Dengue haemorrhagic fever is dengue fever with haemorrhagic (bleeding) symptoms. It causes internal bleeding, capillary leakage, haemorrhagic petechial skin rashes, coma and shock. It is a severe form of dengue fever which may be associated with certain strains of the virus or may be related to the age or immune status of the individual infected. The virus is transmitted to man by the bite of an infected Aedes mosquito. The first infection is usually mild, but exposure to the virus tricks the immune system so that true resistance is not built up to the disease; indeed one becomes more susceptible.
Dengue haemorrhagic fever is common in urban India and Southeast Asia, and is one of Asia's most prevalent childhood diseases. A 5 year long outbreak started in Bangkok in 1958, killing 694 of 10,367 infected people. From 1989 to 1994, the incidence of dengue fever increased sixtyfold in Latin America, and there were 700 cases in Mexico in 1995. It occurs in epidemics, frequently among city dwellers. Between 10 and 15% of those infected die. DHF is more common in people less than 15 years of age; 10 is the average age of sufferers. DHF also commonly affects people having their second dengue infection.
Any semi-permanent large congregation of people without adequate shelter in a climate where mosquitoes can breed increases the risk of dengue fever, such as large city slum inhabitants and people in refugee camps. Although dengue fever has been reported in some international travellers, in general there is a low risk of DHF in tourists returning to the developed world. Prevention is key, because there is no specific therapy for dengue fever.