Yellow fever (also called black vomit or sometimes The American Plague) is an acute viral disease. It is still an important cause of hemorrhagic illness in several African and South American countries despite existence of an effective vaccine. In the past it was a source of several devastating epidemics.
Mosquitos are the primary disease vector in transmission of the disease from forest monkeys to man and in man-to-man transmission. The mosquitos involved are Aedes simpsoni, Aedes africanus, and Aedes aegypti in Africa; and the Haemagogus and Sabethes genera.
The course of the disease varies from an inapparent infection to an intense feverish illness with high mortality rate. There is a difference between disease outbreaks in rural or forest areas and in towns. Disease outbreaks in towns and non-native people are usually more serious.
After a 3 to 6 day incubation period the typical symptoms that arise are fever, muscle aches, headache and backache. Other symptoms may include a red tongue, flushed face, and reddening of the eyes may also be symptoms of the disease. In a proportion of cases there is also involvement of internal organs - liver, kidneys and the heart. There may be hemorrhage from the digestive tract (bloody vomit). Later the disease is sometimes complicated by jaundice with liver failure and/or renal insufficiency with proteinuria. If the disease progresses, delirium, seizures and coma ensue. Hypotension and dehydration are also common. Mortality is around 5%. Patients who die usually do so within six to seven days from the onset.
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Yellow fever is one of the few diseases in the world for which some countries have a legal requirement for vaccination for someone travelling to an affected area. There countries also usually have regulations requiring quarantine for people who arrive from yellow fever endemic areas who do not provide evidence of their having being vaccinated against yellow fever. This is because the vector for transmission of yellow fever, the Aedes mosquito, exists in other tropical parts of the world which are not affected by yellow fever and an outbreak could potentially erupt if the disease is inadvertently brought in.
See also : Lassa fever.
A vaccine for yellow fever was developed which gives a 10-year immunity from the disease and effectively protects people travelling to the affected areas and being a means to control the disease at the same time. Insecticides, protective clothing and screening of houses are helpful but not always enough. In affected areas some sort of mosquito control has proved effective in decreasing number of cases.
There is no specific cure for the disease; therefore vaccination is so
important. Treatment is symptomatic and supportive only. Fluid replacement, fighting hypotension and transfusion of blood derivates is mostly needed in severe cases. In renal insufficiency - dialysis.
See also : Lassa fever.