What is Dengue Fever:- Dengue fever is a febrile illness caused by an RNA flavivirus that is spread by the bites of mosquitoes. Dengue hemorraghic fever is seen most often in individuals who were previously infected with simple dengue fever. Whereas dengue fever is rarely fatal, dengue hemorraghic fever is a severe disease that leads to death, in 5% cases. Dengue fever and dengue hemorraghic fever occur in Central America, South America, sub-Saharan Africa, Southern Asia, and the Western Pacific.

            Cases of dengue fever occur primarily in urban areas in the tropics. Estimates of the worldwide rate of dengue infection range from 20 million to 100 million cases each year, with an estimated 24,000 cases leading to mortality annually. Increases in urbanization, increases in international travel and trade, and decreases in public-health infrastructure in many countries have contributed to an alarming increase in the incidence of cases.

Signs and Symptoms of Dengue Fever:-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 up to 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 the body. Without prompt treatment, the blood vessels can collapse, causing shock, dengue shock syndrome and death. Dengue hemorraghic fever is seen most often in children younger than 15 years old. The time between the bite of a mosquito carrying dengue virus and the start of symptoms averages 4 to 6 days, with a range of 3 to 14 days. An infected person cannot spread the infection to other persons but can be a source of dengue virus for mosquitoes for about 6 days.

How do  People  Contract  Dengue Fever:- The dengue flavivirus occurs in four different serotypes, DEN-1, DEN-2, DEN-3, and DEN-4. Contracting one form of dengue fever provides lifelong immunity from that serotype, but not from the other serotypes. Humans contract dengue fever from bites of infected female mosquitoes of the genus Aedes. Aedes aegyptiis the primary vector in most regions. When a female Aedes mosquito bites a person infected with dengue, the virus incubates in the insect’s body for 8-11 days, after which the mosquito can spread the disease to other humans for the remainder of the insect’s life span (15-65 days). Once the virus enters a human, it circulates in the bloodstream for 2 to 7 days, during which time the virus can be spread to other blood-feeding Aedes mosquitoes.

Aedes aegypti originated in Africa, where it relied on temporary puddles of rain water in which to breed. The species subsequently expanded through much of the tropics, spread by ships, and then perhaps also by airplanes. Today there are two subspecies. Aedes albopictus is originally the primary vector of dengue fever, and remains a major vector in Asia. This species has recently spread to Central America and the U.S., where it is a secondary vector of the disease. The Aegypti formosusis is primarily urban.  

Control and Treatment of  Dengue Fever:-

Vaccines:- The  tetravalent  vaccines that has been developed now at Mahidol University in Thailand, in association with the World Health Organization are effective against all four serotypes of dengue fever.  Such vaccine is currently undergoing clinical trials and will be available for distribution soon.

Treatment. Treatment of dengue fever and dengue hemorraghic fever involves treatment of symptoms. With dengue hemorraghic fever, intensive support therapy, especially replacement of lost fluid volume when plasma leaks from the circulatory system, is tremendously important. Support  therapy involving fluid replacement can reduce dengue hemorraghic fever mortality rates.  Accurate detection of dengue is now possible with IgM-capture ELISA serological tests. Surveillance is important so that public-health and mosquito-control agencies can be alerted and mobilized prior to the outbreak of epidemics. 

Vector Control. Control of Aedes  vectors can contribute significantly to reductions in dengue infection rates. A primary method of controlling Aedes populations is by depriving female Aedes of pools of water in which to lay eggs. Covering cisterns, barrels, jars, and other water storage vessels, as well as discarding old tires and modernizing waste-water and solid-waste treatment systems, could reduce Aedes populations considerably. Additional methods of control include voiding bodies of water to kill mosquito eggs with compounds such as household bleach, larviciding pools of water to kill larval mosquitoes, and adulticiding with aerosol canisters. Surface spraying and/or aerial spraying are also sometimes used in severe outbreaks.

            As with all insect-borne diseases, simple personal protection, such as wearing long sleeves, applying insect repellent, and avoiding locations with high vector densities, is also important. Because Aedes mosquitoes are active in the daytime, personal protection strategies differ somewhat from those for mosquitoes active in the night time.