In Pakistan, yellow Fever is managed by tropical medicines. Yellow fever is an acute viral hemorrhagic fever caused by a flavivirus transmitted by Aedes and Haemagogus mosquitoes in tropical Africa and South America. WHO estimates 84,000-170,000 severe cases and 29,000-60,000 deaths each year despite the availability of a highly effective single-dose live-attenuated vaccine licensed since 1937.
Yellow fever (ICD-10: A95) is an acute viral hemorrhagic fever caused by yellow fever virus (YFV), a single-stranded positive-sense RNA virus in the Flaviviridae family that is closely related to dengue, West Nile, and Zika viruses. The virus is transmitted to humans through bites of infected female mosquitoes in three distinct transmission cycles: jungle (sylvatic) yellow fever between forest mosquitoes (Haemagogus and Sabethes in the Americas; Aedes africanus in Africa) and non-human primates, with humans occasionally infected when entering the forest; intermediate (savannah) yellow fever in moist savannah regions of Africa where multiple Aedes species transmit virus between humans and monkeys in small villages; and urban yellow fever, in which Aedes aegypti transmits virus among humans in densely populated cities and produces large explosive outbreaks. The first phase of disease (period of infection) follows a 3-6 day incubation and consists of fever, headache, myalgia, backache, nausea, and conjunctival injection over 3-4 days. Roughly 85% of symptomatic patients recover at this point.
The key symptoms of Yellow Fever are: Sudden onset of fever above 39 °C with rigors, severe headache (often retro-orbital and frontal), and back pain 3-6 days after a mosquito bite in an endemic region., Severe muscle pain particularly in the back and legs, malaise, and prostration during the first 3-4 days (period of infection)., Conjunctival injection without exudate, facial flushing, and a tongue with red edges and white furred center — historical clinical descriptions., Relative bradycardia despite high fever (Faget's sign), an early clue that distinguishes yellow fever from many other tropical febrile illnesses., Apparent improvement on day 3-4 with defervescence and reduced symptoms — the brief remission., Return of fever, vomiting (sometimes with frank hematemesis — historic 'vomito negro' or 'black vomit'), and jaundice 24-48 hours after remission, marking the period of intoxication., Worsening jaundice and right-upper-quadrant abdominal pain from acute hepatic injury..
Diagnosis combines compatible clinical illness, exposure history (recent travel to or residence in a yellow fever transmission zone), and laboratory confirmation. Routine bloods in the toxic phase typically show leukopenia followed by neutrophilia, very high transaminases (AST often greater than ALT and rising into the thousands), conjugated and unconjugated hyperbilirubinemia, prolonged prothrombin time, thrombocytopenia, and rising creatinine. The specific diagnostic standard is detection of viral RNA by RT-PCR within the first 7-10 days of illness on blood or, in fatal cases, post-mortem liver tissue. Yellow fever IgM antibody is detectable from day 5-7 of illness and persists for months to years; cross-reactivity with other flaviviruses (dengue, Zika, Japanese encephalitis, West Nile) is significant and requires plaque-reduction neutralization testing (PRNT) at reference laboratories for confirmation. Vaccinated travellers retain IgG for life, so serology alone cannot diagnose acute infection in vaccinated patients without paired sera demonstrating a rise. Detection of yellow fever viral antigen (NS1) and immunohistochemistry of liver tissue (showing characteristic mid-zonal hepatocyte necrosis with Councilman bodies — eosinophilic apoptotic hepatocyte remnants) is a hallmark in post-mortem confirmation. Differential diagnosis is broad and includes other viral hemorrhagic fevers (Ebola, Lassa, Marburg, dengue, Crimean-Congo), severe malaria, leptospirosis, viral hepatitis (especially fulminant hepatitis A and E), severe sepsis, and toxic exposures. All suspected cases require notification to public-health authorities.
Outcome is determined primarily by whether the patient enters the toxic phase and by availability of intensive supportive care. Approximately 50% of infections are asymptomatic; among symptomatic patients, 85% recover after the period of infection alone. The 15% who progress to the toxic phase face 30-60% mortality — substantially worse in resource-limited settings without intensive care, blood-product support, and renal replacement therapy. Survivors of severe disease usually recover hepatic and renal function over weeks to months, although some retain residual liver-function abnormalities. There is no chronic carriage and no long-term viral persistence outside immune-privileged sites. Yellow fever vaccine produces lifelong protection in over 95% of recipients per WHO 2013 SAGE position, although a small minority of vaccinated travellers may benefit from boosters under specific circumstances (HIV infection, vaccination during pregnancy, post-hematopoietic stem-cell transplant). The 2017 WHO EYE strategy aims to vaccinate 1 billion people in 27 high-risk countries by 2026 through mass preventive campaigns, routine childhood immunization, and outbreak response.
Suspected yellow fever requires urgent evaluation by infectious disease and intensive care services. Severe disease (toxic phase) demands ICU-level care with hepatology and nephrology support. Travel medicine clinics deliver pre-travel vaccination and certification.
Find specialists →Mild yellow fever (period of infection only): full recovery within 1-2 weeks. Severe yellow fever survivors: hospital stay typically 2-3 weeks; full convalescence over 1-3 months. Liver function normalizes over 4-12 weeks; renal function over 4-8 weeks. Fatigue and reduced exercise tolerance can persist for several months after severe disease.
Bed rest during acute febrile illness. Gradual return to physical activity during convalescence over 2-6 weeks; severe disease with hepatic involvement may take 8-12 weeks for full recovery. Avoid contact sports until coagulopathy and thrombocytopenia resolve.
Pre-travel vaccination requires a designated yellow fever vaccination centre that can issue the International Certificate of Vaccination or Prophylaxis (yellow card). For suspected disease, seek care at a national reference laboratory or tertiary infectious disease unit.
Medically reviewed by AIHealz Medical Editorial Board · May 13, 2026
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