Mosquito-borne haemorrhagic fever

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 first emerged in South and North America in the 1950's, then was absent for several decades, and in 1999 is now emerging again. After eradication efforts in Asia in the 1800s, dengue fever re-emerged in a slightly new form in the Philippines in the 1950s.

Dengue fever had been eradicated after the 1950s from the Americas with pesticides and the elimination of sources of standing water. In the late 1980s, efforts to eradicate the carrier mosquito diminished while the Latin American population increased along with poverty and urbanization, and so dengue fever has erupted again.

After 1985, there was further concern about dengue fever in North America because a potential new carrier, the Asian tiger mosquito Aedes albopictus, was been found in the USA. It can withstand cold and is a ravenous biter.

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.