| Vol. 98(6) September 2003 |
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Prevalence of Infection with Hantavirus in Rodent Populations of Central Argentina Vol. 98(6): 727-732, September 2003
Olga V Suárez/+, Gerardo R Cueto, Regino Cavia, Isabel E Gómez Villafañe/*, David N Bilenca/*, Alexis Edelstein**, Paula Martínez**, Sergio Miguel**, Carla Bellomo**, Karina Hodara, Paula J Padula*/**, María Busch/*
Laboratorio de Ecología de Poblaciones, Departamento de Ecología, Genética y Evolución, Universidad de Buenos Aires, Facultad de Ciencias Exactas y Naturales, Ciudad Universitaria, Pabellón II, 4º piso, (C1428EHA), Buenos Aires, Argentina *Consejo Nacional de Investigaciones Científicas y Tecnológicas Buenos Aires, Argentina **Instituto Nacional de Enfermedades Infecciosas, Anlis, Malbrán, Argentina
We studied hantavirus seroprevalence and virus variability in rodent populations in Diego Gaynor, northwest of Buenos Aires province, Argentina. Rodent samplings were conducted in railroads and cropfield borders in March and July 1999, September and December 2000, and March 2001. Antibody detection was performed by an enzyme link immunosorbent assay (ELISA), using the recombinant nucleoprotein of Andes (AND) virus as antigen. Tissue samples were taken from positive antibody individuals in order to confirm the presence of hantavirus genomic material and to identify virus genotypes. Akodon azarae was the most abundant species, followed by Oligoryzomys flavescens, while Calomys laucha and C. musculinus were rarely caught. We found a rate of seroprevalence of 9.3% for a total sample of 291 A. azarae and 13.5% for 37 O. flavescens. After molecular analyses of hantavirus, we confirmed the presence of hantavirus genomic material in 16 individuals with ELISA (+) results and two individuals with ELISA (-). Four amplimers for each species were sequenced and compared to the corresponding sequences of representative hantaviruses. We identified the AND Cent Lec from three O. flavescens, and the Pergamino virus from four A. azarae and from one O. flavescens. A. azarae males had higher seroprevalence than females, and heavier individuals showed higher seroprevalence than lighter ones. We did not find seroprevalence differences according to sex in O. flavescens, although this result may have been produced by the low sample size. The lowest seroprevalence was found in a period of high rodent density, when juveniles prevailed in the population. We found higher seroprevalences than those detected in previous studies for other localities of central Argentina where cases of hantavirus pulmonary syndrome (HPS) have been reported. The presence of AND Cent Lec virus in rodent populations of the study area, which is responsible of HPS cases in central Argentina, suggests that human populations are at risk of HPS disease, although there were not reported cases of this disease until today.
Key words: sigmodontine rodents - hantavirus pulmonary syndrome - seroprevalence - Argentina
Hantavirus pulmonary syndrome (HPS) is a severe and often fatal cardiopulmonary disease that affects many people in America. After the outbreak of HPS in 1993 in Southwestern United States (Nichol et al. 1993), there was an increase in reports from cases in South America. Between 1993-2001, there have been 310 confirmed cases of HPS in Argentina, 91 in Paraguay, 204 in Chile, 167 in Brazil, 27 in Uruguay and 11 in Bolivia (PAHO 2002). Rodent species of the subfamily Sigmodontinae are the main reservoirs of different types of hantaviruses throughout the continent. Calomys laucha was identified as the reservoir of the virus Laguna Negra, the etiologic agent of HPS in Paraguay (Yahnke et al. 2001), while three species of Oligoryzomys have been related to hantavirus transmission: O. longicaudatus (in Chile and Southern Argentina), O. chacoensis (in Northern Argentina, Padula et al. 2002), and O. flavescens in Central Argentina and Uruguay (Levis et al. 1998, González della Valle et al. 2002). Serosurveys of wild rodents conducted in areas of Brazil where cases of HPS occurred found that Bolomys lasiurus and Oligoryzomys spp. may be potential reservoirs of hantaviruses in this country (Romano-Lieber et al. 2001). On the other hand, another study conducted in Brazil found a a seroprevalence of 28.8% in Holochilus sciureus (Vasconcelos et al. 2001). In Argentina, the first cases of HPS were recorded and characterized in 1995 in the Southwest (López et al. 1996). Nowadays, the occurrence of cases is concentrated in three geographically isolated areas: North (Salta and Jujuy provinces), Center (Buenos Aires, Santa Fe and Entre Ríos provinces), and Southwest (Neuquén and Río Negro provinces). In an extensive study conducted in sites were HPS cases occurred, many sigmodontine species were found infected with hantavirus, with seroprevalences which varied between 1.5 and 10.2%, depending on the area and species (Calderón et al. 1999, Cantoni et al. 2001, Sosa Estani et al. 2002, Gonzalez della Valle et al. 2002). López et al. (1996, 1997) described the virus associated to HPS cases in Argentina, Andes virus (AND), as a new type of hantavirus. This virus circulates in Argentina, Chile and Uruguay with different lineages that are characteristics of the different areas (Padula et al. 2000a). Although three species of the genus Oligoryzomys were identified as associated to hantavirus that caused HPS in Argentina, the reservoirs of two lineages of virus which caused HPS in Buenos Aires (AND Cent Buenos Aires and AND Cent Plata; Martínez et al. 2001) have not been identified yet. Moreover, there are two other types of virus, which have not been associated to human disease, until now, were identified from other sigmodontine species inhabiting the Buenos Aires province: Maciel virus (in Necromys obscurus), and Pergamino (in Akodon azarae) (Levis et al. 1998). Previous studies of rodent hantavirus reservoirs in US (Abbott et al. 1999, Mills et al. 1999) and Argentina (Cantoni et al. 2001) suggest that the prevalence of infection is higher for adult males than for females and juveniles. Differences among demographic groups have been related to behavioral factors as agonistic interactions, to home range size, and to the age effect that increase the probability of being infected, suggesting that horizontal transmission is the main mechanism of maintaining the virus in nature (Abbott et al. 1999, Mills et al. 1999). Although seroprevalence variations according to changes in population density and structure have been described (Graham & Chomel 1997, Kuenzi et al. 1999, Mills et al. 1999, Biggs et al. 2000, Cantoni et al. 2001), there is still not a clear pattern of variation of seroprevalence with density. When higher density is accompanied with an increase in the proportion of juveniles in the population, a lower seroprevalence have been related to a dilution effect (Mills et al. 1999). This work shows results of a study conducted in order to study the prevalence of infection with different types of hantavirus in rodent populations of northwest Buenos Aires province, Argentina, and its variation according to species and demographic sub classes.
Sources of financial support: Universidad de Buenos Aires (grant UBACYT TX 58), Consejo Nacional de Investigaciones Cientificas y Tecnológicas, Argentina (grant PIP 548/98), and Fundación "Alberto J. Roemmers" (Argentina) +Corresponding author. Fax: +54-11-4576.3384. E-mail: osuarez@bg.fcen.uba.ar Received 4 December 2002 Accepted 10 July 2003 |
