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Information on Dengue and Dengue Haemorrhagic fever

Introduction

Dengue is a mosquito-borne infection which in recent years has become a major international public health concern. Dengue is found in tropical and sub-tropical regions around the world, predominantly in urban and semi-urban areas.

Dengue haemorrhagic fever (DHF), a potentially lethal complication, was first recognized in the 1950s during the dengue epidemics in the Philippines and Thailand, but today DHF affects most Asian countries and has become a leading cause of hospitalization and death among children in several of them.

Prevalence

The global prevalence of dengue has grown dramatically in recent decades. The disease is now present in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, South-east Asia and the Western Pacific. South-east Asia and the Western Pacific are most seriously affected. Some 2500 million people — two fifths of the world's population — are now at risk from dengue. WHO currently estimates there may be 50 million cases of dengue infection worldwide every year.

Not only is the number of cases increasing as the disease is spreading to new areas, but explosive outbreaks are occurring. In 2001, Brazil reported over 390 000 cases including more than 670 cases of DHF.

• An estimated 500 000 cases of DHF require hospitalisation each year, of whom a very large proportion are children. At least 2.5% of cases die, although case fatality could be twice as high.
• Without proper treatment, DHF case fatality rates can exceed 20%. With modern intensive supportive therapy, such rates can be reduced to less than 1%.
  
  A rapid rise in urban populations is bringing ever greater numbers of people into contact with this vector, especially in areas that are favorable for mosquito breeding, e.g. where household water storage, garbage, old tires, flower pots are common and where solid waste disposal services are inadequate.

Transmission

The most important Mosquito vector is the predominantly urban species Aedes aegypti.

Dengue viruses are transmitted to humans through the bites of an infective female Aedes mosquitoe. Mosquitoes generally acquire the virus while feeding on the blood of an infected person. After virus incubation for 8-10 days, an infected mosquito is capable, during probing and blood feeding, of transmitting the virus, to susceptible individuals for the rest of its life.

Aedes mosquitoe is a morning feeder. Travelers should take insect bite protection if outdoors during the early morning hours.

Humans are the main amplifying host of the virus, although studies have shown that in some parts of the world monkeys may become infected and perhaps serve as a source of virus for uninfected mosquitoes. The virus circulates in the blood of infected humans for two to seven days, at approximately the same time as they have fever; Aedes mosquitoes may acquire the virus when they feed on an individual during this period.

Disease Characteristics

Dengue fever is a severe, flu-like illness that affects infants, young children and adults, but seldom causes death. Incubation period is 2 to 7 days.

The clinical features of dengue fever vary according to the age of the patient. Infants and young children may have fever with rash.

Older children and adults may have either a mild fever or the classical incapacitating disease with abrupt onset and high fever, severe headache, pain behind the eyes, severe muscle and joint pains, red eyes and a rash . A bleeding nose and bruising can also be seen in uncomplicated dengue.

Dengue haemorrhagic fever is a potentially deadly complication that is characterized by high fever, bleeding phenomena—often with enlargement of the liver—and in severe cases, circulatory failure. The illness commonly begins with a sudden rise in temperature accompanied by facial flush and other non-specific constitutional symptoms of dengue fever. The fever usually continues for two to seven days and can be as high as 40-41°C, possibly with febrile convulsions and bleeding phenomena.

In moderate DHF cases, all signs and symptoms abate after the fever subsides. In severe cases, the patient's condition may suddenly deteriorate after a few days of fever; the temperature drops, followed by signs of circulatory failure, and the patient may rapidly go into a critical state of shock and die within 12-24 hours, or quickly recover following appropriate volume replacement therapy.

Risk to Travelers

Travelers to dengue endemic area are at risk of contracting the disease. They should be counseled to use personal insect bite protection especially in the early morning and late afternoon when the mosquitoes feed.

Treatment

There is no specific treatment for dengue fever. However, careful clinical management by experienced physicians and nurses frequently saves the lives of DHF patients. With appropriate intensive supportive therapy, mortality may be reduced to less than 1%.

Maintenance of the circulating fluid volume is the central feature of DHF case management.

Immunization

None available.

Nonetheless, progress is being made in the development of vaccines that may protect against all four dengue viruses. Such products may become available for public health use within several years.

Prevention and Control

At present, the only method of controlling or preventing dengue and DHF is to combat the mosquitoes.
Travelers should know the feeding habits of the mosquito ( morning feeder) and should use DEET repellents, wear permethrin treated clothing and sleep in protected facilities would good screening.

In Asia and the Americas, Aedes aegypti breeds primarily in man-made containers like earthenware jars, metal drums and concrete cisterns used for domestic water storage, as well as discarded plastic food containers, used automobile tires and other items that collect rainwater. In Africa it also breeds extensively in natural habitats such as tree holes and leaf axils.

Mosquito control is implemented using environmental management and chemical methods. Proper solid waste disposal and improved water storage practices, including covering containers to prevent access by egg laying female mosquitoes are among methods that are encouraged through community-based program.

During outbreaks, emergency control measures may also include the application of insecticides as space sprays to kill adult mosquitoes using portable or truck-mounted machines or even aircraft. However, the killing effect is only transient, variable in its effectiveness because the aerosol droplets may not penetrate indoors to microhabitats where adult mosquitoes are sequestered, and the procedure is costly and operationally very demanding.