Yellow fever

Disease Description (Causes and Symptoms)

• Definition summary: Yellow fever is an acute viral infection caused by the yellow fever virus, a virus in the Flavivirus genus (an arbovirus), and it primarily occurs in Africa (sub-Saharan Africa) and South America through transmission by mosquitoes (e.g., Aedes species, among others).
• Pathophysiology summary: When a person is bitten by an infected mosquito, the virus enters the body and replicates in the mucosa and lymph nodes before spreading through the bloodstream and causing systemic viremia. It can invade organs such as the liver (hepatocytes), kidneys, and heart and cause coagulation abnormalities, potentially progressing to jaundice and a hemorrhagic course.
• Main symptoms: Incubation period of 3–6 days. Many infections are asymptomatic or mild. Mild cases: sudden fever, headache, muscle aches, nausea and vomiting, abdominal pain, and sometimes bradycardia (slow pulse). Some patients (approximately 10–20%) progress to the toxic phase (severe phase), developing high fever, severe headache, severe vomiting and abdominal pain, jaundice, bleeding (such as from the mucous membranes or gastrointestinal tract), kidney failure, liver failure, and other symptoms; the mortality rate may be high.

Treatment

• General principles: No specific antiviral drug that directly eliminates the yellow fever virus is currently commercially available, so treatment relies entirely on supportive care (symptomatic treatment).
• Acute-phase treatment
  • Hospitalization and intensive care: If severe findings are present (bleeding, shock, acute liver or kidney failure, decreased level of consciousness, etc.), immediate hospitalization and intensive care are required.
  • Fluid and hemodynamic management: Provide appropriate intravenous fluids for hypotension and use vasoactive agents if necessary.
  • Hemostasis and transfusion: If severe bleeding occurs, administration of blood products (fresh frozen plasma, platelets, etc.) may be considered.
  • In kidney failure: Hemodialysis (with low or no anticoagulation) may be used if necessary.
  • Fever and pain management: Acetaminophen is recommended (avoid NSAIDs and aspirin when there is a risk of bleeding).
  • Management of infectious complications: Use appropriate antibiotics if bacterial complications occur (based on clinical judgment).
• Preventive/public health measures
  • When a patient develops the disease, isolate the patient to prevent mosquito bites (block mosquito exposure) for at least 5 days after symptom onset — to prevent further transmission in the area.
  • In endemic areas, vaccination and mosquito control (insecticide use and elimination of breeding sites) are key preventive measures.
• Vaccine
  • A single dose of the live vaccine (17D series) produces immunity in most people. Protection develops within approximately 1 week after vaccination, and under WHO standards, most people are considered to have lifelong immunity. Additional vaccination may be recommended for some high-risk groups (immunocompromised people, laboratory workers, etc.) or according to the regulations of the relevant country.
  • Contraindications: Severe immunosuppression (e.g., currently receiving high-dose immunosuppressive therapy), known severe hypersensitivity to a live vaccine, etc. Pregnancy is generally a contraindication, but a risk–benefit assessment is necessary.
  • Rare severe vaccine adverse reactions: YEL-AVD (yellow fever vaccine-associated viscerotropic disease), YEL-AND (neurologic disease), etc. (Very rare).
• Other precautions: Because people suspected or confirmed to have yellow fever may have a tendency to bleed, avoid anticoagulants and NSAIDs and prepare for emergency response if necessary.

Checklist Before an Outpatient Visit (Including Items to Bring, Medical History Topics, and Example Questions)

• Items to bring
  • List of medications currently being taken (including prescription drugs, over-the-counter medicines, and supplements)
  • Past medical history (especially immunosuppressive diseases, transplants, cancer treatment, HIV status, and pregnancy status)
  • Recent travel history (country, region, length of stay, dates of entry and departure) and possible mosquito exposure
  • Time of symptom onset and course (date fever began, presence or absence of jaundice or bleeding symptoms, etc.)
  • Recent vaccination records (including yellow fever vaccination) and vaccination certificate (when traveling)
• Situations that should be reported to the outpatient clinic/emergency department in advance
  • Acute bleeding (vomiting blood, bloody stool, bleeding gums, etc.), changes in consciousness, persistent high fever, or symptoms of severe dehydration or hypotension
• Example medical history questions (for personal records)
  • When did the symptoms begin? How high was the fever?
  • Have you visited Africa (sub-Saharan Africa) or South America within the past 2 weeks?
  • Have you been vaccinated, or do you have a vaccination certificate?
  • What medications are you currently taking (especially anticoagulants, NSAIDs, or immunosuppressants)?

Examples of General Questions to Ask a Doctor

• What is the current status of this disease (assessment as mild vs. severe), and what is the prognosis?
• Is hospitalization or testing necessary? (e.g., blood tests, liver and kidney function tests, coagulation tests, PCR/antibody tests)
• Which medications may I take to relieve symptoms (such as antipyretics), and which medications should I avoid?
• If I have not been vaccinated, what are the vaccination recommendations and timing (the minimum interval before travel)?

Examples of Disease-Specific Questions

• I recently visited an affected endemic area. Would getting vaccinated now be meaningful for preventing infection? (Recommendations based on the time remaining before travel)
• If jaundice or bleeding symptoms appear, should I go to the emergency department immediately? What first aid should I provide in an emergency?

(Note: The information above is intended to supplement a doctor's consultation before and after medical care. If symptoms are severe or there are signs of an emergency, visit a medical facility immediately.)