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Dengue Hemorrhagic Fever

Dengue Hemorrhagic Fever

Dengue fever is a flu-like illness spread by the bite of an infected mosquito. Dengue hemorrhagic fever is a severe, often fatal, complication of dengue fever. Dengue is spread by the bite of an Aedes mosquito. The mosquito transmits the disease by biting an infected person and then biting someone else.

Dengue viruses occur in most tropical areas of the world. Dengue is common in Africa, Asia, the Pacific, Australia and the Americas. It is widespread in the Caribbean basin. Dengue is most common in cities, but can be found in rural areas. It is rarely found in mountainous areas above 4000 feet. The mosquitoes that transmit dengue live among humans and breed in discarded tires, flowerpots, old oil drums and water storage containers close to human dwellings. Unlike the mosquitoes that cause malaria, dengue mosquitoes bite during the day.

Dengue and dengue hemorrhagic fever are caused by any of the dengue family of viruses. Infection with one virus does not protect a person against infection with another. Dengue fever usually starts suddenly with a high fever, rash, severe headache pain behind the eyes, and muscle and joint pain. The severity of the joint pain has given dengue the name “break bone fever.” Nausea, vomiting and loss of appetite are common.

A rash usually appears 3 to 4 days after the start of the fever. The illness can last upto 10 days, but complete recovery can take as long as a month. Older children and adults are usually sicker than young children. Most dengue infections result in relatively mild illness, but some can progress to dengue hemorrhagic fever. With dengue hemorrhagic fever, the blood vessels start to leak and cause bleeding from the nose, mouth, and gums. Bruising can be a sign of bleeding inside a body. Without prompt treatment, the blood vessels can collapse causing shock (dengue shock syndrome). Dengue hemorrhagic fever is fatal in about 5 percent of cases, mostly among children and young adults.

Dengue is diagnosed by a blood test. There is no specific treatment for dengue. Persons with dengue fever should rest and drink plenty of fluids. They should be kept away from mosquitoes for the protection of others. Dengue hemorrhagic fever is treated by replacing lost fluids. Some patients need transfusions to control bleeding. Vaccine development for dengue and DHF is difficult because any of four different viruses may cause disease, and because protection against only one or two dengue viruses could actually increase the risk of more serious disease. 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.

At present, the only method of controlling or preventing dengue and DHF is to combat the vector mosquitoes.

In Asia and Americas, Aedes mosquito 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 tyres and other items that collect rainwater. In Africa, it also breeds extensively in natural habitats such as tree holes and leaf axils.

In recent years, Aedes albopictus, a secondary dengue vector in Asia, has become established in: the United States, several Latin American and Caribbean countries, in parts of Europe and in one African country. The rapid geographic spread of this species has been largely attributed to the international trade in used tyres.

Vector 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 laying female mosquitoes are among methods that are encouraged through community-based programmes.

The application of appropriate insecticides to larval habitats, particularly those which are considered useful by the householders, e.g water storage vessels, prevent mosquito breeding for several weeks but must be re-applied periodically. Small, mosquito-eating fish and copepods (tiny crustaceans) have also been used with some success. 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 microhabits where adult mosquitoes are sequestered, and the procedure is costly and operationally very demanding. Regular monitoring of the vectors susceptibility to the most widely used insecticides is necessary to ensure the appropriate choice of chemicals. Active monitoring and surveillance of the natural mosquito population should accompany control efforts in order to determine the impact of the programme.

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