Dengue is a mosquito-borne viral infection of mostly tropical and subtropical urban and semiurban areas that causes fever. In the last half of the 20th century, incidence increased 50-fold. Dengue is endemic in over 100 countries although southeast Asia and the west Pacific are most severely affected. Two-fifths of the world’s population, including over 1 billion children, are exposed to the female Aedes mosquitoes that transmit the virus. There are approximately 50 million infections a year with 1 percent of infections developing into the potentially lethal dengue hemorrhagic fever (DHF). DHF has a global mortality rate of 5 percent. There is no treatment or vaccine for dengue, although with appropriate supportive therapy, mortality can be reduced to less than 1 percent. Although clearing an infection results in immunity against a particular serotype, there is only partial, transient cross-protection and an individual can be infected with another serotype. Sequential infection increases the probability of developing DHF.
The first reported cases and epidemics of dengue occurred in the 1600s. Dengue was initially considered a mild, nonfatal travelers’ disease. By 1845, global pandemics arose and continue today. During the 20th century, distribution and density of Aedes mosquitoes expanded because of human travel and trade. Rapid rise in urban population and unplanned urbanization led to inadequate solid waste disposal and unhygienic water storage, creating mosquito-breeding grounds. While eradication efforts began in the mid-1900s, they were discontinued, and reinfestation of Aedes mosquitoes occurred in larger distribution and density than previously. By 2005, dengue had a global distribution comparable to malaria.
The most common vector is the Aedes aegypti mosquito, which has global distribution, though Aedes albopictus, found in Africa, the Americas, and Europe, is also a vector. Aegypti is a daytime feeder that prefers humans and lays eggs preferentially in artificial containers such as used tires and water storage drums. Female Aedes mosquitoes acquire the virus by feeding on an infected human and shed the virus during subsequent feeding.
The dengue virus, a flavivirus, is the most widespread arthropod-borne virus, or arbovirus. Other mosquito-borne flavivirus infections include yellow fever and West Nile disease. All four dengue serotypes have a global distribution. There is a weeklong incubation period in mosquitoes prior to infectivity. For a week after a human is infected, the virus silently replicates in organs such as the thymus and then infects white blood cells. Viremia is detectable for approximately five days. Mosquitoes acquire the virus during this time. Illness will develop about two days after onset of viremia and continue for about a week. Dengue infection during pregnancy does not cause any congenital malformations. Dengue virus cannot be transmitted between humans. Dengue infections peak in winter.
Presentation is age dependent, with children experiencing a milder infection. The three categories of dengue fever, in increasing severity, are fever, dengue fever, and DHF. Fever is the most common presentation. Dengue fever also presents with headache, muscle and joint pain, nausea, vomiting, and rash. Weakness, malaise, and anorexia may persist for several weeks. Rarely, patients experience hemorrhagic manifestations including ruptured capillaries, bruising, and bleeding of gums and nose. DHF affects mostly children and is characterized by fever, hemorrhagic manifestations, low platelet count, and objective evidence of “leaky capillaries,” such as an elevated hematocrit or effusions. Without treatment, more than one in five patients dies. Fever in DHF patients can be as high as 41 degrees C (106 degrees F). The most severe form of DHF is dengue shock syndrome. After three to six days of fever, there is an abrupt temperature change, signs of circulatory failure, hypotensive shock and death within 12 to 24 hours.
Blood and urine tests showing elevated hematocrit, low albumin, or microscopic blood in urine are signs of dengue. Travel history can be important in diagnosis. Intensive supportive therapy focuses on maintaining circulating fluid volume. Treatment also includes rest, mosquito barriers, and fever and pain relief. Hospitalization is required when severe hemorrhagic manifestations or shock are present.
Because eradication is believed unattainable, efforts concentrate on controlling mosquito populations. Environmental management includes adequate solid waste disposal and improved water storage. Chemical management focuses on applying insecticides to larval habitats periodically. Insecticide spraying to kill adult mosquitoes has transient and variable effect because insecticide may not penetrate indoor habitats. Aedes mosquitoes are resistant to organochloride sprays and ultralow-volume fumigation is ineffective. Active surveillance of mosquito populations, habitats, and susceptibility is essential to prevention of dengue.
Hemorrhagic Fever; Infectious Diseases (General); Medical Entomology; Mosquito Bites; Viral Infections; Virology.
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