|Image is from Wikimedia Commons under a Creative Commons license|
This boy has the mumps, which is a viral disease. Most distinctively, it involves inflammation of the salivary glands, visible externally as a swollen upper neck and cheeks. Symptoms also include muscle aches, fever, tiredness, appetite loss, and headaches. Complications can occur, some of which are quite dangerous. Most frequent of all potential complications, postpubescent males can have swelling of the testes, which can lead to infertility. Postpubescent females can also have swelling of the breasts or ovaries, though this is less common. Mumps can lead to deafness as well, which may be permanent. Perhaps most concerning, however, is the possibility of encephalitis or meningitis: swelling or the brain and spinal cord, respectively.
Mumps is transmitted much like a cold or the flu: through droplets of mucus or saliva. Thus, the same rules apply when trying to avoid infection: wash hands thoroughly and often if there is a potential for exposure to the virus. Surfaces like doorknobs should be cleaned and touching of the face should be avoided. Infected individuals should be kept away from the very young and those with compromised immune systems.
Mumps is easily preventable through the common MMR (measles, mumps, rubella) or MMRV (the former plus varicella/chickenpox) combination vaccines, though the vaccine may be given individually as well. The vaccine is administered twice during early childhood, and widespread vaccinations in the United States has drastically reduced the incidence of the disease. However, the two-dose schedule is still only about 88% effective at preventing the disease. Despite this, annual incidence has been decreased by more than 99% since before the vaccination program began.
Sources are the Centers for Disease Control and Prevention, MedlinePlus, and the Mayo Clinic.