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Mumps is caused by the mumps virus, which belongs to a family of viruses known as paramyxoviruses. These viruses are a common source of infection, particularly in children.

When you get mumps, the virus moves from your respiratory tract (your nose, mouth and throat) into your parotid glands (saliva-producing glands found either side of your face), where it begins to reproduce. This causes the glands to swell.

The virus can also enter your cerebrospinal fluid (CSF), which is the fluid that surrounds and protects your brain and spine. Once the virus has entered the CSF, it can spread to other parts of your body, such as your brain, pancreas, testicles (in boys and men) and ovaries (in girls and women).

Mumps is an airborne virus and can be spread by:

• an infected person coughing or sneezing and releasing tiny droplets of contaminated saliva, which can then be breathed in by another person
• an infected person touching their nose or mouth, then transferring the virus onto an object, such as a door handle, or work surface; if someone else touches the object shortly afterwards, they can transfer the virus into their respiratory tract
• sharing utensils, such as cups, cutlery or plates with an infected person

People with mumps are usually most infectious from a few days before their parotid glands swell until a few days afterwards. For this reason, it's advisable to avoid work or school for 5 days after your symptoms first develop if you're diagnosed with mumps.

Mumps can also be passed on by people who are infected with the virus but don't have any obvious symptoms.