There are seven known hepatitis viruses, which are labeled A, B, C, D, E, F, and G. Hepatitis A, E, and F viruses are transmitted through the ingestion of contaminated food or water (called the fecal-oral route); the spread of these agents is aggravated by crowded conditions and poor sanitation. The B, C, D, and E viruses are transmitted mainly by blood or bodily fluids; sexual contact or exposure to contaminated blood are common modes of transmission The signs and symptoms of acute viral hepatitis result from damage to the liver and are similar regardless of the hepatitis virus responsible. Patients may experience a flulike illness, and general symptoms include nausea, vomiting, abdominal pain, fever, fatigue, loss of appetite, and, less commonly, rash and joint pain. The onset of hepatitis A usually occurs 15 to 45 days after exposure to the virus, and some infected individuals, especially children, exhibit no clinical manifestations. In the majority of cases, no special treatment other than bed rest is required; most recover fully from the disease. Hepatitis A does not give rise to chronic hepatitis. The severity of the disease can be reduced if the affected individual is injected within two weeks of exposure with immune serum globulin obtained from persons exposed to hepatitis A virus. This approach, called passive immunization, is effective because the serum contains antibodies against hepatitis A virus. Hepatitis B may occur as an acute disease, or, in about 5 to 10 percent of cases, the illness may become chronic and lead to permanent liver damage. Symptoms usually appear from 40 days to 6 months after exposure to the hepatitis B. Those persons at greatest risk for contracting hepatitis B include intravenous drug users, sexual partners of individuals with the disease, health care workers who are not adequately immunized, and recipients of organ transplants or blood transfusions. A safe and effective vaccine against HBV is available and provides protection for at least five years. Passive immunization with Symptoms of hepatitis C usually appears within six to nine weeks after exposure. Hepatitis C virus appears to be transmitted in a manner similar to hepatitis B virus. Hepatitis C has a greater propensity than hepatitis B to develop into chronic liver disease. Alcoholics who are infected with hepatitis C are more prone to develop cirrhosis. Infection with hepatitis D virus may occur at the same time infection with hepatitis B virus occurs, or hepatitis D virus may infect a person already infected with hepatitis B virus. The latter situation appears to give rise to a more serious condition, leading to cirrhosis or chronic liver disease. Alpha interferon is the only treatment for hepatitis D virus infection. Preventing infection with hepatitis B virus also prevents hepatitis D virus infection. Hepatitis E virus is transmitted in the same manner as hepatitis B virus, and it, too, only causes acute infection. However, the effects of infection with hepatitis E virus are more severe than those caused by hepatitis A virus, and death is more common. The risk of acute liver failure from infection with hepatitis E virus is especially great for pregnant women. In less-developed countries, including Mexico, India, and those in Africa, hepatitis E virus is responsible for widespread epidemics of hepatitis that occur as a result of ingestion of contaminated water or food enteric transmission.