Chagas disease is one of the most important endemic diseases in Latin America and it is caused by Trypano- soma cruzi and transmitted by haematophagous insects of the subfamily Triatominae (Hemiptera: Reduviidae). Vector control programmes in the Southern Cone coun-

Chagas disease is one of the most important endemic diseases in Latin America and it is caused by Trypanosoma cruzi and transmitted by haematophagous insects of the subfamily Triatominae (Hemiptera: Reduviidae). Vector control programmes in the Southern Cone countries of South America were highly successful in reducing the impact in about 80% of the original distribution area of Triatoma infestans (Gorla 2002, Schofield et al. 2006), which is the main vector species in the area. The infestation of rural homes was eliminated by systematically spraying the houses with residual insecticides, which interrupted the vectorial transmission of the parasite and decreased the disease incidence. Such programmes were successful in the Southern Cone countries of South America, except in the Gran Chaco region. The Gran Chaco is the second largest ecosystem in Latin America after the Amazon Basin. It covers about one million square kilometres (Pennington et al. 2000) and occupies most of northern Argentina, eastern Bolivia, western Paraguay and a small area of south-western Brazil. The region underwent profound socio-environmental changes starting at the end of the 19th century (Bucher & Schofield 1981), primarily as the result of deforestation for charcoal and fuel wood production and more recently because of the expansion of soybean cultivation (Grau et al. 2005, Zak et al. 2008). The rural communities of the Gran Chaco region are the last places where T. infestans resists the vector control efforts that started in the Chaco region of Argentina in the 1960s. The political and economic instabilities in the region have had a negative effect on effective vector control measures during the last 50 years and the T. infestans populations in the Gran Chaco appear to be the most genetically variable (Panzera et al. 2004, Bargues et al. 2006, Pérez de Rosas et al. 2007, Piccinali et al. 2009) and the best adapted to domestic and peridomestic environments because of their phenotypic plasticity (Catalá et al. 2007, Hernández et al. 2008, Dujardin et al. 2009). Because of their biological characteristics, these populations are the most resilient to vector control interventions (Cécere et al. 2002, Gürtler et al. 2004). The high genetic variability, including a resistance to pyrethroid insecticides (Picollo et al. 2005), seems to be associated with the proximity to the centre of origin of the species, which includes two allopatric genotypes (Panzera et al. 2004, Bargues et al. 2006): the Andean genotype, which probably originated in the Andean valleys of Bolivia, and the non-Andean genotype, whose origin is in the ecotone between the Andean valleys and the Chaco region of Tarija (Bolivia) near the border with Argentina. Historically, Chagas disease has been highly endemic in the Chaco region, most notably in the province of Santiago del Estero in Argentina. During the 1970s and 1980s, around 200 acute cases were reported each year. The vector control interventions in the area decreased the reports of acute cases to about 20 per year after the mid 1990s and to fewer than 10 during the last few years. Northern province of Córdoba, the region south of SantiFinancial support: FONCYT PICTR275, CONICET + Corresponding author: marimore2002@yahoo.com.ar MLM current address: INBIAL, Universidad Nacional de Jujuy, Jujuy, Argentina Received 4 July 2011 Accepted 1 December 2011 Exploring the association between Trypanosoma cruzi infection in rural communities and environmental changes in the southern Gran Chaco