Yellow fever natural history
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Initial symptoms of yellow fever start 3-6 days after the mosquito bite, these include sudden onset of fever, chills, severe headache, back pain, general body aches, nausea and vomiting, fatigue, and weakness. Most people improve after these initial symptoms. However, roughly 15% of people will have a brief period of hours to a day without symptoms and will then develop a more , severe form of yellow fever disease. Possible complications include coma, disseminated intravascular coagulation (DIC), kidney failure, liver failure and shock. The prognosis is good in the majority of patients, infected persons will be asymptomatic or have mild disease with complete recovery.
Natural History, Complications and Prognosis
- In its mildest form, yellow fever is a self-limited infection characterized by sudden onset of fever and headache without other symptoms.
- Other patients experience an abrupt onset of a high fever (up to 104°F/40° C), chills, severe headache, generalized myalgias, lumbosacral pain, anorexia, nausea, vomiting, and dizziness.
- The patient appears acutely ill, and examination might demonstrate bradycardia in relation to the elevated body temperature (Faget's sign).
- The patient is usually viremic during this period, which lasts for approximately 3 days.
- Many patients have an uneventful recovery, but in approximately 15% of infected persons, the illness recurs in more severe form within 48 hours following the viremic period.
- After the third to sixth day of the onset of the symptoms the patient may present return of the fever, vomiting, renal failure (oliguria), jaundice, epigastric pain and hemorrhagic diathesis. The viremia terminates during this stage and the antibodies appear in the blood. The patient may evolve with multiorgan failure during this phase. Also in this stage, AST concentrations might exceed ALT, probably due to myocardial and skeletal muscle damage. Serum creatinine and bilirubin levels also rise at this stage. Hemorrhagic manifestations may include petechiae, ecchymoses, epistaxis, melena, metrorrhagia, hematuria, haematemesis, and oozing blood from the gingiva and needle-puncture sites. Laboratory studies may show thrombocytopenia, reduced fibrinogen levels, presence of fibrin split products, reduced factors II, V, VII, VIII, IX and X, which suggest a multifactorial cause for the bleeding with a consumption coagulopathy. Myocardial disfunction may be demonstrated by abnormalities in the ST-T segment in the electrocardiogram. Encephalitis is very rare.
The possible complications are:
- Death (approximately 20-50% of the patients with the hepatorenal disease die after 7-10 days of the onset )
- Disseminated intravascular coagulation (DIC)
- Kidney failure
- Liver failure
- Secondary bacterial infections
- The majority of infected persons will be asymptomatic or have mild disease with complete recovery. 
- In persons who become symptomatic but recover, weakness and fatigue may last several months.
- Among those who develop severe disease, 20% - 50% may die.
- Those who recover from yellow fever generally have lasting immunity against subsequent infection.