 PMID: 10063655

Walker J, Huc S, Sinka K, Tissington A, & Oates K (2011). Ongoing outbreak of mumps infection in Oban, Scotland, November 2010 to January 2011. Euro surveillance : bulletin europeen sur les maladies transmissibles = European communicable disease bulletin, 16 (8) PMID: 21371413

1 comment:

  1. I can't find any info on how long it lasts. I have pain still in my cheek in a small area that swelled up over 2 mo. It started after a dental appointment and I attributed that and jaw pain to that appointment. Other symptoms that developed shortly after that were headache and sore throat with some swelling there and under the chin. Later came ear pain. The headache was the worst part, lasting more than 2 months. I am trying to figure out if it is actually mumps. I never seemed to have a fever. At one point I had a little difficulty saying something complicated. Does that sound like mumps to you?


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