Yellow fever is a serious viral infection that is spread by a mosquito known as the Aedes aegypti mosquito. The causative agent is virus of the Flavivirus genus. Yellow fever mainly occurs in sub-Saharan Africa (countries to the south of the Sahara desert), South America and in parts of the Caribbean.
There are two forms of yellow fever: Urban and Jungle. Clinically and etiologically they are identical.
Urban yellow fever is an epidemic viral disease of humans transmitted from infected to susceptible persons by Aedes aegypti mosquitoes, which breed in domestic and peri domestic containers (e.g., water jars, barrels, drums, tires, or tin cans) and thus in close association with humans. In areas where Ae. aegypti has been eliminated or suppressed, urban yellow fever has disappeared. Urban yellow fever can be prevented by vaccinating human populations at risk for infection or by suppressing populations of Ae. aegypti mosquitoes so that they no longer perpetuate infection.
Jungle yellow fever can most effectively be prevented by vaccination of human populations at risk for exposure.
Incubation period of yellow fever is 3-6 days. Symptoms occur in 2 stages:
The first stage is also known as the ‘acute phase’, include:
A high temperature (fever) of 38ºC (100.4ºF) or above
Nausea and vomiting
Muscle pain, including backache
Loss of appetite
Second stage is more severe and is referred to as the ‘toxic phase’. The symptoms can include:
A recurrent fever
Jaundice – a yellow tinge to the skin and whites of the eyes caused by liver damage
Bleeding from the mouth, nose, eyes or stomach, leading to blood in your vomit and stools (faeces)
Yellow fever is caused by a type of virus known as a flavivirus. The infection is transmitted by the bite of certain mosquitoes. If one is travelling, developing risks of yellow fever will depend on:
Yellow fever is usually diagnosed based on the symptoms and the results of a blood test.
In blood tests: The blood test may also show a reduction in the number of infection-fighting white blood cells (leucopenia). This can occur because the yellow fever virus affects bone marrow (the spongy material at the centre of some bones that produces blood cells).
Laboratory diagnosis of yellow fever is generally accomplished by testing of serum to detect virus-specific IgM and neutralizing antibodies
Yellow fever can be prevented by taking vaccination against it. A single injection of yellow fever vaccine given subcutaneously provides immunity to 100% of its recipients. The vaccine provides immunity only after 10 days of vaccination. It confers lifelong immunity to people residing in yellow fever endemic countries. However, booster dose is required every ten years by persons residing in non endemic countries. The vaccine is contraindicated in persons allergic to egg, hypersensitive to previous dose, pregnant females, children younger than 9 months of age or with compromised immune diseases. The vaccine can be accompanied with mild side effects like fever, soreness, redness or swelling where the shot was given. These side effects usually subside within a week.
The yellow fever vaccines are readily available at 27 government vaccination centers approved by Ministry of Health and Family Welfare (MOHFW). The vaccination against yellow fever should be given at least 10 days before travelling to an endemic area.