Dengue and Dengue Hemorrhagic Fever
Dengue and Dengue Hemorrhagic Fever
If all of the infectious diseases of mankind were listed in order of incidence, dengue (DEN-gay) fever would clearly rank among the top ten—rivaling chickenpox, influenza, and urinary tract infection. Unfortunately, diseases that occur in tropical areas often acquire exotic names that are obscure and irrelevant to Western cultures. Thus, dengue is thought to derive from the Swahili dinga, meaning a seizure or cramp caused by evil spirits. Other diseases which bear such names are Chikungunya and O'nyong nyong.
Historically, Dengue appears to have originated in the Old World. The disease was first reported in the Caribbean-Latin American region in 1827 (Virgin Islands), presumably imported with African slaves. A second pandemic during 1848–1850 involved Cuba and New Orleans; and a third pandemic struck the region during 1979–1980.
The fact that dengue is not exclusively a “tropical” phenomenon is well illustrated by the American experience with the disease. Dengue was first reported in the United States in 1827, and caused a number of massive outbreaks in Louisiana, Hawaii (50,000 cases in 1903) and Texas (500,000 cases in 1922).
Dengue virus was first isolated in Africa during 1964 to 1968, in Nigeria; however, surveys suggest that the disease is common in certain areas of West Africa, and probably East Africa as well. It is suggested that many cases are misdiagnosed as malaria. Although the disease had been relatively rare in Australia, as many as 800 cases per year are now reported in that country.
The virus that causes dengue is one of 19 Flaviruses that infect humans. Flaviviruses account for 20 percent of all infectious virus species. Other Flaviviruses include the agents of Hepatitis C, West Nile fever, Japanese encephalitis, and yellow fever. Only 29 percent of virus diseases are acquired through the bites of mosquitoes; however, 53 percent of Flaviviruses are transmitted in this manner. A variety of mosquito species serve as vectors (transmitters) of Flaviviruses that cause dengue, most belonging to the species Aedes. Although dengue is almost exclusively a human disease, natural infection of monkeys has been reported in Asia.
In most cases, dengue is a self-limiting flulike illness. Two to fifteen days following the bite of a mosquito, patients experience fever with varying combinations of headache, retro-orbital (around the eyes) pain, myalgia (muscle aches), arthralgia (joint pain), rash, and leukopenia (low white cell count). Occasionally a “saddleback” fever pattern is evident, with a drop after a few days and rebounding within 24 hours. The pulse rate is often relatively slow in relation to the degree of fever. Conjunctival redness (red eyes) and sore throat may occur, often with enlargement of regional lymph nodes. A rash appears in as many as 50 percent of persons with dengue, either early in the illness with flushing or mottling, or between the second and sixth day as a florid red rash that spreads out from the center of the body. The rash fades after two to three days.
Symptoms generally resolve within 2 to 7 days, with no long term residual effects; however, significant depression may occur and persist for several months.
In a small percentage of persons, dengue fever may evolve into a severe and even life-threatening illness: dengue hemorrhagic fever (DHF) or dengue shock syndrome (DSS). Over 700,000 cases of DHF and 21,345 deaths were reported worldwide during 1956 to 1980; and over 1.2 million cases of DHF and 15,940 deaths during the five-year span from 1986 to 1990.
DHF is characterized by initial symptoms of dengue fever, in addition to bleeding tendencies such as petechiae (tiny reddish skin lesions associated with blood vessel injury) or ecchymoses (spontaneous bruises related to blood leakage). In some cases, overt bleeding occurs from the nose, mouth, stomach, colon, or other sites. The blood platelet count is low (less than 100,000 per cubic millimeter) and the red blood cell concentration increases as a result of fluid leakage from the circulatory system. DSS is characterized by the findings of DHF, in addition to signs of shock: low blood pressure, cold clammy skin, and mental obtundation (dullness).
Dengue is endemic (occurs naturally) in at least 115 countries, with over 2.5 billion persons at risk. Each year, an estimated 50 million to 100 million people are infected, most in Southeast Asia and Latin America. Approximately 30,000 to 50,000 persons die of dengue in any given year.
In recent years, most of the 100 or so cases reported annually in the U.S. have been acquired overseas; however, an outbreak of 122 cases was reported in Hawaii during 2001–2002, and 10–40 cases of local infection are reported in the southern border area of Texas each year.
Although few laboratories are equipped to cultivate the virus of dengue, a variety of rapid tests are available for diagnosis through identification of antibodies which appear during the course of illness. There is no specific drug therapy for dengue, and the development of effective vaccines has been hampered by the need to include all four viral types in any preparation, with a theoretical risk that the body might recognize the vaccine as dengue fever, and react with DHF/DSS when the person is later exposed to the native viruses.
Because the major damage in DHF/DSS is related to fluid loss, persons with these complications generally respond to intravenous fluid replacement of blood volume. Isolation precautions are not necessary; however, steps should be taken to exclude mosquitoes from patient treatment areas in endemic areas.
In recent years, Aedes albopictus (the Asian tiger mosquito) has gained prominence as a dengue vector in many parts of the world, largely as the result of dissemination of these insects in pools of water which accumulate in automobile tires transported on commercial ships. In addition, the spread of dengue fever is attributed to a rapid rise in the populations of cities in the developing world where dengue vectors thrive due to inadequate water storage and inadequate access to sanitation.
DHF and DSS appear to be related to immunological “over-reaction” in a person who develops dengue more than once in their lifetime. There are four sero-types (strains, or types) of Dengue virus, and sequential outbreaks in any given country may involve more than one serotype. Thus, if a person is infected with dengue type-1, and infected later in life (or during a later trip to a tropical area) with dengue type-2, his immunological experience from the first attack may prime him for a severe systemic (throughout the body) response to the new infection. As such, anyone who anticipates travel to an endemic country, or presents with signs suggestive of DHF/DSS, should be questioned regarding previous travel and experience with dengue.
In tropical cities, crowded conditions with little sanitation infrastructure can lead to an outbreak of dengue fever during the rainy season. In the following newspaper article, the author Adisti Sukma Sawitri describes the conditions of one neighborhood in west Jakarta, Indonesia, as it was in the midst of a dengue outbreak in early 2007 that eventually resulted in over 13,000 cases of dengue fever and 45 deaths. Sawitri is a journalist for the Jakarta Post.
Speilman, Andrew, and Michael D'Antonio. Mosquito: A Natural History of Our Most Persistent and Deadly Foe. New York: Hyperion, 2001.
Centers for Disease Control and Prevention. “Dengue Fever.” <http://www.cdc.gov/ncidod/dvbid/dengue/index.htm> (accessed May 25, 2007).
World Health Organization. “Dengue and Dengue Hemorrhagic Fever.” <http://www.who.int/mediacentre/factsheets/fs117/en/> (accessed May 25, 2007).
Stephen A. Berger