herpes zoster, infection of a ganglion (nerve center) with severe pain and a blisterlike eruption in the area of the nerve distribution, a condition called shingles. The causative organism is varicella zoster, a common, filtrable virus that is also known to cause chicken pox. Herpes zoster usually affects persons past middle life. It most often involves the area of the upper abdomen and lower chest, but may appear along other nerve pathways including that leading to the eye; serious ocular complications can lead to blindness. The disease can be treated with antivirals, and aspirin and other analgesics are used to relieve pain. Although it is generally nonrecurrent, it can permanently damage nerves and lead to postherpetic neuralgia, whose often severe, persistent pain is more difficult to control.