Yellow fever fact file

There are two types of yellow fever:-

• Jungle Yellow Fever also known as Sylvatic Yellow Fever occurs in tropical rainforests where monkeys, infected by sylvatic mosquitoes, pass the virus onto other mosquitoes that feed on them; these mosquitoes, in turn bite and infect humans entering the forest. This produces sporadic cases, the majority of which are often young men working in the forest e.g. logging.

• Urban Yellow Fever, the major cause of infection in humans, results in large explosive epidemics when travellers from rural areas introduce the virus into areas with high human population density. Domestic mosquitoes carry the virus from person to person. These outbreaks tend to spread outwards from one source to cover a wide area.

Both are viral illnesses, caused by the Yellow Fever Virus which belongs to the flavivirus group. It is spread by mosquitoes, most notably by the bite of the female Aedis Aegypti mosquito, which has unfortunately adapted well to living in villages, towns and cities, breeding in water storage containers, flower pots and discarded tyres found in residential areas. This particular mosquito is also found in Australia and many countries in Asia, areas which are currently uninfected, but could be at risk if visited by people carrying the disease.

The Yellow Fever Virus is an arbovirus and as such, has two characteristic phases, the first causing high fever as the virus invades the host cells, and then after a brief respite of a few days, the second when the body's immune system kicks in. It's this second phase that is most dangerous, as the antibodies generated can cause damage to the blood cells leading to bleeding as well as kidney and liver failure.