Overview
Yellow fever is a type of zoonotic viral haemorrhagic fever caused by the yellow fever virus, which is transmitted by Aedes mosquitos. If severe enough, it can cause fever, haemolytic jaundice, and acute kidney injury. Other examples of viral haemorrhagic fever include dengue fever and Ebola.
Pathophysiology
Upon entering the body, it replicates in nearby lymph nodes and spreads via the blood to other lymphoid tissues. It has an incubation period of around 3-6 days followed by viraemia and infection of the liver and kidneys. Disseminated intravascular coagulopathy (DIC) can occur, leading to widespread haemorrhage, and a cytokine storm can lead to shock and multiple organ failure, which can lead to death.
Presentation
Overview
Features include:
- Initial 3-4 days of acute fever, headache, malaise, and myalgia followed by a brief remission
- After a few days, a second episode of high fever occurs, along with nausea, vomiting, abdominal pain, and drowsiness
- Hepatitis, jaundice, and haemorrhage follow (e.g. haematemesis, melaena, petechiae, purpura, epistaxis)
- Oliguria and uraemia can develop as acute kidney injury occurs
- Bradycardia may be seen
Investigations
Overview
- Full blood count (FBC) – may show thrombocytopenia
- Coagulation assay – may show elevated PT, APTT, fibrinogen degradation products and low fibrinogen
- Liver function tests (LFTs) – may show elevated aminotransferases and bilirubin
- Reverse transcription polymerase chain reaction (RT-PCR) – may confirm the presence of yellow virus RNA
