The liver, the body's largest gland, performs many important tasks, but is also vulnerable to many illnesses. At least five types of hepatitis, labeled with the letters A–E, are caused by viruses. The most common are hepatitis A, acquired through contaminated food and water; hepatitis B, which usually travels via sexual activity or shared needles; and hepatitis C, generally passed through shared needles. Some other types, including alcoholic hepatitis (caused by drinking too much alcohol), aren't infectious. There are vaccines for types A and B, and drug treatments for A, B, and C, though the drugs aren't always effective.