Yellow Fever

Yellow fever virus is an RNA that belongs to the genus Flavivirus and is related to West Nile, St. Louis encephalitis, and Japanese encephalitis viruses. It is transmitted human-to-human via the domestic species of Aedes mosquitoes (Urban epidemics) or to humans from primate reservoir via a forest mosquito species (Sylvatic cycle). About 15% of infections progress to fever and jaundice. While only the minority of cases are severe, case fatality rate may be 25% to 50% among patients with syndrome of haemorrhage, jaundice, and renal disease. A small proportion of patients develop “toxic phase” with jaundice (yellowing of the skin and eyes, hence the name ‘yellow fever’), dark urine and abdominal pain with vomiting. Bleeding can occur from the mouth, nose, eyes or stomach and half of those die within 7 to 10 days.

Risk factor: Sporadic cases often linked to occupation or village location near woods or where monkeys are numerous, also non-vaccinated persons. Infection and disease can be prevented by vaccination. With a vaccine efficacy > 95% and duration of immunity is life time.

Case definition

Suspected case: Any person with acute onset of fever, with jaundice appearing within 14 days of onset of the first symptoms.

Probable case: A suspected case with one of the following:

Epidemiological link to a confirmed case or an outbreak
Positive post-mortem liver histopathology

Confirmed case: A probable case with one of the following:

Detection of YF-specific* IgM
Detection of four-fold increase in YF IgM and/or IgG antibody titres between acute and convalescent serum samples
Detection of YFV-specific* neutralizing antibodies

*YF-specific means that antibody tests (such as IgM or neutralizing antibody) for other prevalent flavivirus are negative. This testing should include at least IgM for Dengue and West Nile and may include other flavivirus depending on local epidemiology.

One of the following

Detection of YF virus genome in blood or other organs by PCR

Detection of yellow fever antigen in blood, liver or other organs by immunoassays. Isolation of the yellow fever virus

Laboratory Investigations

ELISA for the presence of yellow fever Specific IgM and IgG antibodies
Exclusion of Dengue, West Nile virus and other locally prevalent flavivirus will be necessary for the confirmation of yellow fever
PCR, YF specific seroneutralization, virus isolation or histopathology

Management

Non-Pharmacological Treatment

No specific anti-viral treatment, supportive therapies are recommended. Good and early supportive treatment for dehydration, liver and kidney failure, and fever improves outcomes. Associated bacterial infections can be treated with antibiotics.

Prevention

Prevention and Control involve mosquito control and provision of Yellow Fever vaccine. The yellow fever vaccine is safe, affordable and a single dose provides life-long protection against yellow fever disease.

Indication of Yellow Fever Vaccination

Persons ≥ 9 months of age
Planning travel to or residence in an endemic area
Planning travel to a country with an entry requirement

Needs to be given ≥ 10 days prior to arrival in endemic area

Contraindications of Yellow Fever Vaccination

Infants aged less than 9 months;
Pregnant women – except during a yellow fever outbreak when the risk of infection is high;
People with severe allergies to egg protein; and
People with severe immunodeficiency due to symptomatic HIV/AIDS or other causes, or who have a thymus disorder

Public Health Control Measures

Identify all cases and provide clinical, epidemiological and laboratory evidences
Identify contacts, screen and test for confirmation
Educate the communities affected on mosquito control
Destroy known sources of standing water and any newly discovered sites for the presence of mosquito larvae
Surveillance of Mosquito by Mosquito control professionals