Susceptibility to deltamethrin of wild and domestic populations of Triatoma infestans of the Gran Chaco and the Inter-Andean Valleys of Bolivia

Abstract

BackgroundThe persistence of Triatoma infestans and the continuous transmission of Trypanosoma cruzi in the Inter-Andean Valleys and in the Gran Chaco of Bolivia are of great significance. Coincidentally, it is in these regions the reach of the vector control strategies is limited, and reports of T. infestans resistance to insecticides, including in wild populations, have been issued. This study aims to characterize the susceptibility to deltamethrin of wild and domestic populations of T. infestans from Bolivia, in order to better understand the extent of this relevant problem.MethodsSusceptibility to deltamethrin was assessed in nine, wild and domestic, populations of T. infestans from the Gran Chaco and the Inter-Andean Valleys of Bolivia. Serial dilutions of deltamethrin in acetone (0.2 μL) were topically applied in first instar nymphs (F1, five days old, fasting, weight 1.2 ± 0.2 mg). Dose response results were analyzed with PROBIT version 2, determining the lethal doses, slope and resistance ratios (RR). Qualitative tests were also performed.ResultsThree wild T. infestans dark morph samples of Chaco from the Santa Cruz Department were susceptible to deltamethrin with RR50 of <2, and 100% mortality to the diagnostic dose (DD); however, two domestic populations from the same region were less susceptible than the susceptibility reference lineage (RR50 of 4.21 and 5.04 respectively and 93% DD). The domestic population of Villa Montes from the Chaco of the Tarija Department presented high levels of resistance (RR50 of 129.12 and 0% DD). Moreover, the domestic populations from the Valleys of the Cochabamba Department presented resistance (RR50 of 8.49 and 62% DD), the wild populations were less susceptible than SRL and T. infestans dark morph populations (RR50 < 5).ConclusionThe elimination of T. infestans with pyrethroid insecticides in Brazil, Uruguay, Chile, and its drastic reduction in large parts of Paraguay and Argentina, clearly indicates that pyrethroid resistance was very uncommon in non-Andean regions. The pyrethroid susceptibility of non-Andean T. infestans dark morph population, and the resistance towards it, of Andean T. infestans wild and domestic populations, indicates that the Andean populations from Bolivia are less susceptible.

A methodology based on insecticide impregnated filter paper for monitoring resistance to deltamethrin in Triatoma infestans field populations

“…Different variants of the methodology of papers impregnated with insecticides were applied for studies of insecticide resistance in triatomines. Early studies during the 1970s followed the first instructions of WHO by which fifth instar nymphs collected in the field were exposed to strips of papers impregnated with insecticides located inside test tubes with different exposure times and mortality registration time depending on the authors, species and insecticides (WHO, 1963;Fox & Bayona, 1966;Gonzalez-Valdivieso et al, 1971;Cockburn, 1972;Nocerino, 1975;Nelson, 1994). After the introduction of pyrethroid insecticides, and due to the lack of standardization in exposure time, mortality registration time, impregnation of papers and individuals evaluated, the WHO described a new protocol of insecticide impregnated filter papers for T. infestans (WHO, 1994) and R. prolixus (WHO, 2001).…”

“…As no effective treatment is available for the chronic forms of the disease, vector chemical control represents the best way to reduce the incidence of disease (Zerba, 1999). After application of pyrethroids insecticides in dwellings and peri-domiciliary areas, intergovernmental control programmes reduced the geographic range and infestation prevalence of major triatomine vectors leading to the interruption of transmission mediated by Triatoma of deficient control Toloza et al, 2008;Germano et al, 2010Germano et al, , 2012Germano et al, , 2013Lardeux et al, 2010;Gomez et al, 2014).…”

Improved vector control of Triatoma infestans limited by emerging pyrethroid resistance across an urban-to-rural gradient in the Argentine Chaco

“…Ecological, socio-demographic, political and economic constraints hinder vector control success in the Gran Chaco, including the lower effectiveness of pyrethroid insecticides in peridomestic structures, limited coverage of control actions, disperse rural settlements with limited access, operational and resource limitations, occurrence of sylvatic foci, among others [ 12 , 13 ]. This epidemiological scenario gained more complexity over the 1990s with the emergence of pyrethroid resistance in T. infestans and associated control failures across northern Argentina and Bolivia [ 14 – 18 ]. The issue of rapid recovery of triatomine populations following insecticide spraying campaigns cuts across the major triatomine vector species, such as Triatoma dimidiata , Triatoma brasiliensis , Rhodnius ecuadoriensis and Rhodnius prolixus (e.g., [ 19 – 23 ]).…”

Detoxificación de insecticidas en triatominos: un enfoque transcriptómico

“…Los resultados sugirieron que existen dos focos de resistencia diferenciados, uno asociado a la mutación L1014F en la frontera Argentino-Boliviana y el otro asociado a la mutación L925I en la zona del Chaco argentino (Sierra et al 2016) . Estos resultados concuerdan con el hallazgo de poblaciones resistentes a lo largo de esa distribución geográfica (Picollo et al 2005;Santo Orihuela et al 2008;Toloza et al 2008;Germano et al 2010Germano et al , 2012Germano et al , 2013Germano et al , 2014Lardeux et al 2010;Depickère et al 2012;Roca-Acevedo et al 2013;Gomez et al 2014).…”

“…El estudio de las causas de la resistencia tiene implicancias para el desarrollo de herramientas de control más eficientes, dado que el uso racional de insecticidas requiere un conocimiento extensivo sobre sus propiedades toxicológicas, la biología de los insectos y la interacción insecto-insecticida (Alzogaray & Zerba 2017) . En consecuencia, en los últimos años diversos estudios han aportado conocimiento sobre el fenómeno de resistencia a piretroides en triatominos, permitiendo detectar poblaciones resistentes y analizar su distribución geográfica (Picollo et al 2005;Santo Orihuela et al 2008;Toloza et al 2008;Lardeux et al 2010;Germano et al 2010Germano et al , 2012Germano et al , 2013Depickère et al 2012;Roca-Acevedo et al 2013;Gomez et al 2014;Sierra et al 2016;Fronza et al 2016). En cuanto a los mecanismos subyacentes, se han descripto mutaciones kdr (Fabro et al 2012;Capriotti et al 2014;Sierra et al 2016) y cambios en la cutícula de los insectos (Pedrini et al 2009;Calderón-Fernández et al 2017;Dulbecco et al 2018) asociadas a resistencia.…”