Final answer:
A viral infection that often involves the parotid glands, which swell noticeably, is mumps. The correct option is 4.
Step-by-step explanation:
Mumps is an infection of the parotid glands, which are the largest of the three pairs of salivary glands located between the ears and the jaw. It is caused by the mumps virus (MuV) and is characterized by symptoms such as fever, headache, muscle pain, weakness, fatigue, and loss of appetite.
Mumps is highly contagious and can be transmitted through respiratory droplets or contact with contaminated saliva. In serious cases, it can lead to complications such as encephalitis, meningitis, and inflammation of the testes, ovaries, and breasts. However, thanks to effective vaccination, mumps infections rarely cause sterility. Hence, 4 is the correct option.