Makindo Medical Notes

Related Subjects: |Fever in a traveller |Malaria Falciparum |Malaria Non Falciparum |Viral Haemorrhagic Fevers (VHF) |Lassa fever |Dengue |Marburg virus disease |AIDS HIV |Yellow fever |Ebola Virus |Leptospirosis |Crimean-Congo haemorrhagic fever |African Trypanosomiasis (Sleeping sickness) |American Trypanosomiasis (Chagas Disease) |Incubation Periods |Notifiable Diseases UK

⚠️ Body fluids (blood, vomitus, urine) can contain the virus, so strict isolation protocols are required to prevent nosocomial spread. Standard precautions + vector control are essential.

🦠 About Yellow Fever

• Yellow fever is a viral haemorrhagic fever caused by a Flavivirus and transmitted by mosquitoes.
• Endemic in tropical South America and West/Central Africa, where both human and primate cycles exist.
• Aedes aegypti (urban cycle) spreads between humans; Aedes africanus in Africa and Haemagogus in the Americas maintain a sylvatic (jungle) cycle among primates.

📚 Aetiology

• Infection occurs via the bite of an infected mosquito.
• Dual transmission: jungle cycle (monkeys ↔ mosquitoes) and urban cycle (human ↔ mosquitoes).
• Despite global mosquito distribution, yellow fever is absent in Asia for reasons not fully understood (possibly herd immunity, mosquito competence, or ecological factors).
• Humans act as viraemic hosts, enabling epidemic spread.

🩺 Clinical Presentation

• Incubation: 3–6 days after the infective bite.
• Early symptoms: High fever, severe myalgia (“breakbone fever”), conjunctival injection, and relative bradycardia (Faget’s sign).
• Progression: Jaundice appears by day 2–3 with abdominal pain, nausea, vomiting, and lethargy.
• Severe disease: Can evolve into haemorrhage (epistaxis, GI bleed), DIC, shock, renal failure, coma, and multiorgan dysfunction.
• Mortality: Can reach 15% in severe cases despite supportive care.

🔍 Differential Diagnosis

• Malaria (especially falciparum)
• Typhoid fever
• Viral hepatitis
• Leptospirosis
• Other viral haemorrhagic fevers (e.g. Ebola, Lassa)
• Aflatoxin poisoning (rare)

🧪 Investigations

• FBC: Initial leukopenia and thrombocytopenia; later, raised transaminases.
• Viral isolation: Possible from blood within the first 24h of symptoms.
• Liver histology: Midzonal necrosis with Councilman bodies (acidophilic apoptotic hepatocytes) is characteristic.
• Serology: Detection of IgM or a four-fold IgG rise confirms recent infection.
• Coagulation studies: May reveal DIC in haemorrhagic cases.

💉 Management

• Supportive only: No specific antiviral therapy available.
• IV fluids and plasma expanders to maintain circulation.
• Transfusions for anaemia and coagulopathy; renal replacement therapy if renal failure develops.
• Infection control: Strict isolation + vector control to prevent spread.

🛡️ Prevention

• Vaccination: Live attenuated 17D vaccine provides long-lasting immunity; recommended for travellers to endemic areas.
• Contraindications: Immunosuppressed patients, infants <6 months, and pregnant women (unless high risk).
• Public health: International certificate of vaccination often required for travel to/from endemic regions.

📖 References

• Mosquitoes and Their Control, Norbert Becker et al., Springer, 2010
• WHO: Yellow Fever Fact Sheet
• CDC Yellow Book: Health Information for International Travel