YELLOW FEVER
Yellow fever Endemic zones in Africa.
Yellow fever is an acute viral disease transmitted by the mosquito genus Aedes. It is an important cause of hemorrhagic illness in many African and South American countries despite existence of an effective vaccine. The yellow refers to the jaundice symptoms that affect some patients.
The virus remains silent in the body during an incubation period of three to six days. Then there are two disease phases; while some infections have no symptoms the first, acute phase is normally characterized by fever, muscle pain (with prominent backache), headache, shivers, loss of appetite, and nausea or vomiting. The high fever is often associated with a slow pulse (known as Faget's sign). After three or four days most patients improve and their symptoms disappear. Fifteen percent of patients, however, enter a toxic phase within 24 hours. Fever reappears and several body systems are affected. The patient rapidly develops jaundice and will normally complain of abdominal pain and profuse vomiting. Bleeding can occur from the mouth, nose, eyes, and stomach. Once this happens, blood appears in the vomit and feces. Kidney function will also deteriorate; this can range from abnormal protein levels in the urine (proteinuria) to complete kidney failure with no urine production (anuria). Half of the patients in the "toxic phase" die within fourteen days. The remainder normally recover without significant organ damage.
In 1937 a vaccine was developed for yellow fever that gives a ten-year or more immunity from the disease and effectively protects people traveling to affected areas At the same time it was being used a means to control the disease. A booster every ten years is required to maintain immunity. There is no true cure for yellow fever, therefore vaccination is important. Treatment is strictly supportive. Fluid replacement, fighting hypotension and blood transfusions are only needed in severe cases. In cases that result in acute renal failure, dialysis may be necessary. A fever victim needs to get lots of rest, fresh air, and drink plenty of fluids.
Historical reports have claimed a mortality rate of between 1 in 17 (5.8%) and 1 in 3 (33%). The WHO fact-sheet on yellow fever, enter a "toxic phase" and that half of that number die within ten to fourteen days, with the other half recovering.
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Yellow fever in its host.
Administration of the yellow fever vaccine.