Texas lifestyle limits transmission of dengue virus.Urban dengue dengue
or breakbone fever or dandy fever
Infectious, disabling mosquito-borne fever. Other symptoms include extreme joint pain and stiffness, intense pain behind the eyes, a return of fever after brief pause, and a characteristic rash. is common in most countries of the Americas, but has been rare in the United States for more than half a century. In 1999 we investigated an outbreak of the disease that affected Nuevo Laredo, Tamaulipas, Mexico, and Laredo, Texas, United States, contiguous cities that straddle In the stock and commodity markets, a strategy in options contracts consisting of an equal number of put options and call options on the same underlying share, index, or commodity future. the international border. The incidence of recent cases, indicated by immunoglobulin M immunoglobulin M
n. Abbr. IgM
The class of antibodies found in circulating body fluids and the first antibodies to appear in response to an initial exposure to an antigen. antibody serosurvey, was higher in Nuevo Laredo, although the vector, Aedes aegypti, was more abundant in Laredo. Environmental factors that affect contact with mosquitoes, such as air-conditioning and human behavior, appear to account for this paradox. We conclude that the low prevalence of dengue in the United States is primarily due to economic, rather than climatic, factors.
Outbreaks of mosquito-borne infection are commonly assumed to occur wherever competent vectors and a suitable climate exist, and that "global warming"--climate change caused by human activities--will cause these diseases to move to higher altitudes and latitudes. In many parts of the world, however, such diseases have become uncommon, despite an abundance of vectors and an ideal climate.
Denguelike illness was first noted in the New World as a major outbreak in Philadelphia in 1780 (1), and similar episodes occurred in the United States for more than 150 years. In 1922, the disease struck many major cities in the southern states, including an estimated 500,000 cases in Texas. Another widespread outbreak occurred in 1947-48 (2). In the past 50 years, however, autochthonous autochthonous /au·toch·tho·nous/ (aw-tok´thah-nus)
1. originating in the same area in which it is found.
2. denoting a tissue graft to a new site on the same individual. cases have been rare, despite an abundance of Aedes aegypti in the southeastern United States, and the arrival of millions of travelers from neighboring countries where the disease is endemic. From 1980 to 1999, only 64 locally acquired cases were confirmed in Texas, whereas 62,514 suspected cases were recorded in three adjoining Mexican states--Coahuila, Nuevo Leon, and Tamaulipas. In the same period, immigration authorities reported [less than or equal to] 70 million personal crossings from these states into Texas in a single year (3). Thus, the international border separates a dengue-endemic region from one in which the disease is rare.
Laredo, Texas, United States (population 200,000), and Nuevo Laredo, Taumalipas, Mexico (population 289,000), are essentially a single city (locally known as "los dos Laredos") divided by a small river, the Rio Grande (Figure). The rapid growth of this metropolitan area--70% in the past decade--is mainly due to massive cross-border traffic across three multilane mul·ti·lane
Having several lanes: a multilane highway.
Adj. 1. multilane - (of roads and highways) having two or more lanes for traffic bridges (Laredo Chamber of Commerce. Laredo, Texas; available from: URL URL
in full Uniform Resource Locator
Address of a resource on the Internet. The resource can be any type of file stored on a server, such as a Web page, a text file, a graphics file, or an application program. : http://www.laredochamber.com/contactinformation.htm). In the summer of 1999, toward the end of a local dengue outbreak, we conducted a seroepidemiologic survey to examine factors affecting dengue transmission on both sides of the border.
Households were selected by a modified version of the cluster survey of the World Health Organization Expanded Program on Immunization immunization: see immunity; vaccination. (4). First, we mapped the population of each census block in Laredo and in a major portion of Nuevo Laredo (Sector 1). In each city, 30 clusters were chosen from these census blocks by using a selection probability proportional to population. Four city blocks were randomly chosen from each of these clusters, and individual houses in one or more of those blocks were selected at random (where block maps were available) or systematically from a randomly chosen starting point. Blocks were sampled until 7-12 households had been enrolled from each cluster.
Of, relating to, or involving two nations. teams, each composed of an epidemiologist, a nurse, and an entomologist, conducted the surveys. A blood sample was obtained by fingerstick from a randomly selected resident (ages 18-65).  A short questionnaire solicited general household information (number of inhabitants
The game is based loosely on the concepts from SameGame. , type of construction, proximity to neighboring houses, number of bedrooms, presence and type of air-cooling system, and the presence and quality of window screens). Demographic data and travel histories of the blood donors were also recorded. Yards and patios were searched for Ae. aegypti breeding sites.
Serum samples were tested for anti-dengue immunoglobulin M (IgM) by IgM antibody-capture enzyme-linked immunosorbent assay enzyme-linked immunosorbent assay
Enzyme-linked immunosorbent assay (ELISA)
A diagnostic blood test used to screen patients for AIDS or other viruses. (MAC-ELISA), and for anti-dengue IgG by IgG-ELISA and mixed dengue antigens (5,6). Data were analyzed with SAS (1) (SAS Institute Inc., Cary, NC, www.sas.com) A software company that specializes in data warehousing and decision support software based on the SAS System. Founded in 1976, SAS is one of the world's largest privately held software companies. See SAS System. v.6.12 (SAS Institute, Inc., Cary, NC) and SAS-callable SUDAAN (Research Triangle Institute The Research Triangle Institute (RTI) is a non-profit research organization based in the Research Triangle Park (RTP) of North Carolina. RTI is the oldest tenant of this major research park, and the sister organization to the Research Triangle Foundation. , Research Triangle Park Research Triangle Park, research, business, medical, and educational complex situated in central North Carolina. It has an area of 6,900 acres (2,795 hectares) and is 8 × 2 mi (13 × 3 km) in size. Named for the triangle formed by Duke Univ. , NC) software. Risk factors for IgM and IgG seropositivity Seropositivity is the presence of a certain antibody in a blood sample. A patient with seropositivity for a particular antigen or agent is termed seropositive. were assessed by multivariable weighted logistic regression, accounting for stratification by country, clustering within each city, and different numbers of surveys per cluster. Backward selection of variables was used to create the final models. Variables were retained if statistically significant (p<0.05).
Surveys were completed in 622 households (309 in Laredo, 313 in Nuevo Laredo), and 516 persons (228 in Laredo, 288 in Nuevo Laredo) provided blood samples. IgM seropositivity (Table 1) was lower in Laredo (1.3%; 95% confidence interval confidence interval,
n a statistical device used to determine the range within which an acceptable datum would fall. Confidence intervals are usually expressed in percentages, typically 95% or 99%. [CI] 0 to 3%) than in Nuevo Laredo (16%; CI 12% to 20%). IgG seropositivity (Table 1) was also lower in Laredo (23%; CI 17% to 28% vs. 48%; C141% to 55%). Conversely, mosquito-infested containers were more abundant on the Texas side of the border: the Breteau Index (the number of infested in·fest
tr.v. in·fest·ed, in·fest·ing, in·fests
1. To inhabit or overrun in numbers or quantities large enough to be harmful, threatening, or obnoxious: containers per 100 houses) was 91 in Laredo versus 37 in Nuevo Laredo. Eighty-two percent of homes in Laredo had central or room air-conditioning versus 24% in Nuevo Laredo. In Laredo, evaporative coolers (a low-technology air-conditioning device that cools and humidifies air by drawing it from outdoors through a continually wetted screen) were less prevalent, a greater proportion of houses had intact screens, the average distance between houses was greater, and fewer persons lived in each house (Table 2).
Univariate analysis indicated a significant association between IgM seropositivity and five variables: absence of air-conditioning, fewer room air-conditioning units, the presence of an evaporative cooler, no travel outside the Laredo/Nuevo Laredo area, and shorter distances to neighboring houses (Table 3). IgG seropositivity was significantly associated with absence of central air-conditioning, fewer room air-conditioning units, smaller plot size, and a shorter distance to neighboring houses (Table 4).
On multivariate analysis multivariate analysis,
n a statistical approach used to evaluate multiple variables.
n a set of techniques used when variation in several variables has to be studied simultaneously. , backward selection of variables yielded two that remained significantly associated with IgM seropositivity: absence of air-conditioning (odds ratio [OR] 2.6; CI 1.2 to 5.6) and no history of travel beyond Laredo/Nuevo Laredo in the previous 3 months (OR 2.0; CI 1.0 to 4.0). IgG seropositivity was associated with absence of air-conditioning (OR 2.4; CI 1.5 to 4.0), a history of crossing the border during the previous 3 months (OR 1.8; CI 1.1 to 2.8), and a greater number of occupants per household (OR 1.1; CI 1.0 to 1.2). By using the calculated prevalence ratio of 2.6 as an estimate of the relative risk of dengue in houses without air-conditioning, the proportion of dengue infections attributable to lack of air-conditioning in Nuevo Laredo was 55%, i.e., 55% of cases of dengue in Nuevo Laredo would not have occurred if all households in Nuevo Laredo had air-conditioning.
Given the proximity of the two cities, the difference in transmission rates cannot be attributed to climate. Moreover, the mean daily temperature for August, the peak month of transmission, was 32.2[degrees]C (mean maximum 40.0[degrees]C; mean minimum 24.4[degrees]C), several degrees higher than the mean for the hottest months on Caribbean islands where dengue is common. Indeed, summer temperatures throughout the range of Ae. aegypti in the southern United States The Southern United States—commonly referred to as the American South, Dixie, or simply the South—constitutes a large distinctive region in the southeastern and south-central United States. are hotter than in many tropical regions where the disease is endemic.
Despite mosquito control campaigns on both sides of the border, Ae. aegypti infestation infestation /in·fes·ta·tion/ (-fes-ta´shun) parasitic attack or subsistence on the skin and/or its appendages, as by insects, mites, or ticks; sometimes used to denote parasitic invasion of the organs and tissues, as by helminths. rates in Laredo were remarkably high. The Breteau Index was on a par with that observed during major dengue epidemics in Puerto Rico (CDC See Control Data, century date change and Back Orifice.
CDC - Control Data Corporation , unpub. data). The House Index (the percentage of houses with at least one infested container) was 37%, seven times higher than the level (5%) equated with a "high risk" of dengue transmission by the World Health Organization (7). Thus, vector populations cannot account for the low rate of transmission on the Texas side of the border.
Ae. aegypti is closely associated with human habitation and readily enters buildings to feed and to rest during periods of inactivity (8). In this context, casual observation supported the association of lack of air-conditioning with dengue transmission. In Laredo, most shops, restaurants and other public places are air conditioned and have closed windows and self-closing doors, as do houses in residential areas, even in low income neighborhoods. By contrast, in Nuevo Laredo, many shops, bars, and restaurants are open to the street, and the windows and doors of houses are left open, particularly in the daytime. Thus, there is less opportunity for mosquito/human contact in Laredo than in the Mexican city.
More than 85% of all buildings in Texas are fully air conditioned (American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA; available from: URL: http://www.ashrae.org/). Indeed, air-conditioning is ubiquitous in many parts of the United States. To maximize heating/cooling efficiency, windows are usually fully glazed and are often kept permanently closed. Thus, most people spend much of their daily life sequestered se·ques·ter
v. se·ques·tered, se·ques·ter·ing, se·ques·ters
1. To cause to withdraw into seclusion.
2. To remove or set apart; segregate. See Synonyms at isolate.
3. in sealed buildings. Even if infected mosquitoes gain entry to such buildings, the artificially dry atmosphere lowers their survival rate, and the cool temperature extends the extrinsic incubation period extrinsic incubation period
The interval between the acquisition of an infectious agent by a vector and the vector's ability to transmit the agent to other susceptible vertebrate hosts. , reducing the likelihood of transmission. Presumably pre·sum·a·ble
That can be presumed or taken for granted; reasonable as a supposition: presumable causes of the disaster. , when denied access to humans, mosquitoes must seek other hosts. In Puerto Rico and Thailand, some Ae. aegypti feed on dogs, even when humans are readily accessible (9,10). In Laredo, we observed that large dogs were housed in outdoor kennels at many homes. Whether these animals are an important blood source for the species would be an interesting topic for future research.
The dollar cost of electricity is similar in Laredo and Nuevo Laredo, but income, as indicated by per capita [Latin, By the heads or polls.] A term used in the Descent and Distribution of the estate of one who dies without a will. It means to share and share alike according to the number of individuals. gross domestic product, is much higher in Texas than in Taumalipas (Table 5). The proportional cost of maintaining air-conditioning for an entire dengue season is therefore much higher for the average family in Mexico and is unaffordable un·af·ford·a·ble
Too expensive: medical care that has become unaffordable for many.
un for the majority. Thus, the ultimate determinant of dengue prevalence in this setting is socioeconomic rather than environmental.
It has frequently been stated that dengue, malaria, and other mosquito-borne diseases will become common in the United States as a result of global warming (11-14). Such predictions often refer to vectorial capacity, a simple model that incorporates the population density, biting frequency, and daily survival probability of the vector, and the extrinsic incubation period of the pathogen (15,16). Although the vectorial capacity model has proved useful for interpreting entomo-epidemiologic data, particularly for transmission of malaria (17), it does not incorporate factors like air-conditioning, use of evaporative coolers, and the behavior of mosquitoes and humans. If the current warming trend in world climates continues, air-conditioning may become even more prevalent in the United States, in which case, the probability of dengue transmission is likely to decrease. If the economy of Mexico continues to grow, the use of air-conditioners may gain momentum south of the border.
Table 1. Seroprevalence of anti-dengue immunoglobulin G (IgG) and IgM antibodies in Nuevo Laredo, Mexico, and Laredo, Texas, United States Nuevo Laredo Laredo Households 313 309 Serum samples 288 228 IgM prevalence 16% (12 to 20) (a) 1.3% (0 to 3) (a) IgG prevalence 48% (41 to 55) (a) 23% (17 to 28) (a) (a) Weighted point estimate and (95% confidence interval). Table 2. Selected housing and travel characteristics in Nuevo Laredo and Laredo residents Characteristic Nuevo Laredo Laredo Central air-conditioning 2% 36% Room air conditioner 23% 52% Evaporative cooler 29% 17% Screens on windows 54% 78% Intact window screens 36% 60% Mean no. occupants/residence 4.5 3.8 Mean distance to neighbors (m) 3.0 4.5 No travel outside Laredo/Nuevo Laredo area 70% 63% Crossed border within 3 months of survey 52% 43% Table 3. Risk factors associated with anti-dengue immunoglobulin M (IgM) seropositivity in Nuevo Laredo/Laredo residents, by univariate analysis Mean value for IgM Risk factor Prevalence ratio seropositive residents No air-conditioning 2.6 -- Evaporative cooler 2 -- No travel beyond Laredo/ Nuevo Laredo area 1.9 -- No. room air conditioners -- 0.3 Distance to neighbor (m) -- 2.4 (95% confidence Mean value for IgM interval) Risk factor seronegative residents or p value No air-conditioning -- (1.3 to 5.2) Evaporative cooler -- (1.2 to 3.3) No travel beyond Laredo/ Nuevo Laredo area -- (1.0 to 3.5) No. room air conditioners 0.6 0.05 Distance to neighbor (m) 3.8 0.003 Table 4. Risk factors associated with anti-dengue IgG seropositivity in Nuevo Laredo/Laredo residents, by univariate analysis Mean value for IgG Factor Prevalence ratio seropositive residents No air-conditioning 1.65 -- No. occupants -- 4.7 Lot size ([m.sup.2]) -- 377 No. room air conditioners -- 0.4 Distance to neighbor (m) -- 3.3 (95% confidence Mean value for IgG interval) Factor seronegative residents or p value No air-conditioning -- (1.27 to 2.15) No. occupants 4.3 0.05 Lot size ([m.sup.2]) 395 0.03 No. room air conditioners 0.7 0.002 Distance to neighbor (m) 3.9 0.03 Table 5. Estimated cost (US dollars) of air-conditioning a house in Texas vs. Taumalipas, Mexico Texas Taumalipas Cost per kilowatt hour (kWh) 0.06119 0.04863 Cost of 25,000 kwh 1,530 1,216 Per capita GDP (a) 34,288 5,014 % of per capita GDP 4.5 24.2 (a) GDP, gross domestic product.
Many persons from the City of Laredo Health Department, the Tamaulipas Secretariat of Health, and the Texas Department of Health contributed to the study. Andrew Spielman gave many helpful comments on the manuscript. Pia Malaney supplied the data for Table 5. The U.S. National Aeronautics and Space Administration National Aeronautics and Space Administration (NASA), civilian agency of the U.S. federal government with the mission of conducting research and developing operational programs in the areas of space exploration, artificial satellites (see satellite, artificial), supplied the figure.
 The investigation plan was reviewed by the Human Subjects Coordinator at the National Center for Infectious Diseases, Centers for Disease Control and Prevention Centers for Disease Control and Prevention (CDC), agency of the U.S. Public Health Service since 1973, with headquarters in Atlanta; it was established in 1946 as the Communicable Disease Center. , and determined to be a public health response that did not require further human subjects review. Blood samples were taken only from consenting adults.
(1.) Rush AB. An account of the bilious bil·ious
1. Of, relating to, or containing bile; biliary.
2. Characterized by an excess secretion of bile.
3. remitting fever as it appeared in Philadelphia in the summer and autumn of the year 1780. Philadelphia: Prichard and Hall; 1789.
(2.) Ehrenkranz NJ, Ventura AK, Cuadrado RR, Pond WL, Porter JE. Pandemic pandemic /pan·dem·ic/ (pan-dem´ik)
1. a widespread epidemic of a disease.
2. widely epidemic.
Epidemic over a wide geographic area.
n. dengue in Caribbean countries and the southern United States-past, present and potential problems. N Engl J Med 1971;285:1460-9.
(3.) Reiter P. Climate change and mosquito-borne disease. Environ Health Perspect 2001;109 (Suppl 1):141-61.
(4.) Turner AG, Magnani RJ, Shuaib M. A not quite as quick but much cleaner alternative to the Expanded Programme on Immunization (EPI EPI
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(5.) Chungue E, Marche G, Plichart R, Boutin JP, Roux Roux , Pierre Paul Émile 1853-1933.
French bacteriologist. His work with the diphtheria bacillus led to the development of antitoxins to neutralize pathogenic toxins. J. Comparison of immunoglobulin G immunoglobulin G
n. Abbr. IgG
The most abundant class of antibodies found in blood serum and lymph and active against bacteria, fungi, viruses, and foreign particles. Immunoglobulin G antibodies trigger action of the complement system. enzyme-linked immunosorbent assay (IgG-ELISA) and haemagglutination Noun 1. haemagglutination - agglutination of red blood cells
agglutination - a clumping of bacteria or red cells when held together by antibodies (agglutinins) inhibition (HI) test for the detection of dengue antibodies: prevalence of dengue IgG-ELISA antibodies in Tahiti. Trans R Soc Trop Med Hyg 1989;83:708-11.
(6.) Innis BL, Nisalak A, Nimmannitya S, Kusalerdchariya S, Chongwasdi V, Suntayakorn S, et al. An enzyme-linked immunosorbent assay to characterize dengue infections where dengue and Japanese encephalitis Japanese Encephalitis Definition
Japanese encephalitis is an infection of the brain caused by a virus. The virus is transmitted to humans by mosquitoes. co-circulate. Am J Trop Med Hyg 1989;40:418-27.
(7.) Pan American Health Organization The Pan American Health Organization (PAHO) is an international public health agency with 100 years of experience in working to improve health and living standards of the countries of the Americas. It serves as the specialized organization for health of the Inter-American System. . Dengue and dengue hemorrhagic fever hemorrhagic fever (hĕm'ərăj`ĭk), any of a group of viral diseases characterized by sudden onset, muscle and joint pain, fever, bleeding, and shock from loss of blood. in the Americas: guidelines for prevention and control. Washington: The Organization; 1994.
(8.) Christophers SR. Aedes aegypti (L.), the yellow fever yellow fever, acute infectious disease endemic in tropical Africa and many areas of South America. Epidemics have extended into subtropical and temperate regions during warm seasons. mosquito: its life history, bionomics bi·o·nom·ics
n. (used with a sing. verb)
[From French bionomique, pertaining to ecology, from bionomie, ecology : Greek bio-, bio- and structure. Cambridge: University Press; 1960.
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(11.) Watson RT, Zinyowera MC, Moss RH, editors. Impacts, adaptations and mitigation of climate change: scientific-technical analyses. Contribution of Working Group II to the Second Assessment of the Intergovernmental Panel on Climate Change “IPCC” redirects here. For other uses, see IPCC (disambiguation).
The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 by two United Nations organizations, the World Meteorological Organization (WMO) and the United Nations Environment (IPCC See IMS Forum. ) Cambridge: Cambridge University Press Cambridge University Press (known colloquially as CUP) is a publisher given a Royal Charter by Henry VIII in 1534, and one of the two privileged presses (the other being Oxford University Press). ; 1996.
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(17.) Molineaux L. The pros and cons pros and cons
the advantages and disadvantages of a situation [Latin pro for + con(tra) against] of modelling malaria transmission. Trans R Soc Trop Med Hyg 1985;79:743-7.
Paul Reiter, Visiting Scholar, Harvard School of Public Health The Harvard School of Public Health is (colloquially, HSPH) is one of the professional graduate schools of Harvard University. Located in Longwood Area of the Boston, Massachusetts neighborhood of Mission Hill, next to Harvard Medical School and Cambridge, Massachusetts, , Building 1, Room 107, 665 Huntington Avenue, Boston, MA 02115 USA; Fax: 617-432-1796; e-mail: email@example.com
Paul Reiter, * Sarah Lathrop, * Michel Bunning, * Brad Biggerstaff, * Daniel Singer, * Tejpratap Tiwari, * Laura Baber, ([dagger]) Manuel Amador, * Jaime Thirion, ([double dagger]) Jack Hayes, ([section]) Calixto Seca, ([paragraph]) Jorge Mendez, ([double dagger]) Bernardo Ramirez, (#) Jerome Robinson, ([dagger]) Julie Rawlings, ([paragraph]) Vance Vorndam, * Stephen Waterman, * Duane Gubler, * Gary Clark, * and Edward Hayes *
* Centers for Disease Control and Prevention, Fort Collins, Colorado The City of Fort Collins, a home rule municipality situated on the Cache la Poudre River along the Colorado Front Range, is the county seat and most populous city in Larimer County, Colorado. , USA; ([dagger]) City of Laredo Health Department, Laredo, Texas, USA; ([double dagger]) Secretaria de Salud, Mexico City, Mexico; ([section]) University of Texas, Boerne, Texas, USA; ([paragraph]) Texas Department of Health, Laredo, Texas, USA; and (#) Secretaria de Salud de Tamaulipas, Nuevo Laredo, Tamaulipas, Mexico
Dr. Reiter is a research entomologist in the Division of Vector-Borne Infectious Diseases, Centers for Disease Control and Prevention (CDC), and current director of a CDC West Nile vires project at the Harvard School of Public Health, Boston, Massachusetts. His interests include the physiology, behavior, and ecology of mosquitoes; the transmission dynamics and epidemiology of the diseases they transmit; and improved methods for their control. In recent years, he has taken a special interest in issues of climate change and vector-borne disease.