Before the discovery of the mode of transmission by Aedes aegypti mosquito in 1900 the Yellow fever was causing major epidemics in the Americas (North America and South America), Africa, and Europe. Despite the availability of an effective and safe vaccine for yellow fever, several hundred jungle yellow fever cases occur in South America every year, and thousands of jungle as well as urban cases of yellow fever occurs each year in Africa.

What is the causative agent of Yellow fever?

Yellow fever is caused by Yellow fever virus, a flavivirus. Yellow fever virus belongs to Flaviviridae family.

How yellow fever is transmitted?

Yellow fever is commonly transmitted by bite of Aedes aegypti mosquito. An urban cycle and a jungle cycle or sylvatic cycle (in Africa) of yellow fever virus exist, which involve Aedes mosquitoes and monkeys. Aedes aegypti mosquito is originally an African species, but has spread to other parts of the world.

What are the symptoms of yellow fever?

A 3 to 4 days of viremia (yellow fever virus in blood) a period called “intoxication” occurs. During “intoxication” phase the typical symptoms of Yellow Fever occurs such as characteristic jaundice, hemorrhages, black color vomit, anuria (no urine production or urination), and terminal delirium (may be due to extensive hepatic involvement). Yellow fever is a typical hemorrhagic fever, which commonly have liver necrosis.

What are the laboratory findings of Yellow fever?

WBC (white blood cell) count is generally normal or reduced in Yellow fever, but commonly high during late stages. Albuminuria (presence of albumin in urine) is generally present. Blood urea nitrogen (BUN) level rises proportionately to the failure of renal function in terminal or severe cases. Liver function tests are abnormal which ranges from modest elevations of AST levels in mild cases of Yellow fever to severe liver function abnormalities.

Treatment of Yellow Fever:

There is no effective antiviral agent available for treatment of yellow fever and the management of yellow fever is symptomatic. Symptomatic and general supportive treatment is given to yellow fever patient and complications treated as they arise.

Prevention of Yellow Fever:

The urban cycle of yellow fever can be prevented by the control of Aedes aegypti mosquito. But the jungle cycle or sylvatic cycle require vaccination to the locals as well as all the visitors to that particular area for control.

The Yellow Fever vaccine is generally a safe vaccine and reaction to vaccine is minimal. The immunity develop within 10 days and lasts for at least 10 years. Sometimes (rarely) allergic reaction to the vaccine may develop due to the egg protein present in the vaccine during manufacturing.

Rare, serious and occasionally fatal multisystem adverse reactions have been reported due to administration of yellow fever vaccine, particularly in the elderly patients. But the risk of contacting yellow fever (and number of deaths) among unvaccinated travelers is much higher than the number of deaths from vaccination, and a liberal vaccination policy for travelers to involved areas is recommended.

Yellow Fever vaccination has been reported to be associated with several cases of encephalitis in children of below 6 months of age. The present recommendation is to delay administration of Yellow fever vaccine until after 12 months of age, unless the risk of exposure is very high.

Pregnancy and Yellow Fever vaccine:

Pregnant women should receive Yellow Fever vaccine only if there is definite risk of exposure to yellow fever virus, although there no documented harmful effects of yellow fever vaccine on the fetus.

Yellow fever vaccination requirement for international travelers:

Yellow fever vaccination is mandatory for travel to many areas where yellow fever is endemic and where yellow fever is totally absent (for the fear of importing the disease to an area where the yellow fever is absent). For example yellow fever vaccination is mandatory for foreigners traveling to India (where yellow fever is absent but the vector mosquitos Aedes aegypti are abundant) to prevent introduction of yellow fever to India. Yellow fever vaccination is also mandatory for foreigner traveling to South and Centra America.