Dengue Fever at the U.S.-Mexico Border, 1995-1996

Dengue is a mosquito-transmitted acute disease caused by any of four virus serotypes (DEN-1, DEN-2, DEN-3, and DEN-4) and is characterized by acute manifestations that can include fever, headache, myalgia, arthralgia, rash, nausea, and vomiting (1). On August 25, 1995, public health authorities in Mexico notified the Texas Department of Health (TDH) of an ongoing outbreak of dengue fever in the state of Tamaulipas, which borders south Texas (Figure_1). Because of the year-round presence of the Aedes aegypti mosquito (a major vector for dengue) in southernmost Texas and the frequent movement of persons across the U.S.-Mexico border, the outbreak in adjacent Tamaulipas suggested an increased potential for imported and autochthonous cases in Texas, as had occurred during 1980 and 1986 (2). In response to the notification from Mexico, TDH intensified surveillance efforts for dengue, resulting in identification of 29 laboratory-diagnosed cases in Texas residents, including seven persons with no history of travel outside the state. This report summarizes results of dengue surveillance in the U.S.-Mexico border area during 1995-1996. Mexico

During July-December 1995, health authorities in Tamaulipas (1994 population: 2,459,087) reported 4758 suspected cases of dengue to health authorities in Mexico. Dengue hemorrhagic fever (DHF) * was reported in 37 (1%) of these cases. The largest numbers of cases were reported from the cities of Reynosa (2706 cases), adjacent to McAllen (Hidalgo County), Texas; Tampico (1404 cases), approximately 250 miles south of the border; and Matamoros (408 cases), adjacent to Brownsville (Cameron County), Texas. Dengue infection was laboratory-diagnosed by positive immunoglobulin M (IgM)-capture enzyme-linked immunosorbent assay (ELISA) (578 cases) and viral isolation (64 cases). Viral isolates included DEN-1 from southern Tamaulipas, DEN-3 and DEN-4 from northern Tamaulipas, and DEN-2 from both areas.

In Reynosa, epidemic activity began in July and peaked in October. DEN-2, DEN-3, and DEN-4 viruses were isolated from cases in Reynosa. Although cases occurred in all age groups, most (70%) were in persons aged 15-44 years; 56% of cases occurred in females. Hemorrhagic manifestations were noted in 218 patients (8%), but only 28 (1%) patients developed DHF. Mosquitoes were collected in Reynosa from mid-October through mid-November and included 847 Ae. aegypti, 1033 Ae. albopictus, and 420 Aedes spp. DEN-2 was recovered from two pools of Ae. aegypti mosquitoes.

After recognition of the outbreak, health authorities initiated community education and mosquito-control activities in Reynosa. High school students distributed educational pamphlets, and vector-control personnel conducted clean-up campaigns and treatment of larval habitats with Abate(Registered) ** (temephos) in all sections of the city. Ultra-low volume (ULV) applications of malathion were conducted in 179 neighborhoods.

In Tamaulipas, transmission of dengue ended by late December 1995. However, during the first week of July 1996, cases of dengue-like illness were reported in Tampico. Of 28 acute- or convalescent-phase serum samples obtained during August and sent to CDC for testing, 17 were positive for IgM dengue antibodies, and cultures of five samples yielded DEN-1. Texas

Because of the reported outbreak in Tamaulipas, on August 25, 1995, TDH issued a dengue alert memorandum by facsimile to all local health departments, infection-control practitioners, and infectious disease physicians in south Texas. Packets of information about dengue prevention were mailed to 13,000 primary-care and emergency department physicians throughout the state. Community education efforts included a press release advising the public about the threat of dengue and recommendations for preventing mosquito exposure, the distribution of informational material on dengue prevention and the mosquito life cycle (6000 posters and 200,000 pamphlets in English and Spanish). TDH conducted active surveillance for dengue-like illness through telephone calls and personal visits to area hospitals and clinical and reference laboratories. Studies of vector densities in selected habitats confirmed that both Ae. albopictus and Ae. aegypti were abundant in this area (4).

Specimens from 273 Texas residents with suspected cases were tested at CDC; of these, 23 had virologic or serologic evidence of dengue infection. TDH received reports from commercial laboratories of seven additional patients with positive serologic tests. Of the 29 patients with laboratory-diagnosed dengue, eight reported recent travel to areas with endemic dengue outside Mexico. Of the remaining 21 persons, 14 reported recent travel to Mexico, and seven reported no travel outside Texas. The seven persons with domestically acquired dengue were women aged 20-90 years (median: 40 years). Dates of onset of illness among these seven cases were from mid-September through mid-November 1995. Four of these patients resided in Hidalgo County and three in Cameron County. DEN-2 was isolated from one of the four Hidalgo County residents, and DEN-4 was isolated from one of the three Cameron County residents. TDH and CDC are investigating an additional case of suspected dengue in a person with no travel history.

Health authorities in Mexico periodically update TDH about dengue activity in Mexico. In addition, TDH is continuing its surveillance efforts.

Reported by: J Rawlings, MPH, C Burgess, L Tabony, MPH, R Campman, PhD, K Hendricks, MD, G Stevenson, MD, L Vela, MD, D Simpson, MD, State Epidemiologist, Texas Dept of Health. R Tapia-Conyer, MD, C Ruiz Matus, MD, H Gomez-Dantes, MD, R Montesanos, MD, A Flisser, MD, B Briseno, S Ibanez Bernal, General Direction of Epidemiology, and National Institute for Epidemiological Diagnosis and Reference, Mexico City. C Castro Medina, MD, G Flores, MD, G Diaz Coello, MD, Coordinated Health Svcs, Tamaulipas, Mexico. J Hayes, PhD, Univ of Texas Health Sciences Center, San Antonio. GB Craig Jr, PhD, MS Blackmore, PhD, JP Mutebi, PhD, Univ of Notre Dame, South Bend, Indiana. Dengue Br, Div of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: Since 1994, epidemics of dengue have increased substantially in the Caribbean, Mexico, and South and Central America and have been associated with circulation of all four dengue virus serotypes. In 1995, approximately 240,000 cases of dengue were reported in Central and South America (Pan American Health Organization, unpublished data, 1995). In Mexico, laboratory and morbidity surveillance have been strengthened for monitoring disease trends. During 1984-1993, only 26 cases of DHF were reported in Mexico; in comparison, during 1994 and 1995, DHF occurred in 30 and 92 patients, respectively, with laboratory-confirmed dengue. During 1995, most cases of dengue in Tamaulipas were attributed to DEN-2; however, DEN-3 was isolated for the first time in Mexico, occurring in areas from southern Mexico to Tamaulipas (5). Because of the increased risk for epidemic DHF in Mexico, the Ministry of Health has initiated an intensive prevention and control program in areas with endemic dengue. The program emphasizes laboratory-supported dengue surveillance, health education, community participation, and intensive mosquito control.

Although dengue fever is not endemic in the United States, imported cases are diagnosed each year and additional cases probably are undetected. The seven cases acquired locally in Texas during 1995 underscore that, during periods of intense dengue activity in contiguous Mexico, indigenous dengue can occur in adjacent areas of south Texas. During 1980, following a 2-year period of intense transmission of dengue in Mexico, cases occurred among residents of Texas; these cases were the first to be indigenously transmitted in the United States since 1945. During 1986, nine of the 17 laboratory-diagnosed infections in Texas were acquired locally (2).

Although Ae. aegypti is the principal epidemic dengue vector worldwide, Ae. albopictus has been associated with disease transmission, primarily as a maintenance vector in Asia (6). Both species are present in south Texas and northeastern Mexico and in areas of Brazil, the Dominican Republic, and Guatemala; however, Ae. albopictus has not been documented to be a vector for dengue in the Americas. In Texas, the primary larval habitat for Ae. aegypti is water containers (e.g., flower pots, bird baths, and old cans or tires). These containers also are an important larval habitat in Mexico and, in addition to other habitats (e.g., tree holes) may be inhabited by Ae. albopictus larvae. Aedes larval habitats can be eliminated by removing, emptying, or covering these containers.

Cases of suspected dengue should be reported to state and territorial health departments. Reports should include a clinical summary, dates of onset of illness and blood collection, and other relevant epidemiologic information (e.g., a detailed travel history with dates and location of travel). Serum samples should be sent for confirmation through state health department laboratories to CDC's Dengue Branch, Division of Vector-Borne Infectious Diseases, National Center for Infectious Diseases, 2 Calle Casia, San Juan, PR 00921-3200; telephone (787) 766-5181; fax (787) 766-6596.

References

1. Pan American Health Organization. Dengue and dengue hemorrhagic fever: guidelines for prevention and control. Washington, DC: Pan American Health Organization, 1994:12-3.

2. Rigau-Perez JG, Gubler DJ, Vorndam AV, Clark GG. Dengue surveillance -- United States, 1986-1992. In: CDC surveillance summaries (July). MMWR 1994;43(no. SS-2):7-19.

3. Tassniyom S, Vasanawathana S, Chirawatkul A, Rojanasuphot S. Failure of high-dose methylprednisolone in established dengue shock syndrome: a placebo-controlled, double-blind study. Pediatrics 1993;92:111-5.

4. Barnett B, Hayes J. Dengue mosquito vectors in Texas. Disease Prevention News 1995;55:2-3.

5. Briseno-Garcia B, Gomez-Dantes H, Argott-Ramirez E, et al. Potential risk for dengue hemorrhagic fever: the isolation of serotype dengue-3 in Mexico. Emerging Infectious Diseases 1996;2:133-5.

6. Gubler DJ. Dengue. In: Monath TP, ed. The arboviruses: epidemiology and ecology. Boca Raton, Florida: CRS Press, 1988;2:223-60.

* DHF is defined as fever, platelet count less than or equal to 100,000/mm3, any hemorrhagic manifestation, and excessive capillary permeability (demonstrated by hemoconcentration, pleural or abdominal effusions, or hypoproteinemia) (1) and may be associated with death rates up to 12% even when treated (3). 

** Use of trade names and commercial sources is for identification only and does not imply endorsement by the Public Health Service or the U.S. Department of Health and Human Services.

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