Journal of Tropical Diseases & Public Health

Yellow fever

Yellow fever is a viral hemorrhagic disease caused by the yellow fever virus (YFV), a member of the genus Flavivirus. It is primarily transmitted to humans through the bite of infected mosquitoes, particularly Aedes aegypti and Haemagogus species. Yellow fever is endemic in tropical regions of Africa and South America and is characterized by fever, chills, loss of appetite, and muscle pain, followed by more severe symptoms in some cases.

Epidemiology

• Geographic Distribution: Yellow fever is endemic in parts of sub-Saharan Africa and tropical South America. It occurs in urban areas and rural regions, where the mosquito vectors are present.
• Incidence: According to the World Health Organization (WHO), there are an estimated 200,000 cases of yellow fever globally each year, with about 30,000 deaths.
• Outbreaks: Yellow fever outbreaks can occur, particularly in unvaccinated populations, and can lead to high mortality rates.

Transmission

• Mosquito Vectors: The primary mode of transmission is through bites from infected mosquitoes. Urban yellow fever is mainly transmitted by Aedes aegypti, while jungle yellow fever is transmitted by Haemagogus mosquitoes.
• Human Reservoir: Humans are the primary host for the virus in urban settings, while in rural settings, non-human primates can serve as reservoirs.
• Person-to-Person Transmission: Yellow fever is not transmitted directly from person to person but can occur through the mosquito vector.

Symptoms

Symptoms of yellow fever typically appear 3 to 6 days after infection and can range from mild to severe. The disease progresses through two phases:

• Initial Phase:
  • Fever
  • Chills
  • Loss of appetite
  • Muscle pain
  • Headache
  • Nausea and vomiting

• Toxic Phase (occurs in about 15% of cases):
  • Reoccurrence of fever
  • Abdominal pain
  • Liver damage, leading to jaundice (yellowing of the skin and eyes)
  • Bleeding (e.g., nosebleeds, gastrointestinal bleeding)
  • Organ failure, particularly liver and kidney failure

Diagnosis

• Clinical Evaluation: Diagnosis is based on clinical symptoms, history of travel to endemic areas, and exposure to mosquito bites.
• Laboratory Tests:
  • Serology: Detection of yellow fever-specific IgM antibodies in the blood.
  • PCR (Polymerase Chain Reaction): Detection of viral RNA in blood or tissue samples during the acute phase of illness.
  • Virus Isolation: In some cases, the virus can be isolated from blood or tissues.

Treatment

• Supportive Care: There is no specific antiviral treatment for yellow fever. Management focuses on supportive care, including:
  • Hydration
  • Pain relief (using acetaminophen, avoiding aspirin and NSAIDs due to bleeding risk)
  • Treatment of symptoms and complications as they arise

Prevention

• Vaccination: The yellow fever vaccine is safe and effective, providing immunity for 10 years or longer. Vaccination is recommended for individuals living in or traveling to endemic areas.
• Preventive Measures:
  • Mosquito control strategies, including the use of insect repellent, mosquito nets, and indoor spraying.
  • Public health initiatives to reduce mosquito breeding sites.

Global Health Implications

• International Travel: Some countries require proof of yellow fever vaccination for travelers coming from endemic areas. This is part of the International Health Regulations.
• Outbreak Response: Timely vaccination campaigns and vector control measures are crucial in controlling outbreaks and preventing the spread of the disease.

Prognosis

• Morbidity and Mortality: The case fatality rate for severe yellow fever can range from 20% to 50%, especially among unvaccinated individuals and those with pre-existing health conditions.
• Recovery: Most patients who recover from yellow fever have long-lasting immunity. However, severe cases can lead to significant long-term health issues, including liver damage.