Makindo Medical Notes

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Body fluids contain the virus, and cross-contamination is possible, so strict isolation protocols are needed to prevent spread.

About Yellow Fever

• Yellow fever is a viral hemorrhagic fever caused by a Flavivirus and is spread by mosquito vectors.
• It is endemic among monkeys in regions of South America and West and Central Africa.
• Aedes aegypti mosquitoes primarily spread the virus among humans in urban settings, while Aedes Africanus in Africa and Haemagogus in the Americas spread it among primates in rural areas.

Aetiology

• Human infection occurs when infected mosquitoes come into contact with people.
• The virus is maintained in a rural cycle among primates and transmitted to humans in urban settings, creating dual transmission cycles.
• Yellow fever has a high impact in Sub-Saharan Africa and South America, but it is not seen in Asia.
• Humans can also act as viraemic hosts, enabling further mosquito-borne transmission.

Clinical Presentation

• Yellow fever symptoms begin 3-6 days post-infection following a mosquito bite, typically by day-feeding mosquitoes.
• Early symptoms include high fever, myalgia, red conjunctiva, and relative bradycardia (Faget’s sign).
• Jaundice often develops by day 2-3, with accompanying abdominal pain, lethargy, nausea, and vomiting.
• Severe cases may progress to disseminated intravascular coagulation (DIC), hemorrhage, shock, multiorgan failure, renal failure, and coma.

Differential Diagnosis

• Other conditions with similar presentations include:
  • Malaria
  • Typhoid fever
  • Viral hepatitis
  • Leptospirosis
  • Other viral hemorrhagic fevers
  • Aflatoxin poisoning

Investigations

• FBC: Elevated WCC may be seen in initial stages.
• Viral Isolation: Virus can be isolated from blood within the first 24 hours of symptoms.
• Liver Histology: Postmortem findings may reveal midzonal liver necrosis and Councilman bodies, a hallmark of yellow fever.
• Serology: IgM antibodies or a four-fold rise in IgG confirms recent infection.
• Coagulation Studies: May reveal DIC if hemorrhagic complications are present.

Management

• Supportive Care:
  • Administer IV fluids and plasma expanders to support circulation.
  • Transfusions may be needed to manage anemia and bleeding.
  • Consider renal replacement therapy for patients in renal failure.
• Infection Control: Strict isolation is essential to prevent cross-contamination from body fluids containing the virus. Mortality can reach up to 15% in severe cases.
• Prevention: Vaccination with a live attenuated vaccine is effective but contraindicated for immunosuppressed individuals.

References

• Mosquitoes and Their Control, Norbert Becker et al., Springer, 2010