Yellow fever

Yellow fever, carried by mosquitoes, is endemic in sub-Saharan Africa and tropical South America. A biphasic illness with fever, headache, myalgia, conjunctival injection, bradycardia, and leukopenia is followed in a few hours to a few days by more severe symptoms.

CASES/YEAR
0 (US); 200,000 (Global)
CATEGORY
Arthropod-Borne
AGENT TYPE
Viruses
OTHER NAMES
ACUITY
Acute-Severe
INCUBATION
3-6 days; [CCDM]
INITIAL SYMPTOMS
A biphasic illness with fever, headache, myalgia, conjunctival injection, bradycardia, and leukopenia followed in a few hours to few days by high fever, backache, vomiting, abdominal pain, jaundice, bleeding diathesis, and albuminuria; [PPID, p. 2077]
PRECAUTIONS
Standard; Install screens in endemic areas. No person-to-person transmission; [ABX Guide]
COMMENTS
FINDINGS
Severity ranges from an unapparent infection to a 20%-50% case-fatality rate in some outbreaks. Most cases resolve after 5 days without hemorrhagic symptoms. [CCDM, p. 683] Yellow fever is biphasic with a flu-like illness for 3-4 days followed in 15% to 25% of cases by a fulminant illness with a case-fatality rate of 20% to 50%. In the second stage, complications may include jaundice, shock, bleeding diathesis, hepatorenal syndrome, cerebral edema, and myocarditis. [ID, p. 2110-11] Renal effects include albuminuria, hematuria, reduced output, and rising creatinine and BUN. Complications include bacterial pneumonia, parotitis, and sepsis. True encephalitis is rare. [Guerrant, p. 496-7]

EPIDEMIOLOGY:
No recent cases have been reported in North America or Europe. Urban outbreaks in the Americas occur occasionally with the most recent in Asuncion, Paraguay in 2008. Reservoirs are humans in urban areas and monkeys in forests. [CCDM, p. 684] The 3 transmission cycles are: (1) Sylvatic (jungle); (2) Intermediate (savannah); and (3) Urban. The disease is an occupational hazard for unimmunized young men working in the tropical forests of South America. Transmission could occur by needlestick or transfusion, given the high level of viremia in patients. From 1970 to 2015, only 11 cases of travelers (American & European) with yellow fever were reported. [CDC Travel, p. 377-8]

LABORATORY:
Jaundice, albuminuria, and hematemesis are seen in severe cases. Albuminuria (as high as 20g/L) occurs in 90% of patients. Thrombocytopenia and increased prothrombin time are associated with petechiae and mucosal bleeding. [Merck Manual, p. 1489] Albuminuria is a consistent finding that distinguishes the disease from other causes of hepatitis. Patients have seizures and coma in the late stages. [PPID, p. 2027-8] Hepatic and renal failure cause encephalopathy (cerebral edema), and this is reflected in the CSF findings (elevated protein without pleocytosis). [ID, p. 2111] In the three clinical stages (infection/remission/intoxication), leukopenia occurs in the first, and leukocytosis & thrombocytopenia occur in the third. [Guerrant, p. 496]
DIAGNOSTIC
Viral culture; Antigen detection by ELISA; RNA-PCR; IgM antibodies; Paired sera; [CCDM] Virus isolation and nucleic acid amplification become negative when symptoms become pronounced, so not to be used to rule out diagnosis; [CDC Travel]
SCOPE
Endemic in sub-Saharan Africa and tropical South America; See Maps 4-13 & 4-14 for countries with risk of transmission.); [CDC Travel]
SIGNS & SYMPTOMS
  • >fatigue, weakness
  • >fever
  • >fever, biphasic or relapsing
  • >myalgia
  • >relative bradycardia
  • E epistaxis
  • G abdominal pain
  • G blood in stool
  • G constipation
  • G hematemesis
  • G jaundice
  • G liver function test, abnormal
  • G nausea, vomiting
  • H leukocytosis
  • H leukopenia
  • H thrombocytopenia
  • N confusion, delirium
  • N headache
  • N lethargy
  • N seizure
  • O conjunctivitis, acute
  • S petechiae and ecchymoses
  • U hematuria
  • *acute renal failure
  • *bleeding tendency
  • *encephalitis
  • *hepatitis
  • *myocarditis
  • *parotitis
  • *pneumonia
  • *sepsis
  • *shock
  • *stupor, coma
ANTIMICROBIC

No

VACCINE

Yes

ENTRY
VECTOR
Mosquitoes
RESERVOIR
Monkeys, Human
RISK FACTORS
  • Fail to complete immunizations
  • Travel to endemic area
  • Victim--air release of infectious agents
  • Work in a medical or research lab
  • Work in forest in endemic areas of Central and South America
DRUG LINK
Merck Manual: Yellow Fever
REFERENCES FOR CASES/YEAR
1.
2. (Global) 200,000 cases and 30,000 deaths per year; [Fact sheets from WHO 2013]