Dengue fever is an infection spread by mosquitoes which causes a severe flu-like illness, and can lead to a potentially lethal complication called Dengue haemorrhagic fever.
Outbreaks of Dengue fever become far more common in recent decades and according to the World Health Organisation (WHO) as many as two fifths of the world's population are now at risk and Dengue fever has now become a major international public health concern, comparable to that of malaria.
Dengue is commonly found in tropical and sub-tropical climates worldwide, most often in urban and semi-urban areas and Dengue haemorrhagic fever, a potentially lethal complication, is one of the leading causes of serious illness and death among children in some Asian countries
Dengue fever epidemics were first reported in 1779-1780 in Asia, Africa, and North America but was first recognized during dengue epidemics in the 1950s in the Philippines and Thailand.
A pandemic of Dengue which began in Southeast Asia after World War II, has now spread around the globe since that time and dengue haemorrhagic fever now affects most Asian countries and has become a leading cause of hospitalization and death among children in the region.
Experts suggest that as many as 2.5 billion people are now at risk from dengue and the WHO currently estimates there may be 50 million dengue infections worldwide every year - the disease is now endemic in more than 100 countries in Africa, the Americas, the eastern Mediterranean, south-east Asia and the western Pacific - before 1970 only nine countries had experienced Dengue haemorrhagic fever epidemics, a number that had increased more than four-fold by 1995.
In 2007 alone, there were more than 890,000 reported cases of Dengue in the Americas, of which 26,000 cases were Dengue haemorrhagic fever but south-east Asia and the western Pacific are the most seriously affected.
Experts say not only are the number of cases increasing as the disease spreads to new areas, explosive outbreaks are occurring - in 2007, Venezuela reported over 80,000 cases, including more than 6,000 cases of dengue haemorrhagic fever.
The evidence suggests that Dengue fever has been around on three continents for more than 200 years but during most of this time it was considered a mild, nonfatal disease of visitors to the tropics.
Dengue and Dengue Hemorrhagic Fever Types
There are four distinct, but closely related, viruses that cause Dengue and while recovery from infection by one provides lifelong immunity against that particular virus, it confers only partial and transient protection against subsequent infection by the other three viruses.
People living in a Dengue-endemic areas can have more than one Dengue infection during their lifetime and experts believe that sequential infection increases the risk of developing Dengue haemorrhagic fever.
Dengue and Dengue hemorrhagic fever are caused by the virus serotypes DEN-1, DEN-2, DEN-3, and DEN-4) and the four different dengue serotypes are maintained in a cycle that involves humans and infective female Aedes mosquitoes, the most common Aedes species, the Aedes aegypti is however the main culprit in spreading the virus which is a domestic, day-biting mosquito that prefers to feed on humans.
Dengue fever infections can result in a wide range of clinical illness ranging from a nonspecific viral infections to severe and fatal haemorrhagic disease.
This 2006 photograph depicted a female Aedes aegypti mosquito while she was in the process of acquiring a blood meal from her human host. The feeding apparatus consisted of a sharp, orange-colored “fascicle” that was covered in a soft, pliant sheath called the "labellum” while not feeding. The labellum was shown here retracted as the sharp "stylets" contained within pierced the host's skin surface, thereby, allowing the insect to obtain its blood meal. The orange color of the fascicle was due to the red color of the blood as it migrated up the thin, sharp translucent tube. Note the distended abdominal exoskeleton, which being translucent, allowed the color of the ingested blood meal to be visible.
The first reported epidemics of Dengue (DF) and Dengue haemorrhagic fever (DHF) occurred in 1779-1780 in Asia, Africa, and North America. The near simultaneous occurrence of outbreaks on three continents indicates that these viruses and their mosquito vector have had a worldwide distribution in the tropics for more than 200 years. During most of this time, DF was considered a mild, nonfatal disease of visitors to the tropics. Generally, there were long intervals (10-40 years) between major epidemics, mainly because the introduction of a new serotype in a susceptible population occurred only if viruses and their mosquito vector, primarily the Aedes aegypti mosquito, could survive the slow transport between population centers by sailing vessels.