What is it?

• Hepatitis A is a highly contagious liver infection caused by the hepatitis A virus. Hepatitis A is one of several types of hepatitis viruses that cause inflammation that affects your liver's ability to function.
• You're most likely to contract hepatitis A from contaminated food or water or from close contact with someone who's already infected. Mild cases of hepatitis A don't require treatment, and most people who are infected recover completely with no permanent liver damage.
• Practicing good hygiene — including washing your hands often — is one of the best ways to protect against hepatitis A. Effective vaccines are available for people who are most at risk.

Symptoms

Hepatitis A signs and symptoms typically don't appear until you've had the virus for a month. Signs and symptoms of hepatitis A include:

• Fatigue
• Nausea and vomiting
• Abdominal pain or discomfort, especially in the area of your liver on your right side beneath your lower ribs
• Loss of appetite
• Low-grade fever
• Dark urine
• Muscle pain
• Itching
• Yellowing of the skin and eyes (jaundice)

Signs and symptoms of hepatitis A usually last less than two months, but may last as long as six months. Not everyone with hepatitis A develops signs or symptoms.

Causes

Hepatitis A is caused by infection with the hepatitis A virus. The hepatitis virus is usually spread when a person ingests tiny amounts of contaminated fecal matter. The hepatitis A virus infects the liver cells and causes inflammation. The inflammation can impair liver function and cause other signs and symptoms of hepatitis A.

Hepatitis A virus can be transmitted several ways, such as:

• When someone with the virus handles the food you eat without first carefully washing his or her hands after using the toilet
• Drinking contaminated water
• Eating raw shellfish from water polluted with sewage
• Being in close contact with a person who's infected — even if that person has no signs or symptoms
• Having sex with someone who has the virus
• Receiving a blood transfusion with blood that contains the virus, though this is very rare

Risk factors

You're at increased risk of hepatitis A if you:

• Travel or work in regions with high rates of hepatitis A
• Are a man who has sexual contact with other men
• Use injected or noninjected illicit drugs
• Live with another person who has hepatitis A
• Work in a research setting where you may be exposed to the virusReceive clotting-factor concentrates for hemophilia or another medical condition

Complications

Continuing signs and symptoms of hepatitis A

A small number of people with hepatitis A will continue to experience signs and symptoms of infection for several weeks longer than usual. For these people, hepatitis A signs and symptoms may go away and then reappear over several weeks. Though the signs and symptoms occur over a longer period of time, this form of hepatitis A infection is not more serious than a hepatitis A infection that causes the usual signs and symptoms.

Acute liver failure

In rare cases, hepatitis A can cause acute liver failure, which is a loss of liver function that occurs suddenly. People with the highest risk of this complication include those with chronic liver diseases and older adults. Acute liver failure requires hospitalization for monitoring and treatment. In some cases, people with acute liver failure may require a liver transplant. 

Diagnosis

Blood tests are used to detect the presence of hepatitis A in your body. A sample of blood is taken, usually from a vein in your arm, and sent to a laboratory for testing. Your doctor may also discuss your signs and symptoms as part of making a diagnosis.

References:

http://www.who.int/features/qa/76/en/

https://en.wikipedia.org/wiki/Hepatitis

http://www.medicalnewstoday.com/articles/145869.php

http://www.healthline.com/health/hepatitis

https://www.nlm.nih.gov/medlineplus/hepatitis.html

http://www.cdc.gov/hepatitis/

http://www.cdc.gov/hepatitis/hcv/cfaq.htm