Yellow Fever, also known as Yellow Jack or the Yellow Plague, was one of the most devastating and feared diseases throughout the Americas in the 18th and 19th centuries. The disease was originally present in monkeys that originated from West Africa. Humans were not infected with this disease until they encroached in on areas where the infected monkeys were present. When they entered the area, the humans had no immunity to the disease. The disease was able to leave West Africa and spread to the New World due to seafaring trade. The mosquitoes carrying Yellow Fever live about 70 to a maximum of 225 days, which makes survival on a boat possible. When the virus reached the Americas it became an epidemic due to Caucasians and Native Americans having no resistance to the virus. On the other hand, many of the slaves located in the Americas who were from West Africa, when infected with the virus only showed mild to moderate symptoms. This shows that generations in West Africa were able to build up a resistance to Yellow Fever over time. It was not until 1901 that scientists were able to figure out that the disease was spread through the female Aedes Aegypti mosquito. It is spread when the mosquito sucks the blood from an infected individual. The virus then goes into the mosquito's system where it infects the salivary glands. When the mosquito bites another animal, the virus is released from the salivary glands and is transmitted into the now infected individual. When a person is infected with Yellow Fever, the first stage is an infection with a fever of 102 to 105 degrees Fahrenheit that lasts three to four days. During this time, headache, back and muscle pain, nausea, and vomiting are severe. The second stage of the infection is remission, in which the person has no fever. This can sometimes last just a couple of hours. During this time, the person’s temperature falls to 99 to 100 degrees Fahrenheit, the headache disappears, and the person feels better. Then the third stage begins. The person’s temperature quickly rises again and the symptoms in the first stage reappear, but in a more severe form. During this time the person becomes increasingly agitated and anxious. Liver, heart and/or renal failure often follow. Jaundice develops at about the fourth or fifth day of this stage. Within six to seven days, death often follows. Those who do survive the virus remain ill, usually for another seventeen to thirty days. Afterwards, recovery is slow and marked with fatigue.