By Neal Lineback and Mandy Lineback Gritzner,
Geography in the NewsTM and Maps.com
Reports of dengue fever were rare in Florida until 2009 when physicians began diagnosing cases around Key West in individuals who had not traveled outside the state. National Public Radio recently reported that, with mosquito season under way in 2011, health officials are on the alert for further spreading of this disease.
While the dengue fever problem in the United States is still relatively minor, the disease affects approximately 100 million people annually worldwide. In 2011, the World Health Organization (WHO) estimated that about 2.5 billion people, or 40 percent of the world’s population, live in areas where there is a risk of dengue transmission.
The Associated Press, however, recently reported that the World Health Organization (WHO) revised its estimates of the number of dengue fever worldwide to be almost four times greater than previous estimate. The new estimates are that over 390 million people may have the disease, but many have only minor symptoms. The significance of this is that there is a much larger reservoir of the virus undetected in many populations that can be the source of infection among the general population.
Dengue fever is caused by any one of four closely related viruses transmitted by mosquitoes. The viruses likely originated in monkeys in Africa and Southeast Asia between 100 and 800 years ago. When Aedes aegypti mosquitoes were unintentionally transported in cargo after World War II, dengue fever became a widespread disease.
The Aedes aegypti mosquito is a domestic day-biting mosquito that prefers to feed on humans. Probably even more so than the mosquito that causes malaria, aegypti is most closely associated with and adapted to human environments. Aedes aegypti is very comfortable laying its eggs in standing water inside or outside people’s homes, allowing it to thrive in urban environments. Poor urban areas, where people store water inside their houses or have no screens on windows or doors, are perfect breeding grounds for aegypti.
A dengue infection can range from a non-specific viral infection to severe hemorrhagic syndrome. Normal symptoms include fever, joint pain, headache and vomiting. Dengue hemorrhagic fever, on the other hand, is a potentially deadly complication that is characterized by very high fever, hemorrhagic phenomena (internal bleeding, often with enlargement of the liver), convulsions and, in severe cases, circulatory failure.
Physicians are finding that dengue fever is much more dangerous to persons contracting it multiple times. When a person is infected a second time with a different strain of the dengue virus, dengue hemorrhagic fever becomes much more likely.
The fatality rate in poor tropical countries from dengue fever is about 5 percent, but this can be reduced to 1 percent with proper medical care. Most fatal cases occur in children and young adults. There is no vaccine either to prevent or cure the disease.
Most dengue fever cases occur in urban and semi-urban areas in the tropics and subtropics. According to the U.S. Centers for Disease Control (CDC), dengue is endemic, that is, it occurs continuously, in at least 100 countries in Asia, the Pacific, the Americas, Africa and the Caribbean. Southeast Asia and the Western Pacific are the most seriously affected.
Normally, aegypti mosquito populations are highest in these countries during the rainy season. In addition, many areas are at risk for epidemic dengue, when large numbers of people become infected.
As dengue fever spreads to new areas, the total number of cases worldwide increases. In addition, the WHO reports that explosive epidemics are occurring. For example, Venezuela, a country without a history of serious previous dengue outbreaks, reported more than 80,000 cases in 2007, including more than 6,000 cases of dengue hemorrhagic fever.
In the United States, the southern part of the country is the most at risk for dengue fever. Dengue is endemic to northern Mexico and the Aedes aegypti mosquito is common in the southern United States, particularly in southern Texas, Florida and Hawaii. Furthermore, the American population has no immunity to the disease.
Fortunately most U.S. citizens are seldom exposed to the dengue fever viruses inside their homes because of air conditioning, screened windows and doors, use of insect repellents and relatively good indoor sanitation. Commercial pesticide use also has helped keep mosquitoes under some, but not total, control.
Attempts are being made to determine how dengue fever moves about geographically. A 2010 research effort by the U.S. Navy around Iquitos, Peru, in the Amazon Basin is an attempt to find how dengue fever returned after being eradicated in the region in the 1970s.
Totally eradicating dengue fever around the world will be impossible without a preventive vaccine, the eradication of the mosquito vector or a cure. Only science and medicine hold the keys to controlling this dogged disease.
And that is
Geography in the NewsTM
Co-authors are Neal Lineback, Appalachian State University Professor Emeritus of Geography, and Geographer Mandy Lineback Gritzner. University News Director Jane Nicholson serves as technical editor.
Sources: GITN #858 Dengue Fever: An Often Unrecognized Disease, Nov. 10, 2006; GITN #1101 Dengue Fever Spreads, July 8, 2011; http://www.npr.org/2011/06/10/137056759/tropical-disease-buzzes-back-into-u-s ; http://www.who.int/mediacentre/factsheets/fs117/en/; http://www.cdc.gov/dengue/; and The Associated Press, “Study estimates 390 million dengue cases,” Winston-Salem Journal, Apr. 8, 2013.
This is a revised version of GITN #1101 from Nov. 2006. Nearly 900 of the 1200, full-length weekly Geography in the News articles (with Spanish translations) are available in the K-12 online education resource Maps101.com, including maps and other supporting materials and critical thinking questions.