Yellow fever

Yellow fever
Erskine Palmer, Ph.D. · Public domain · source
Name	Yellow fever
Field	Infectious disease
Symptoms	Fever, jaundice, hemorrhage
Complications	Liver failure, renal failure, hemorrhagic fever
Onset	3–6 days
Causes	Yellow fever virus (Flavivirus)
Risks	Aedes aegypti, Haemagogus, travel to endemic regions
Diagnosis	Serology, PCR
Prevention	Vaccination, vector control
Treatment	Supportive care
Deaths	Variable; severe case fatality up to 50%

Yellow fever is an acute viral hemorrhagic disease caused by a flavivirus transmitted by mosquitoes. It presents with systemic febrile illness, hepatic dysfunction leading to jaundice, and in severe cases hemorrhage and multiorgan failure. Endemic in parts of sub-Saharan Africa and tropical South America, the disease has shaped exploration, colonial campaigns, and public health initiatives across centuries.

Signs and symptoms

Initial presentation typically includes sudden onset of high fever, chills, headache, myalgia and backache associated with nausea and vomiting; patients may develop relative bradycardia and conjunctival injection. During the toxic phase a subset progress to jaundice, epistaxis, hematemesis and melena reflecting hepatic and gastrointestinal involvement, often accompanied by oliguria and delirium. Laboratory abnormalities include elevated bilirubin, transaminases, coagulopathy with prolonged prothrombin time and thrombocytopenia; severe cases may manifest into shock and multiorgan failure.

Cause and transmission

The etiologic agent is a single-stranded positive-sense RNA virus of the genus Flavivirus in the family Flaviviridae. Transmission occurs via the bite of infected female mosquitoes, principally urban-cycle Aedes aegypti and sylvatic cycles involving neotropical Haemagogus and African Aedes africanus species. Human outbreaks are amplified in densely populated urban zones and facilitated by travel between endemic areas such as Nigeria, Democratic Republic of the Congo, Brazil, Peru and Angola. International control efforts intersect with agencies like the World Health Organization, Pan American Health Organization and national ministries such as Ministry of Health (Brazil). Historical vectors and shipping routes linked outbreaks to port cities including Philadelphia, Rio de Janeiro, Cartagena (Colombia), and Cuba.

Pathophysiology

After inoculation the virus replicates in regional lymph nodes and disseminates hematogenously to target organs, notably the liver, kidneys and bone marrow. Hepatocellular necrosis, particularly of midzonal hepatocytes, yields impaired bilirubin conjugation and coagulopathy; viral tropism implicates interactions with hepatocyte receptors and innate immune pathways. Dysregulated immune responses and endothelial dysfunction contribute to hemorrhage and capillary leakage similar to mechanisms studied in other flavivirus infections like Dengue fever and West Nile virus. Histopathology demonstrates Councilman bodies and necrosis; severe disease correlates with high viraemia and impaired interferon-mediated control.

Diagnosis

Definitive diagnosis relies on laboratory testing: detection of viral RNA by reverse transcription PCR during the early viremic phase, and serology demonstrating specific IgM or a fourfold rise in neutralizing antibodies on plaque reduction neutralization testing. Antigen detection and viral isolation in cell culture are additional modalities performed in reference laboratories. Differential diagnosis commonly includes Malaria, Leptospirosis, Lassa fever, Dengue fever, Hepatitis A, and Yellow fever vaccine-associated viscerotropic disease after recent immunization events. Clinical and epidemiologic context—travel history to endemic countries, exposure to mosquito habitats, and vaccination status—guides testing pathways coordinated with public health authorities such as Centers for Disease Control and Prevention.

Prevention and vaccination

Prevention emphasizes a live-attenuated vaccine produced from the 17D strain, recommended for travelers and residents of endemic regions and required by entry regulations for certain countries. Single-dose vaccination typically confers long-term immunity, with booster recommendations evolving under guidelines from the World Health Organization and national advisory committees like the Advisory Committee on Immunization Practices. Vector control strategies include mosquito surveillance, insecticide-treated materials, elimination of breeding sites and community campaigns exemplified by historical programs in Panama and contemporary initiatives in Kenya and Brazil. International coordination through International Health Regulations influences vaccination certification and outbreak response.

Treatment and prognosis

No specific antiviral therapy is approved; management is supportive and may require intensive care for hemodynamic stabilization, blood product transfusion, renal replacement therapy, and management of coagulopathy. Early recognition and supportive interventions reduce mortality; however, severe toxic-phase disease carries high case-fatality rates, historically up to 50% among untreated severe cases. Post-recovery sequelae can include prolonged convalescence and persistent hepatic dysfunction in some survivors.

Epidemiology and history

Yellow fever has a documented history of sizable epidemics influencing exploration, colonial expansion and military campaigns, including outbreaks that affected Napoleon Bonaparte's forces in Saint-Domingue and impeded construction projects like the Panama Canal before control measures. The linkage of the virus to mosquitoes was elucidated through work by investigators such as Walter Reed, Carlos Finlay, and James Carroll which informed vector control and vaccine development. The 20th-century implementation of the 17D vaccine and public health campaigns conducted by organizations like the Rockefeller Foundation and Pasteur Institute reduced incidence in many urban centers, though sylvatic transmission persists in Amazon rainforest regions. Contemporary epidemiology shows periodic urban and sylvatic outbreaks concentrated in parts of West Africa and tropical South America, with population growth, urbanization, and global travel posing ongoing risks necessitating surveillance by agencies including the World Health Organization and Centers for Disease Control and Prevention.

Category:Viral hemorrhagic fevers