Yellow Fever
Like dengue fever, yellow fever is a prototype virus of the genus, Flavivirus (Becker et al. 2003). It is also considered one of the most lethal arboviruses, and occurs in Africa, and Central and South America (Goddard 2000).
Facts and Statistics:
· 90% of the world’s yellow fever cases occur in Africa (Service 2008).
· 20 - 50% case-fatality rates caused by yellow fever virus
· There are approximately 200,000 cases of yellow fever annually.
· Between 1990 and 1999, 11,297 cases of yellow fever were reported, with 2,648 resulting in death. Of these cases, 83% were in Africa.
(Resh & Carde 2009)
Facts and Statistics:
· 90% of the world’s yellow fever cases occur in Africa (Service 2008).
· 20 - 50% case-fatality rates caused by yellow fever virus
· There are approximately 200,000 cases of yellow fever annually.
· Between 1990 and 1999, 11,297 cases of yellow fever were reported, with 2,648 resulting in death. Of these cases, 83% were in Africa.
(Resh & Carde 2009)
How is Yellow Fever Transmitted?
Yellow fever virus is transmitted through the bite of a mosquito. There are three cycles that take place, leading to the spread of the virus. These are the sylvatic (or jungle) cycle, rural cycle, and urban cycle.
· Sylvatic Cycle:
o Yellow fever virus is transmitted between primates by tree-hole-breeding mosquitoes in the canopy of the forest. The main transmitters are Haemagogus and Sabethes, biting humans when they enter the forest, spreading the virus from monkeys to humans.
(Goddard 2000; Service 2008)
· Rural Cycle:
o When virulent monkeys are near the edges of the forest searching for food, they get bitten by a different mosquito such as Aedes bromeliae (major transmitter in Africa), which can then come in contact with humans, spreading the virus from monkeys to humans.
(Goddard 2000; Service 2008)
· Urban Cycle:
o Humans return to the village and, once virulent, domesticated vectors such as Aedes aegypti can spread the virus to the population.
(Goddard 2000; Service 2008)
Yellow fever virus is transmitted through the bite of a mosquito. There are three cycles that take place, leading to the spread of the virus. These are the sylvatic (or jungle) cycle, rural cycle, and urban cycle.
· Sylvatic Cycle:
o Yellow fever virus is transmitted between primates by tree-hole-breeding mosquitoes in the canopy of the forest. The main transmitters are Haemagogus and Sabethes, biting humans when they enter the forest, spreading the virus from monkeys to humans.
(Goddard 2000; Service 2008)
· Rural Cycle:
o When virulent monkeys are near the edges of the forest searching for food, they get bitten by a different mosquito such as Aedes bromeliae (major transmitter in Africa), which can then come in contact with humans, spreading the virus from monkeys to humans.
(Goddard 2000; Service 2008)
· Urban Cycle:
o Humans return to the village and, once virulent, domesticated vectors such as Aedes aegypti can spread the virus to the population.
(Goddard 2000; Service 2008)
In Aedes species, yellow fever virus can also be passed between mosquitoes transovarially (passed onto progeny), and via venereal transmission (during mating from congenitally infected males to females) (Service 2008).
The process of virus transmission from mosquito to human is shown at right (Click image for enlarged view). The mosquito’s viral cycle takes approximately 7 – 10 days, after which the salivary glands are infected and, for the rest of the mosquitoes life, any subsequent hosts will become infected when bitten (Resh & Carde 2009). |
Symptoms:
Yellow fever virus causes the disease, hemorrhagic fever (Barnett 2007). This disease can present a range of symptoms including jaundice (yellowish pigmentation of the skin associated with liver disease), hemorrhage from the nose and gums, and renal failure (Barnett 2007).
Yellow fever virus causes the disease, hemorrhagic fever (Barnett 2007). This disease can present a range of symptoms including jaundice (yellowish pigmentation of the skin associated with liver disease), hemorrhage from the nose and gums, and renal failure (Barnett 2007).
Other symptoms can also include:
· Fever · Chills · Headache · Backache |
· Myalgia · Prostration · Nausea · Vomiting |
(Goddard 2000; Barnett 2007)
Yellow Fever – Distribution Around the World:
The maps below illustrate the spread of yellow fever across the Americas and Africa.