Yellow fever is caused by infection with a flavivirus. This virus replicates in the blood and tissues, potentially damaging the body's vital organs. The liver is often affected. When liver function declines, the skin and eyes become yellow, a condition known as jaundice, and the body's ability to form blood clots is compromised. Difficult-to-control bleeding may occur from areas such as the intestinesr. Damage to the heart, brain, and other vital organs can cause shock, coma, and increased susceptibility to bacterial infections. If a person survives a severe infection, it may take several months to fully recover.