There are five primary types of viral hepatitis: A, B, C, D and E.

Hepatitis A (HAV) is caused by eating food or drinking water that is contaminated with the feces of a person infected with the hepatitis A virus. For example, people can contract hepatitis A by eating raw or undercooked seafood harvested from contaminated waters, by eating produce that was fertilized with human waste, by eating at restaurants where infected employees did not wash their hands after using the restroom or even by touching their mouth after shaking hands with an infected person.

Anal-oral contact can also cause hepatitis A. In rare cases, hepatitis A may be passed through contact with infected blood. Hepatitis A is rarely passed from a mother to her baby. It can, however, occasionally play a role in premature labor. Hepatitis A makes up about one-third of all hepatitis infections in the United States, according to the National Women’s Health Resource Center.

Although hepatitis A causes the liver to swell, the condition generally improves on its own and is not chronic. Cases tend to be mild in young children and more severe in older children and adults. In the majority of cases, a person’s liver typically makes a full recovery within two months of the infection. In rare cases, a life-threatening condition called fulminant hepatitis may develop after hepatitis A.

After a person recovers from hepatitis A, the virus no longer remains in the body and the person cannot become infected with hepatitis A again. However, patients who recover from infection with hepatitis A remain vulnerable to infections from other forms of hepatitis.

People at greatest risk for hepatitis A include:

• International travelers.
  
  
• People living in areas of frequent hepatitis A outbreaks, especially vulnerable populations such as children and employees at daycare facilities, men who have sex with men and people who inject illegal drugs.
  
  
• People who live with or have sex with an infected person.
  
  
• Patients with hemophilia (a disease that prevents normal blood clotting) or who receive clotting-factor concentrates as treatment for a medical condition. In rare cases, hepatitis A can be transmitted through blood transfusions.

Hepatitis B (HBV) is caused by contact with bodily fluids of a person infected with the hepatitis B virus. It can be contracted through sexual intercourse with an infected person or through sharing intravenous (I.V.) needles with an infected person during illegal drug use. It can also be transmitted from an infected mother to her baby during childbirth. About 1.25 million people are chronically infected with the virus in the United States, according to the CDC. It is about 100 times more infectious than the human immunodeficiency virus (HIV), which causes acquired immune deficiency syndrome (AIDS). Approximately 20 to 30 percent of patients with hepatitis B contracted the virus during childhood.

Most people who contract hepatitis B through sexual or I.V. transmission experience acute infections. Hepatitis B causes the liver to swell, and in some cases liver damage will occur. It also raises the risk for infection with hepatitis C and the human immunodeficiency virus (HIV; the virus that causes acquired immune deficiency syndrome [AIDS]). In most cases, the body rids itself of the virus after several months, and becomes immune to further infections. However, in other cases, such as when the infection is acquired as a newborn or an infant, the virus may become chronic, scarring the liver (cirrhosis), or causing liver failure or liver cancer.

According to the CDC, the risk of chronic infection with hepatitis B decreases with age, affecting very few individuals over the age of 5.

Many people with chronic hepatitis B may experience no symptoms or mild, flu-like symptoms. Approximately 15 to 25 percent of patients with chronic hepatitis B infection will die from the disease.

Of all the hepatitis viruses, hepatitis B poses the greatest risk in pregnancy. In some cases, mothers with hepatitis B transmit the infection to their child when their infected blood enters the baby’s body during the birthing process. In other cases, the child may obtain the virus during the pregnancy. There are no treatments to prevent this from happening. According to the March of Dimes Birth Defects Foundation, up to 20,000 women with hepatitis B give birth each year.

Mothers who have hepatitis B can breastfeed their child as long as the baby receives a shot called H–BIG (hepatitis B immune globulin) and a shot of hepatitis B vaccine within the first 12 hours after birth.  Hepatitis B shots significantly reduce the likelihood that the baby will acquire the infection. Without treatment, approximately half of babies born to mothers with hepatitis B may acquire the infection, according to the March of Dimes Birth Defects Foundation. The majority of these babies become lifelong carriers of the virus, with a high risk of developing serious liver disease and liver cancer as adults.

People at greatest risk for hepatitis B include:

• International travelers
  
  
• People who live with or have sex with an infected person
  
  
• Men who have sex with men
  
  
• People who use illegal drugs that are injected
  
  
• Children of immigrants who come from areas where the disease is endemic
  
  
• Children born to infected mothers
  
  
• Healthcare workers
  
  
• Hemodialysis patients
  
  
• People who received a blood transfusion or blood product before July 1992, or who received clotting factors made before 1987

Hepatitis C (HCV) is most often transmitted through sharing needles with an infected person during illegal drug use or through other contact with infected blood. Less commonly, it is spread through sexual contact, or to dialysis patients by contaminated equipment. The virus can also be transmitted from mother to child during childbirth.

During the 1970s and 1980s, researchers were aware of transmission of what was called “non-A, non-B hepatitis.” Many people contracted it from blood transfusions during surgery. This virus was identified as hepatitis C in the late 1980s and screening for it in the blood supply began in the early 1990s. In many cases, people infected with the virus have no symptoms and are not even aware of their infection. However, most people with hepatitis C having swelling of the liver that manifests as a chronic condition. This leads to chronic liver diseases such as cirrhosis, liver failure and liver cancer in up to 70 percent of patients.

An estimated 3.9 million Americans are infected with hepatitis C, and 2.7 million Americans are chronically infected with the virus, according to the CDC. Hepatitis C is the leading reason for liver transplants in the United States, according to the U.S. Department of Health and Human Services. In some cases, hepatitis C resolves on its own. However, the virus kills between 1 and 5 percent of those infected with it. People with hepatitis C infections are at higher risk for being infected with hepatitis B or HIV.

There are six known genotypes and 50 additional subtypes of hepatitis C. Identifying the specific genotype of hepatitis C will help in making treatment recommendations. For example patients with genotype 1 typically do not respond to treatment as well as patients with genotype 2 or 3 do.

People at greatest risk for hepatitis C include:

• People who have sex with an infected person, or who have multiple sex partners
  
  
• People who use drugs that are injected
  
  
• Healthcare workers
  
  
• Children born to infected mothers
  
  
• Hemodialysis patients
  
  
• People who received a blood transfusion or blood product before July 1992, or who received clotting factors made before 1987

Hepatitis D (HDV) is caused by contact with a person infected with this virus. It can occur through sexual contact or by sharing I.V. needles with an infected individual. Hepatitis D can also be transmitted from an infected mother to her baby during childbirth. However, a person must be infected with hepatitis B to become infected with hepatitis D.

Hepatitis D causes swelling of the liver and it can lead to liver disease and cirrhosis. Acute liver failure is more likely in patients with hepatitis D than in those who have hepatitis B alone. In some cases, hepatitis D resolves on its own.

People at greatest risk for hepatitis D include:

• People already infected with hepatitis B
  
  
• People infected with hepatitis B who use drugs that are injected
  
  
• People infected with hepatitis B who live with or have sex with someone infected with hepatitis D
  
  
• People infected with hepatitis B who received a blood transfusion or blood product before July 1992, or who received clotting factors made before 1987

Hepatitis E (HEV) infection occurs after consuming food or water contaminated with feces from an infected person. The risk of infection is greater in areas of the world outside the United States that have high rates of hepatitis E infection, and it typically affects young to middle-aged adults. Hepatitis E cannot develop into a chronic infection.

Hepatitis E causes swelling of the liver, but does not usually cause damage and resolves on its own. However, pregnant women and their babies are at increased risk of dying from infection. Pregnant women are especially at risk during their third trimester. The mortality rate among pregnant women is 20 percent, according to the National Women’s Health Resource Center.

People at greatest risk for hepatitis E include:

• International travelers
  
• People living in areas where hepatitis E outbreaks are common
  
• People who live with or have sex with someone infected with hepatitis E

In some cases, viral hepatitis cannot be attributed to any of these primary types. Such cases are classified as non-A-E hepatitis. The cause of this form of hepatitis remains unknown.

Other causes of hepatitis include alcohol, drugs, toxins such as industrial chemicals, bacteria, syphilis, toxoplasmosis, and other viruses, including cytomegalovirus and Epstein-Barr (mononucleosis).