DF occurs in all tropical and some sub-tropical areas of the world, usually in an urban setting. Before 1970 only nine countries had experienced DF, by 1995 this had increased four fold. Today 2,5 billion people worldwide live in areas that are at risk of infection. Humans contract the disease when bitten by an infected female Aedes mosquito.
Mosquitoes remain infected all their lives and can in turn pass on infectivity to their eggs.
In some parts of the world it has been seen that monkeys are also able to pass on the infection to mosquitoes. After a bite from an infected Aedes mosquito, the virus circulates in the blood for 2-7 days, causing a feverish illness with headache and muscle pains similar to flu. Sometimes presents with a rash. Endemicity is high in Central America, as well as in African countries such as Mauritania around to Nigeria, with patches around the Egypt and the Sudan border. In Asia DF is endemic in Pakistan, Southern China and through to the North West area of Australia.