Dengue along the Texas-Mexico Border

Mary Hayden, for NCAR Colloquium, 2006

Dengue is the most frequently reported viral disease transmitted by arthropod vectors, primarily by Aedes aegypti mosquitoes. Dengue (DF) is endemic in most tropical and subtropical areas; over half of the world’s population live in areas at risk for transmission. Globally, there are an estimated 50-100 million cases of dengue infection and 250-500 thousand cases of dengue hemorrhagic fever (DHF) per year. There are four dengue virus serotypes, DEN-1, DEN-2, DEN-3, and DEN-4, all of which can cause DF/DHF. After World War II, the Pan American Health Organization (PAHO) initiated an Ae. aegypti eradication program, primarily designed to control urban yellow fever, which reduced vector populations to below detectable levels in many Central and South American countries, including Mexico. Due to competing health priorities, the program was discontinued, and the species has even wider dispersal than before the eradication campaign (PAHO, 2005). The progressive re-infestation of Latin America with Ae aegyptithat has occurred since the 1970’shas been attributed not only to decreased funding for mosquito control, but also unplanned urbanization in tropical areas and the rise of non-biodegradable products.

In some ways, Mexico typifies the Latin American picture in terms of dengue.

Since the late 1970s, Mexico has progressed from non-endemic to hypoendemic since the introduction of DEN-1, to hyperendemic since the additional circulation of DEN-4 in the early 1980s.

The 2,000 mile U.S.-Mexico border is a “unique region where the geopolitical boundary does not inhibit social and economic interactions nor the transmission of infectious diseases among residents on each side of the border” (Weinberg et al., 2003) Many border cities are immediately adjacent to each other and referred to as ‘sister cities’. As a result of this proximity, there is significant daily human traffic, nearly 3 million pedestrian crossings and over 22 million vehicle crossings between Brownsville and Matamoros in 2004 (US Department of Transportation 2004) across the international border. Brownsville, Texas and Matamoros, Tamaulipas are sister cities across the Rio Grande River (Rio Bravo) in the southernmost region of Texas known as the Lower Rio Grande Valley (LRGV). Located in one of the poorest regions of the United States, Brownsville, Texas has an estimated population of 161,225 and median household income of $24,468 (about 50% of US median income) (US Census Bureau, 2005). Its sister city, Matamoros, has an estimated population of 418,141, (Instituto Nacional de Estadistica Geografia e Informatica, 2005) and a median household income of $10,570. (Gibson et al., 2003). The population is growing rapidly (17% increase from 2000 to 2005), as migrants from Mexico and Central and South America move to the Mexican side of the border to seek employment in the ‘maquiladoras’ (foreign-owned factories); migration to the border has accelerated since the signing of the North American Free Trade Agreement (NAFTA) in 1994.

Brownsville and Matamoros have a semi-tropical climate with an average annual temperature of 74 degrees F and an average annual rainfall of 27.55 inches. (National Climatic Data Center 2005). Housing in the study region is varied. In Brownsville, TX most of the houses are one story constructed of wood, brick, or stucco. Infrastructural services exist on the US side of the border except in unregulated colonias where there is limited piped water, sewage or drainage. On the Mexican side of the border, conditions can be very spare with unpaved roads, no water or waste disposal and little to no drainage. There is a greater variety to the housing structure in Matamoros, particularly in the invasionesr and recently urbanized settlements. Many of the houses in the invasioness are semi-permanent and constructed of a variety of convenient materials including, cardboard, plywood, and corrugated metal siding.

Following the re-establishment of the vector in Mexico, dengue fever has also returned. Dengue outbreaks have occurred annually in Mexico since1978 (Koopman, et al., 1991), and dengue hemorrhagic fever appeared in 1984 (Briseno-Garcia et al. 1996). In 1996, there was an outbreak along the U.S./Mexican border in the Mexican state of Tamaulipas (CDC, 1996). Outbreaks have occurred as recently as 1999 in both Texas and Mexico in the border regions with confirmed cases of dengue on both sides of the border and dengue hemorrhagic fever on the Mexican side (Reiter et al., 2003). The Centers for Disease Control and Prevention (CDC), the State of Texas, and the Secretariat of Health of Mexico have carried out enhanced surveillance through the Border Infectious Disease Surveillance (BIDS) program since 2000.

In 2005, autochthonous transmission of DHF was documented for the first time in the United States in Brownsville, Texas. The presence of the vector, documentation of thousands of cases of dengue in Matamoros, Tamaulipas including almost one thousand cases of clinical DHF suggest that dengue may already be endemic in this border region. Furthermore, the potential exists for dengue to emerge as an important health problem in the United States, especially in rapidly urbanizing US border populations.

The increasing case numbers of dengue and dengue hemorrhagic inLatin Americanecessitate an examination of micro and macro-level changes in human and vector ecology, factors that are critical to understanding the disease transmission dynamics. Simultaneous circulation of multiple strains and large susceptible human populations in rapidly growing urban areas has set the stage for the emergence of dengue and DHF as major public health problems for Mexico and other Latin American countries and raises concern that dengue, a disease that has not been endemic in the continental US in the last half century, is reemerging along US-Mexico Border.

References:

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Pan American Health Organization (PAHO) (2005) Number of Reported Cases of Dengue and Dengue Hemorrhagic Fever, Region of the Americas. Available:

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