Yellow Fever Flashcards
(25 cards)
What’s the causative agen for yellow fever? And family?
Major mode of transmission
Yellow Fever (YF) Overview
- Causative Agent: Yellow fever virus (Flavivirus, RNA virus)
- Vector: Aedes mosquitoes (mainly Aedes aegypti)
- Reservoirs: Humans and monkeys
- Transmission: Mosquito bite
- Risk Areas: Tropical and subtropical regions of South America and Sub-Saharan Africa
- At-Risk Group: Unvaccinated individuals in endemic areas
- Mortality (severe cases): 20–50%
Historical Highlights
- Origin: Africa
- First outbreak: 1648 in the New World
- Introduced via: Slave-trading ships carrying infected mosquitoes
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Major outbreaks:
- 1793, Philadelphia: 10% of city died
- 1878, Mississippi Valley: \~100,000 cases
When was vaccine breakthrough made?
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Vaccine breakthrough: 1930s by Max Theiler (17D vaccine)
- Nobel Prize: 1950
- Vaccine usage: Still incomplete in endemic regions ➡️ periodic outbreaks
There are how many genotype of this virus?
Which is found in Nigeria?
Epidemiology
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Genotypes: 7 total
- 5 in Africa: Angola, Central Africa, East Africa, West Africa I & II
- West Africa Genotype I: Found in Nigeria — highly virulent
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Seasonal Pattern:
- South America: Jan–Mar (peak rainfall & humidity)
- Africa: Late rainy to early dry season.
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WHO Data:
- 84,000–170,000 severe cases yearly in Africa
- 29,000–60,000 deaths
Yellow Fever in Nigeria
- Among 47 high-risk African countries
- Vaccine introduced: 2004 via routine immunization
- Problem: Low coverage ➡️ accumulation of susceptibles ➡️ outbreaks
2020 Outbreak (Nigeria)
- Reported: Nov 1, 2, 8 by Delta, Enugu, and Bauchi States
- Demographics: Mostly males, 1–55 years
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Symptoms:
- Fever, jaundice, vomiting (± blood), abdominal pain, epistaxis, hematuria, convulsion, unconsciousness
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Response:
- Nov 7: National Yellow Fever Emergency Operations Centre (EOC) activated
Outbreak Data (as of Nov 18, 2020)
State Suspected Confirmed Deaths
Bauchi | 89 | 8 | 8
Delta | 162 | 8 | 67
Enugu | 141 | 19 |75
Benue | 28 | 3 | 22
What are the Transmission Cycles of Yellow Fever?
Transmission Cycles of Yellow Fever
- Sylvatic (Jungle) Cycle
- Occurs: Tropical rainforests
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Vector:
- Haemagogus (South America)
- Aedes africanus (Africa)
- Reservoir: Monkeys
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How it spreads:
- Infected monkeys ➡️ forest mosquitoes → humans who enter forest
- Intermediate Cycle (Africa only)
- Occurs: Humid/semi-humid savannahs
- Vector: Semi-domestic mosquitoes
- Reservoir: Both monkeys and humans
- Features: Small outbreaks in rural communities
- Urban Cycle
- Occurs: Densely populated areas
- Vector: Aedes aegypti
- Transmission: Infected person from jungle/savannah introduces virus to urban population ➡️ epidemic
What’s the family and genus of yellow fever? And it’s related viruses
Virology of Yellow Fever Virus (YFV)
- Family: Flaviviridae
- Genus: Flavivirus (“flavus” = yellow in Latin)
- Related viruses: Dengue, Japanese Encephalitis, Tick-borne encephalitis
What is the **Structure of YFV **
YFV Structure
- Size: \~50 nm
- Capsid: Icosahedral
- Envelope: Yes
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Surface Proteins:
- M, E glycoproteins
- E protein: mediates host cell entry, fusion, and antibody neutralization
Genome
- Type: ssRNA (+) strand, infectious
- Size: \~11 kb
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Encodes:
- Structural: C, M, E
- Non-structural: NS1 to NS5
Stability
- Sensitive to: Heat, UV light, disinfectants, acidic pH
- Unstable outside host
What’s the Pathogenesis of Yellow Fever?
General pathology and organ specific pathology
Pathogenesis of Yellow Fever
- Entry: Bite from infected mosquito
- Initial replication: Regional lymph nodes
- Viraemia: Peaks between days 3–6
- Cytokines: ↑ TNF-α, IL-1RA, mild ↑ IL-6
- Systemic Spread: Liver, kidney, lungs, adrenal gland, spleen, bone marrow
Pathology
General Findings
- Widespread hemorrhages: Skin, mucosa, GI tract
- Hematemesis: From gastric mucosa erosion + petechial hemorrhage
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Bleeding Diathesis: Due to:
- ↓ clotting factors (liver failure)
- Thrombocytopenia
- Endothelial + platelet dysfunction
- DIC (Disseminated Intravascular Coagulation)
Organ-Specific Pathology
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Liver:
- Lobular necrosis
- Glycogen depletion
- Fatty change (steatosis)
- Councilman bodies (eosinophilic apoptotic cells)
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Kidneys:
- Acute tubular necrosis
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CNS:
- Cerebral oedema
- Hemorrhages
What’s the incubation period of yellow fever?
How’s the onset?
Spectrum:
Ranges from:
- Mild febrile illness
- To severe hemorrhagic fever (fatal in up to 50% of severe cases)
Clinical Features of Yellow Fever
- Incubation period: 3–6 days
- Asymptomatic cases: 5–50%
- Onset: Abrupt
What are the clinical features of yellow fever?
Three Classic Phases:
- Period of Infection
- Features: Fever, Faget sign (fever + bradycardia), chills, malaise, headache, flushing, nausea, dizziness
- Viraemia present — patient can infect mosquitoes
- Duration: Few days
- Period of Remission
- Features: Temporary improvement, fever subsides
- Duration: 2–48 hours
- May lead to full recovery or progress to next phase
- Period of Intoxication (15% of cases)
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Features:
- Return of high fever
- Nausea, vomiting
- Epigastric and lumbosacral pain
- Jaundice, renal failure, bleeding
- No viraemia
- Death: 7–10 days after symptom onset
Recovery:
- Convalescence: Prolonged fatigue and weakness for weeks
- Immunity: Lifelong after infection (due to neutralizing antibodies)
What are the possible complications of yellow fever?
And differential diagnosis?
Complications
- Bacterial superinfections: Pneumonia, sepsis
- Cardiac: Myocarditis, arrhythmias, heart failure
Differential Diagnosis
Consider in any patient with:
- Fever + jaundice + bleeding tendency
Infectious causes:
- Malaria
- Typhoid fever
- Dengue fever
- Viral hepatitis
- Lassa fever
- Marburg virus
- Ebola virus
- Hantavirus
- Leptospirosis
- Influenza
Non-infectious causes:
- Surgical/obstructive jaundice
- Toxic hepatitis
What are the Laboratory Diagnosis of Yellow Fever (YF)?
Direct Detection
- RT-PCR: Detects viral RNA
- Best within first 10 days of illness
- Viral culture: Samples from week 1
- Antigen detection: In tissue samples
- Immunohistochemistry: Post-mortem tissues for YF Ag
Serology (ELISA)
- IgM and IgG:
- Sample ≥ 3 days after symptom onset
- Positive = presumptive case
- PRNT (Plaque Reduction Neutralization Test):
- Confirms neutralizing antibodies to YF virus
Ancillary Labs
- FBC:
- Leukopaenia
- Relative neutropenia
- Thrombocytopenia
- Clotting profile:
- Prolonged PT
- ⬇️ clotting factor levels
- LFT:
- ⬆️ AST > ALT
- ⬆️ Serum bilirubin
- Renal:
- Proteinuria
- ⬆️ BUN, creatinine
YF Testing Algorithm (Nigeria). How’s it done?
And reference labs in 9ja
- ELISA IgM
- Positive = Presumptive
- Indeterminate = Inconclusive
- Negative = Negative
- All presumptive/inconclusive ➡️ Sent to reference labs for RT-PCR within 3 days
Reference Labs (6 total)
- Abuja (2)
- Kaduna (1)
- Lagos (1)
- Enugu (1)
- Edo (1)
How’s Management of Yellow Fever done?
No specific antiviral. Supportive care only.
- Hospital admission
- IV fluids for rehydration
- Paracetamol for pain (avoid aspirin/NSAIDs)
- Ventilation for respiratory failure
- Dialysis for renal failure
- Transfusions for bleeding
Infection Prevention & Control (IPC)
- No human-to-human transmission
- Isolate for differential diagnoses
- Use mosquito nets to prevent spread
- Standard precautions mandatory
How’s yellow fever **Prevented and Controled? **
1. Vector Control
- Reduce mosquito breeding
- Insecticide use
2. Vaccination: 17D Live-Attenuated Vaccine
- >90% protected in 10 days
- \~99% protected in 30 days
- Single dose = lifelong immunity
- Part of EPI in endemic zones
Vector Control (Nigeria)
Entomologic Survey (NAVRC 2007–2014)
- Identified 9 Aedes species in 19 states + FCT
- States: Kwara, Kogi, Benue, Edo, Cross River, Rivers, Akwa Ibom, Delta, Anambra, Imo, Enugu, Abia, Ebonyi, Ondo, Kaduna, Kebbi, Katsina, Zamfara, Taraba
Control Measures
- Eliminate mosquito breeding sites around homes, clinics, worksites
- Empty/cover water containers
- Proper waste disposal
- Use mosquito nets
- Plant water-retaining crops away from homes
- Apply biological/chemical larvicides
Yellow Fever Vaccine (17D)
Routine Immunization
- Single dose = lifelong protection
- Given at _____ month (introduced in Nigeria in 2004)
Tell me what you can about supplementary immunization
9 months
Supplemental Immunization
- “Catch-up” doses for those who missed routine vaccination
Mass Vaccination Campaigns
- PMVC (Preventive): Age 9 months–44 years
- Targets \~85% of population
- RMVC (Reactive): Same age group
- Deployed after outbreak confirmation to rapidly boost immunity.
What can you say about the EYE Strategy?
EYE Strategy (Eliminating Yellow Fever Epidemics)
Background
- Developed in 2016 after YF outbreaks in Angola, DRC, Brazil
- Global strategy covering 2017–2026
Objectives
- Protect at-risk populations
- Prevent international spread
- Contain outbreaks quickly
Vision:
A world without yellow fever epidemics
Mission:
Coordinate global support to help countries prevent, detect, and respond to outbreaks
Goal:
Minimize suffering, loss, and spread via early detection and timely response
What’s the Outbreak Response at Health Care Facility for YF
Outbreak Response at Health Care Facility
- Detect & manage cases; report and collect samples
- Train HCWs for high suspicion index
- Preposition supplies for outbreak response
- Follow YF-specific guidance for surveillance and epidemic control
- Activate case management protocols
- Use standard case definitions for diagnosis and reporting
- Report to LGA Disease Surveillance and Notification Officer (DSNO)
- Conduct active case search + blood sampling
- Send samples to designated lab for confirmation.
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