Dengue reemergence in 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 Parana 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-[km.sup.2] 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 Maria, Cordoba 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 (Zarate and Campana, 34.2 degrees and 34.4 degrees south, respectively) in February 1996 and October 1996 (early spring) (Aviles G, unpublished data).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.

[Figure 1 ILLUSTRATION OMITTED]

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 22 [degrees] and 26 [degrees], 30 minutes south. A serosurvey was done in Oran, Salvador Mazza, and Guemes (Figure 2). Active surveillance was also conducted in Tartagal. Median temperatures in northern localities (Tartagal and Oran) are 26 [degrees] C in summer and 19 [degrees] C in winter. In Salta city the median temperatures are, 22 [degrees] C in summer and 15 [degrees] C in winter.

[Figure 2 ILLUSTRATION OMITTED]

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

Patient     Travel         Onset of
no.         history        symptoms        MAC-ELISA

1           Brazil         02/14/97        Pos
2           Ecuador        unknown/97      Pos
3           Venezuela      11/16/97        Pos
4           Venezuela      unknown/97      Pos

          Plaque reduction neutralization tests
Patient
no.       D1         D2          D3           D4

1         --          --          --          --
2         1,280       1,280       80         <20
3         --          --          --          --
4         >1,280     >1,280      >1,280       >1,280

-- Not done

Surveillance of Cases in Salta Province

A total of 404 sera were studied from Oran, 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 (Oran, 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.

Table 2. Surveillance for dengue virus infections, Salta Province, Argentina

                positive/                       ELISA
Locality(*)      tested           Onset          IgM

Oran            6/161              --            Pos
                                   --            Neg
                               04/22/97(**)      --
                               04/28/97          --
                               05/16/97          Pos
                               11/16/97          Pos
Salvador        7/113             --             Pos
Mazza                             --             Pos
                                  --             Pos
                                  --             Neg
                                  --             Neg
                                  --             Neg
                                  --             Pos
Tartagal        3/7            08/30/97          Pos
                               10/26/97          Pos
                               11/23/97          Pos
Guemes          1/100             --             Neg
Unknown         2/6               --             Pos
                                                 Pos

                               PRNT
Locality(*)        D1       D2       D3      D4

Oran               20       320      80     <20
                   80        80     160      20
                  <20        80     <20     <20
                   20      >160      20      40
                  640     1,280     640      80
                   --       --       --      --
Salvador          <20        20     <20     <20
Mazza             <20        80      20     <20
                  160      >640    >640      20
                  <20        80      40     <20
                   --        80      80      20
                   20        40      --     <20
                  <20       <20     <20     <20
Tartagal           80      >160    >160     <20
                  <20       160     <20     <20
                > 640     1,280     640      40
Guemes            <20        40     <20     <20
Unknown           <20       <20     <20     <20
                   40     3,160      80     <20

(*) 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.

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 Oran 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 Oran, 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).

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 of immunity 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, Jose 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.

References

(1.) Sabattini MS, Aviles G, Monath TP. Historical, epidemiological and ecological aspects of arboviruses in Argentina: Flaviviridae, Bunyaviridae and Rhabdoviridae. In: An overview of arbovirology in Brazil and neighboring countries. Travassos da Rosa APA, Vasconcelos PFC, Travassos da Rosa JFS, editors. Belem, Brazil: Instituto Evandro Chagas; 1998. p. 113-34.

(2.) Boffi R. Programa de prevencion del dengue y control del Aedes aegypti. In: Temas de zoonosis y enfermedades emergentes. 2do Congreso Argentino de Zoonosis, 1er Congreso Argentino y Latinoamericano de Enfermedades Emergentes y Asociacion Argentina de Zoonosis, editors. 1998;413-419, Buenos Aires.

(3.) Schweigmann N, Boffi R. Aedes aegypti y Aedes albopictus: situacion entomologica en la region. In: Temas de zoonosis y enfermedades emergentes. 2do Congreso Argentino de Zoonosis, 1er Congreso Argentino y Latinoamericano de Enfermedades Emergentes y Asociacion Argentina de Zoonosis (eds.) 1998;259-263, Buenos Aires.

(4.) Aviles G, Cecchini R, Harrington ME, Cichero J, Asis R, Rios C. Aedes aegypti in Cordoba Province, Argentina. J Am Mosq Control Assoc 1997;13:255-8.

(5.) Russel PK, Nisalak A, Sukhavachana P, Vivona S. A plaque reduction test for dengue virus neutralizing antibodies. J Immunol 1967;99:291-6.

(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 co-circulate. Am J Trop Med Hyg 1989;40:418-27.

(7.) Kuno G, Gomez I, Gubler DJ. An ELISA procedure for the diagnosis of dengue infections. J Virol Methods 1991;33:101-13.

(8.) Lanciotti RS, Calisher CH, Gubler DJ, Chang GJ, Vorndam AV. Rapid detection and typing of dengue viruses from clinical samples by using reverse transcriptase-polymerase chain reaction. J Clin Microbiol 1992;30:545-51.

(9.) Gubler DJ, Kuno G, Sather GE, Velez M, Oliver A. 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.

G. Aviles,(*) G. Rangeon,([dagger]) V. Vorndam,([double dagger]) A. Briones,([sections]) P. Baroni,(*) D. Enria,(*) and M.S. Sabattini(*)

(*) Instituto Nacional de Enfermedades Virales Humanas (INEVH) "Dr. J.I. Maiztegui", Administracion Nacional de Laboratorios e Institutos de Salud "Dr. C. Malbran", Pergamino, Argentina; ([dagger]) Ministerio de Salud, Salta, Argentina; ([double dagger]) Centers for Disease Control and Prevention, San Juan, Puerto Rico; and [(sections]) Delegacion Sanitaria Federal, Salta, Argentina

Dr. Aviles 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. Aviles, Instituto Nacional de Enfermedades Virales Humanas "Dr. Julio I. Maiztegui", Monteagudo 2510 (2700) Pergamino, Argentina; fax: [phone]; e-mail: [e-mail].