Insights sobre a evolução e dispersão da resistência aos piretróides entre Triatoma infestans andinos silvestres da Bolívia

Abstract: Sylvatic populations of Triatoma infestans represent a challenge to Chagas disease control as they are not targeted by vector control activities and may play a key role in post-spraying house reinfestation. Understanding sylvatic foci distribution and gene flow between sylvatic and domestic populations is crucial to optimize vector control interventions and elucidate the development and spread of insecticide resistance. Herein, the genetic profiles of five Andean T. infestans populations from Bolivia with distinct insecticide susceptibility profiles were compared. Multilocus genotypes based on eight microsatellites and the DNA sequence of a fragment of the cytochrome B (cytB) gene were obtained for 92 individuals. CytB haplotypes were analyzed with previously reported Bolivian T. infestans haplotypes to evaluate putative historical gene flow among populations. Each specimen was also screened for two nucleotide mutations in the sodium channel gene (kdr), related to pyrethroid resistance (L1014 and L9251). Significant genetic differentiation was observed among all populations, although individuals of admixed origin were detected in four of them. Notably, the genetic profiles of adjacent domestic and sylvatic populations of Mataral, characterized by higher levels of insecticide resistance, support their common ancestry. Only one sylvatic individual from Mataral carried the kdr mutation L1014, suggesting that this mechanism is unlikely to cause the altered insecticide susceptibility observed in these populations. However, as the resistance mutation is present in the area, it has the potential to be selected under insecticidal pressure. Genetic comparisons of these populations suggest that insecticide resistance is likely conferred by ancient trait(s) in T. infestans sylvatic populations, which are capable of invading domiciles. These results emphasize the need for stronger entomological surveillance in the region, including early detection of house invasion, particularly post-spraying, monitoring for resistance to pyrethroids and the design of integrative control actions that consider sylvatic foci around domestic settings and their dispersion dynamics.

Pyrethroid Resistance Associated With a Decreased DEET Repellency in the Common Bed Bug (Hemiptera: Cimicidae)

The global resurgence of the bed bug (Cimex lectularius L.) and the widespread resistance of this insect to pyrethroid insecticides have created the need to find alternatives to chemical control. Thus, synthetic or natural repellents have been considered as a suitable choice to control bed bug infestations. Repellents not only keep insects away from their hosts, but also allow a decrease in insecticide selection pressure. The aim of this study was to evaluate the repellence effectivity of DEET against two bed bug colonies from Argentina (a susceptible one and a fieldcollected pyrethroid-resistant one), under two starving periods. We found different repellent effects of DEET on the two C. lectularius colonies and no differences between the two starving periods. In fact, DEET had a lower effect on the insecticide-resistant colony. The methodology used in this study proved to be useful to test the variation of the effect of DEET between pyrethroid-susceptible and -resistant bed bugs.

Beating the odds: Sustained Chagas disease vector control in remote indigenous communities of the Argentine Chaco over a seven-year period / Superando as probabilidades: controle sustentado do vetor da doença de Chagas em comunidades indígenas remotas do Chaco argentino durante um período de sete anos

Background: Rapid reinfestation of insecticide-treated dwellings hamper the sustained elimination of Triatoma infestans, the main vector of Chagas disease in the Gran Chaco region. We conducted a seven-year longitudinal study including community-wide spraying with pyrethroid insecticides combined with periodic vector surveillance to investigate the house reinfestation process in connection with baseline pyrethroid resistance, housing quality and household mobility in a rural section of Pampa del Indio mainly inhabited by deprived indigenous people (Qom). Methodology/principal findings: Despite evidence of moderate pyrethroid resistance in local T. infestans populations, house infestation dropped from 31.9% at baseline to 0.7% at 10 months post-spraying (MPS), with no triatomine found at 59 and 78 MPS. Household-based surveillance corroborated the rare occurrence of T. infestans and the house invasion of other four triatomine species. The annual rates of loss of initially occupied houses and of household mobility were high (4.6-8.0%). Housing improvements did not translate into a significant reduction of mud-walled houses and refuges for triatomines because most households kept the former dwelling or built new ones with mud walls. Conclusions/significance: Our results refute the assumption that vector control actions performed in marginalized communities of the Gran Chaco are doomed to fail. The larger-than-expected impacts of the intervention program were likely associated with the combined effects of high-coverage, professional insecticide spraying followed by systematic vector surveillance-and-response, broad geographic coverage creating a buffer zone, frequent housing replacement and residential mobility. The dynamical interactions among housing quality, mobility and insecticide-based control largely affect the chances of vector elimination.

Toxicological, Enzymatic, and Molecular Assessment of the Insecticide Susceptibility Profile of Triatoma infestans (Hemiptera: Reduviidae, Triatominae) Populations From Rural Communities of Santa Cruz, Bolivia

A wide range of insecticide resistance profiles has been reported across Bolivian domestic and sylvatic populations of Triatoma infestans (Klug, 1834) (Hemiptera, Reduviidae), including some with levels proven to be a threat for vector control. In this work, the insecticide profile of domestic T. infestans was studied with standardized toxicological bioassays, in an area that has not undergone consistent vector control. F1 first-instar nymphs hatched in laboratory from bugs captured in three communities from the Santa Cruz Department were evaluated with different insecticides. Moreover, the enzymatic activity of esterases and cytochrome P450 monooxygenases was measured in individual insects to evaluate the possible mechanism of metabolic resistance to pyrethroids. In addition, the DNA sequence of sodium channel gene (kdr) was screened for two point mutations associated with pyrethroid resistance previously reported in T. infestans. All populations showed reduced susceptibility to deltamethrin and α-cypermethrin, albeit the RR50 values varied significantly among them. Increased P450 monooxygenases and permethrate esterases suggest the contribution, as detoxifying mechanisms, to the observed resistance to deltamethrin in all studied populations. No individuals presented either mutation associated to resistance in the kdr gene. The level of susceptibility to α-cypermethrin, the insecticide used by the local vector control program, falls within an acceptable range to continue its use in these populations. However, the observed RR50 values evidence the possibility of selection for resistance to pyrethroids, especially to deltamethrin. Consequently, the use of pyrethroid insecticides should be closely monitored in these communities, which should be kept under entomological surveillance and sustained interventions.

Resistencia a insecticidas en Blattella Germánica de Buenos Aires / Resistance to insecticides in Blatella germanica from Buenos Aires

Se determinó la línea base de susceptibilidad a delta deltametrina, cipermetrina, cxlorpirifós y fenitrotión en ninfas del primer estadio de la cucaracha alemana, Blatella germanica, provenintes de una población susceptible a insecticidas mantenida en laboratorio (cepa CIPEIN). En base a los valores de DL50, se observó el siguiente orden decrteciente de toxicidad: deltametrina > clorpirifós > cipewrmetrina fenitrotión. La DL99 de cada uno de estos insecticiodas fue aplicada a la descendencia de individuos recolectados en cuatro sitios de Buenos Aires y a individuos de una cepa resistente a deltametrina criada en laboratorio desde 1994. En todos los casos, al menos un insecticida produjop menor mortalidad que la observada en la cepa susceptible, sigiriendo la excistencia de resistencia. Se obtuvieron valores de DL50 y los Grados de Resistencia (GR) a deltametrina para cada muestra. En todos los casos se observó resistencia a este insecticida, con GR que variaron entre 7,3 y 75,4.