A: A virus typically transmitted by ingesting contaminated food or water, this disease flourishes in world regions where sanitation and hygiene are poor; it can also thrive in day-care centers. The prime source of infection is fecal matter. Transmission can occur after using dirty needles, eating with dirty utensils, and consuming contaminated shellfish. Most people recover without any serious health problems.
A vaccine was approved by the Food and Drug Administration this February and is recommended for travelers to high-risk countries, residents of high-risk communities, IV drug users, gay men, and people with chronic liver disease.
B: First identified in the early '60s, this virus is endemic in many parts of the world, including Africa and Asia, where hepatitis B-related liver cancer is a leading cause of death.
The disease doesn't always produce symptoms, and many people only discover they have it after donating blood and being told they tested positive. The virus is transmitted by a blood or body-fluid exchange only; it is not transmitted by sharing a classroom with a carrier, or nonsexual contact such as holding hands.
Those developing hepatitis B are believed to be infectious for several weeks before the onset of flulike symptoms. If you have unprotected sex or share needles with a known carrier, doctors advise getting an immediate injection of hepatitis B immune globulin (HBIG), which can help prevent infection. Note: Getting one hepatitis does not protect you from getting another.
C: Once called non-A, non-B, this hepatitis was not completely defined until 1989; a way to identify it in patients wasn't commercially available until 1990. Like B, it is transmitted in blood and blood products, primarily through transfusions, IV drug use, health-care work, and, to a lesser extent, sexual contact. It appears to advance gradually over 10 to 40 years, in some people causing fatigue, nausea, jaundice, and an increased risk of liver cancer.
In 1988, researchers at Emeryville's Chiron Corp. developed an antibody test to screen blood-bank donations for evidence of C, which at the time was the most frequent contaminant in the nation's blood supply (the problem today has all but been eradicated). Interferon and experimental treatments prove helpful for some, but there are no known cures. Mickey Mantle acquired hepatitis C through knee surgery, Chiron officials say, which along with his legendary liquor consumption necessitated his liver transplant this year.
D: A relatively uncommon form -- about 95 percent of all hepatitis in the U.S. is A, B, or C -- this virus is also known as delta hepatitis. It primarily affects drug users already infected with hepatitis B.
E: This virus resembles A, but is primarily found in the Indian Ocean region.