Emerging Infectious Diseases [Volume 5 No.4 / July - August 1999] Dispatches Dengue Reemergence in Argentina G. Avil‚s,* G. Rangeón,† V. Vorndam,‡ A. Briones,§ P. Baroni,* D. Enria,* and M.S. Sabattini* *Instituto Nacional de Enfermedades Virales Humanas (INEVH) "Dr. J.I. Maiztegui", Administración Nacional de Laboratorios e Institutos de Salud "Dr. C. Malbrán", Pergamino, Argentina; †Ministerio de Salud, Salta, Argentina; ‡Centers for Disease Control and Prevention, San Juan, Puerto Rico; and §Delegación Sanitaria Federal, Salta, Argentina Aedes aegypti, eradicated from Argentina in 1963, has now reinfested the country as far south as Buenos Aires. In 1997, four persons with travel histories to Brazil, Ecuador, or Venezuela had confirmed dengue, and surveillance for indigenous transmission allowed the detection of 19 dengue cases in Salta Province. These cases of dengue are the first in Argentina since 1916 and represent a new southern extension of dengue virus. Dengue History in Argentina Several cases of dengue fever were reported in Argentina at the beginning of this century. Indigenous cases were reported in 1905, 1911, and 1916 in northern Argentina (Chaco, Corrientes, Formosa, and Misiones Provinces) (1). In February and March 1916, an epidemic with 15,000 reported cases occurred in Entre Rios Province along the Uruguay and Paran  Rivers in eastern Argentina. None of these patients had hemorrhagic symptoms. Since this epidemic, no indigenous cases had been reported until 1997 (1). Aedes aegypti In 1955, when the Aedes aegypti eradication campaign began in Argentina, an estimated 1,500,000-km2 area was infested (Figure 1) (1). Santiago del Estero Province had the highest infestation rate, with Ae. aegypti found in 9.4% of localities and 5.3% of houses. This province is characterized by a warm summer and low socioeconomic conditions, with many houses lacking running water (1). The southern extension of Ae. aegypti distribution was 35 degrees south, the latitude of Buenos Aires (1). Buenos Aires was only minimally affected, with only 6 of 199,172 houses infested. By 1963, Ae. aegypti was considered eradicated from the country (1), but in 1986 the National Ministry of Health reported reinfestation in the north (2). The reinfested area is the area that was infested in 1955, including Salta Province. Buenos Aires Province was reinfested in 1991 and the Federal District in 1995 (2,3). In autumn 1997, high infestation levels (35% in 1996 and 18% in 1997) were found in houses in Buenos Aires Province and the Federal District (3). In Villa Mar¡a, C¢rdoba Province (32 degrees south), Ae. aegypti was found in summer (February) of 1995, disappeared in winter, and reappeared in early summer (December 1995) (4). The mosquito was also found in Buenos Aires Province (Z rate and Campana, 34.2 degrees and 34.4 degrees south, respectively) in February 1996 and October 1996 (early spring) (Avilés G, unpublished data). These findings indicate that Ae. aegypti may spend winter in refuges in temperate areas and may not necessarily be reintroduced during summer. The presence of Ae. aegypti in most of the country and the reappearance of dengue fever in neighboring countries (Brazil, Paraguay, and Bolivia) increases the risk for dengue infection in Argentina. The Instituto Nacional de Enfermedades Virales Humanas "Dr. J.I. Maiztegui" is the National Reference Center of Dengue Diagnosis. This article summarizes the first dengue cases diagnosed in Argentina in recent years and documents the southernmost expansion of dengue in South America. The Study DEN 1 HAW, DEN 2 NGC, DEN 3 H87, and DEN 4 H241 strains were obtained from the Centers for Disease Control Laboratory, San Juan, Puerto Rico. Plaque reduction neutralization tests (PRNTs) were performed as described by Russel et al. (5), with an 80% plaque reduction endpoint. The enzyme-linked immunosorbent assay (ELISA) capture IgM test was done as described by Innis et al. (6) and Kuno et al. (7). Polymerase chain reaction (PCR) was done according to the protocol of Lanciotti et al. (8). The isolation attempts and immunofluorescence tests were done by injecting sera into C6/36 cells and using monoclonal antibodies against each of the serotypes (9). Study Area Salta Province is located in northwestern Argentina (Figure 2) in the subtropical area between 22º and 26º, 30 minutes south. A serosurvey was done in Or n, Salvador Mazza, and Guemes (Figure 2). Active surveillance was also conducted in Tartagal. Median temperatures in northern localities (Tartagal and Or n) are 26ºC in summer and 19ºC in winter. In Salta city the median temperatures are 22ºC in summer and 15ºC in winter. Study Participants Blood samples were collected at regional hospitals from patients seeking treatment for any illness. Surveillance of Imported Cases During the epidemiologic surveillance of the cases compatible with dengue, from January to November 1997 our laboratory received 16 samples from returning travelers who had suspected dengue (Table 1). Sera of four patients, returning from Brazil, Ecuador, and Venezuela, were positive by IgM-capture-ELISA. Cases from Ecuador and Venezuela were positive by PRNT, but the serotype could not be determined because of cross-reactions, possibly indicating secondary flavivirus infections. Table 1. Imported dengue cases-Argentina, 1997 ----------------------------------------------------------------- Plaque reduction neutralization tests Patient Travel Onset of no. history symptoms MAC-ELISA D1 D2 D3 D4 ---------------------------------------------------------------- 1 Brazil 02/14/97 Pos --- --- --- --- 2 Ecuador unknown/97 Pos 1,280 1,280 80 <20 3 Venezuela 11/16/97 Pos --- --- --- --- 4 Venezuela unknown/97 Pos >1,280 >1,280 >1,280 >1,280 ---------------------------------------------------------------- ---Not done Surveillance of Cases in Salta Province A total of 404 sera were studied from Or n, Salvador Mazza, Santa Victoria, Tartagal, General Mosconi, Salta city, Junta del San Antonio, Aguaray, and Guemes during April through November 1997. Nineteen serologically positive samples were detected from four of these locations (Orán, Salvador Mazza, Tartagal, and Guemes) (Table 2). Twelve samples were positive by MAC-ELISA, indicating current or recent infections, and three of these had PRNT titers indicating primary DEN 2 infections. Three other samples had cross-reactive antibody patterns indicative of secondary flavivirus infections. Seven other samples were immunoglobulin (Ig)M negative, but positive by PRNT. Three of these showed PRNT titers indicating DEN 2 infections. Six additional samples were positive by PRNT, but the serotype could not be determined. Virus isolation attempts on 36 acute-phase samples had negative results, but one sample was diagnosed as dengue 2 by reverse transcriptase-PCR. Epidemiologic and Clinical Data We obtained epidemiologic and clinical information from nine patients. One, a man from Salvador Mazza, had fever, retroocular pain, malaise, muscle pain, and arthralgias and had traveled to Santa Cruz de la Sierra, Bolivia, before onset of symptoms. Seven other patients reported symptoms including headache, muscle pain, abdominal pain, arthralgias, rash, pharyngitis, and epistaxis. No hemorrhagic manifestations were reported. Six of these patients reported no travel history and must have become infected in Or n or Tartagal. Travel histories were not available from the other two patients. Conclusions Laboratory results show that imported cases of dengue arrived in Argentina during 1997, enabling local transmission in cities like Rosario and Buenos Aires. In northern Argentina, there is continuous traffic with Bolivia, Paraguay, and Brazil, where dengue is known to occur. We report early evidence of DEN 2 virus circulating in northern Argentina, where indigenous cases have occurred in Or n, Tartagal, Guemes, and Salvador Mazza. These cities are generally located along a highway going north into Bolivia, where DEN is endemic. Clinically, all cases were classic dengue fever. High PRNT antibody titers in the acute-phase samples indicated that dengue or other flavivirus infections had probably been present but had gone undetected. Only sporadic cases were found in the area under active surveillance, as in Texas in 1995 when isolated cases of indigenous transmission were detected (10). [fig] Figure 1. Geographic distribution of Aedes aegypti,1955: Dengue risk area in Argentina. [fig] Figure 2. Surveillance for dengue virus infections in Salta Province: Localities with cases. Table 2. Surveillance for dengue virus infections, Salta Province,Argentina ----------------------------------------------------------------- positive/ ELISA PRNT Locality* tested Onset IgM D1 D2 D3 D4 ----------------------------------------------------------------- Orán 6/161 -- Pos 20 320 <20 80 -- Neg 80 160 20 80 04/22/97** -- <20 <20 <20 80 04/28/97 -- 20 >160 40 20 05/16/97 Pos 640 1,280 640 80 11/16/97 Pos -- -- -- -- Salvador 7/113 -- Pos <20 <20 <20 20 Mazza -- Pos <20 <20 80 20 -- Pos 160 >640 >640 20 -- Neg <20 <20 80 40 -- Neg -- 20 80 80 -- Neg 20 -- <20 40 -- Pos <20 <20 <20 <20 Tartagal 3/7 08/30/97 Pos 80 >160 >160 <20 10/26/97 Pos <20 160 <20 <20 11/23/97 Pos 640 >1,280 640 40 Guemes 1/100 -- Neg <20 <20 <20 40 Unknown 2/6 -- Pos <20 <20 <20 <20 Pos 40 >160 <20 80 --------------------------------------------------------------------- *Samples from the following localities were negative by IgM capture-enzyme-linked immunosorbent assay: Santa Victoria (2), General Mosconi (2), Salta city (11), Junta del San Antonio (1) and Aguaray (1). **An acute-phase sample from this case was positive for DEN 2 by RT-PCR. The reestablishment of dengue in Argentina is of concern because of the following risk factors (11): 1) the presence of Ae. aegypti vector in high densities in several places (3); 2) the low levels ofimmunity in the human population in all areas that have been studied (1); 3) endemic virus in neighboring countries (12); and 4) the widespread presence of substandard living conditions, including the lack of running water, in areas where the virus is most likely to be introduced. Air conditioning is uncommon throughout the country, and the climate is subtropical in the north and temperate in the central region, where conditions are suitable for dengue transmission in summer. Surveillance should be continued and expanded in the most susceptible areas to monitor introduction and spread of this reemerging disease. Acknowledgments The authors thank Robert Shope and Elsa Segura for revising this manuscript; Liliana Canini, Nora M. Mellano, Milton Bejarano, Jos‚ A. Rodriguez, Silvia Gonzalez Ayala, and Roque Brun, who attended patients and provided samples; and Cristina C. Bono and Maria Luisa Cacase, who also provided samples. Dr. Avilés is a biologist in charge of the Arbovirus Laboratory, National Reference Center of Dengue Diagnosis, Collaborative Center PAHO/WHO, Instituto Nacional de Enfermedades Virales Humanas "Dr. J.I. Maiztegui"-Administracion Nacional de Laboratorios e Institutos de Salud, Pergamino, Argentina. Her areas of expertise are arbovirology and medical entomology (mosquitoes). Her research interests include arboviruses (in humans and vertebrates), DEN, YF, WEE, EEE, VEE, and the competence of mosquitoes as vectors for arboviruses. Address for correspondence: G. Avilés, Instituto Nacional de Enfermedades Virales Humanas "Dr. Julio I. Maiztegui", Monteagudo 2510 (2700) Pergamino, Argentina; fax: 54-24-774-33045; e-mail: Gaby@inevh.sld.ar. References 1. Sabattini MS, Avilés G, Monath TP. 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Mosquito cell cultures and specific monoclonal antibodies in surveillance for dengue viruses. Am J Trop Med Hyg 1984;33:158-65. 10. Centers for Disease Control and Prevention. Dengue fever at the U.S. Mexico border, 1995-1996. MMWR Morb Mortal Wkly Rep 1996;45:841-4. 11. Gubler DJ. Dengue. In: The arboviruses: epidemiology and ecology. Monath TP, editor. II. Boca Raton, FL: CRC Press; 1988. p. 223-60. 12. Pan American Health Organization. Dengue and dengue hemorrhagic fever in the Americas: guidelines for prevention and control. Washington, D.C. 1994; Scientific publication No. 548. Emerging Infectious Diseases National Center for Infectious Diseases Centers for Disease Control and Prevention Atlanta, GA URL: ftp://ftp.cdc.gov/pub/EID/vol5no4/ascii/.txt Please note that figures and equations are not available in ASCII format; their placement within the text is noted by [fig] and [eq], respectively. Greek symbols are spelled out. 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