Unexpected Failures to Control Chagas Disease Vectors With Pyrethroid Spraying in Northern Argentina

Abstract

Effectiveness of the elimination efforts against Triatoma infestans (Klug) in South America through residual application of pyrethroid insecticides has been highly variable in the Gran Chaco region. We investigated apparent vector control failures after a standard community-wide spraying with deltamethrin SC in a rural area of northeastern Argentina encompassing 353 houses. Insecticide spraying reduced house infestation less than expected: from 49.5% at baseline to 12.3 and 6.7% at 4 and 8 mo postspraying, respectively. Persistent infestations were detected in 28.4% of houses, and numerous colonies with late-stage bugs were recorded after the interventions. Laboratory bioassays showed reduced susceptibility to pyrethroids in the local bug populations. Eleven of 14 bug populations showed reduced mortality in diagnostic dose assays (range, 35 ± 5% to 97 ± 8%) whereas the remainder had 100% mortality. A fully enclosed residual bug population in a large chicken coop survived four pyrethroid sprays, including two double-dose applications, and was finally suppressed with malathion. The estimated resistance ratio of this bug population was 7.17 (range, 4.47–11.50). Our field data combined with laboratory bioassays and a residual foci experiment demonstrate that the initial failure to suppress T. infestans was mainly because of the unexpected occurrence of reduced susceptibility to deltamethrin in an area last treated with pyrethroid insecticides 12 yr earlier. Our results underline the need for close monitoring of the impact of insecticide spraying to provide early warning of possible problems due to enhanced resistance or tolerance and determine appropriate responses.

Identifying Current and Missing Knowledge in the Control of Pyrethroid-Resistant Triatoma infestans, Vector of Chagas Disease

“…Similarly to what was observed in S. Mazza, T. infestans populations of a neighboring area (Pampa del Indio, Chaco) located 40 km from La Esperanza, presented significantly lower levels of resistance to deltamethrin despite their geographical proximity (Gurevitz et al, 2012).…”

The impact of landscape transformation on the reinfestation rates of Rhodnius prolixus in the Orinoco Region, Colombia

“…before and after fumigation was similar for all revisiting times. This finding is controversial, because the expected effectiveness of the insecticide is supposed to last a few months and decay with time (Gurevitz et al, 2012;Gürtler et al, 2004). We see a homogenous average drop in the I.I.…”

“…These methods showed success in some regions but seem to be of limited effectiveness where insect populations live in sylvatic cycles and represent a continuous risk of house infestation (Guhl et al, 2009). In addition, the residual effect of the insecticide seems to vary widely between studies (Gurevitz et al, 2012).The Casanare Department in the Orinoco region of Colombia (Figure 1), was subject to a control program led by the health authorities from 1997 to 2002. Entomological surveys were performed in several localities followed by fumigation with insecticide and were re-assessed for insects at different points in time.…”

Information to Act: Household Characteristics are Predictors of Domestic Infestation with the Chagas Vector Triatoma dimidiata in Central America

“…Repeated rounds of spraying could also lead to reduced susceptibility of insect populations to insecticides. 6 Since the description of Chagas disease, it has been known that rustic or deteriorated human domiciles provide conditions that allow triatomine infestation and colonization, 7 increasing the contact between humans and vectors and the risk of parasite transmission. Improving the domicile could provide long-term protection against the insect vectors by reducing infestation and preventing reinfestation.…”