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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 because of enhanced resistance or tolerance and determine appropriate responses.

SUBMITTER: Gurevitz JM

PROVIDER: S-EPMC3760256 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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Unexpected failures to control Chagas Disease vectors with pyrethroid spraying in northern Argentina.

Gurevitz Juan M JM Gaspe María Sol MS Enríquez Gustavo F GF Vassena Claudia V CV Alvarado-Otegui Julián A JA Provecho Yael M YM Cueto Gastón A Mougabure GA Picollo María Inés MI Kitron Uriel U Gürtler Ricardo E RE

Journal of medical entomology 20121101 6

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 po ...[more]

PMID: 23270166

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Project description:BackgroundTriatoma infestans-mediated transmission of Tripanosoma cruzi, the causative agent of Chagas disease, remains as a major health issue in southern South America. Key factors of T. infestans prevalence in specific areas of the geographic Gran Chaco region-which extends through northern Argentina, Bolivia, and Paraguay-are both recurrent reinfestations after insecticide spraying and emerging pyrethroid-resistance over the past ten years. Among alternative control tools, the pathogenicity of entomopathogenic fungi against triatomines is already known; furthermore, these fungi have the ability to fully degrade hydrocarbons from T. infestans cuticle and to utilize them as fuel and for incorporation into cellular components.Methodology and findingsHere we provide evidence of resistance-related cuticle differences; capillary gas chromatography coupled to mass spectrometry analyses revealed that pyrethroid-resistant bugs have significantly larger amounts of surface hydrocarbons, peaking 56.2+/-6.4% higher than susceptible specimens. Also, a thicker cuticle was detected by scanning electron microscopy (32.1+/-5.9 microm and 17.8+/-5.4 microm for pyrethroid-resistant and pyrethroid-susceptible, respectively). In laboratory bioassays, we showed that the virulence of the entomopathogenic fungi Beauveria bassiana against T. infestans was significantly enhanced after fungal adaptation to grow on a medium containing insect-like hydrocarbons as the carbon source, regardless of bug susceptibility to pyrethroids. We designed an attraction-infection trap based on manipulating T. infestans behavior in order to facilitate close contact with B. bassiana. Field assays performed in rural village houses infested with pyrethroid-resistant insects showed 52.4% bug mortality. Using available mathematical models, we predicted that further fungal applications could eventually halt infection transmission.ConclusionsThis low cost, low tech, ecologically friendly methodology could help in controlling the spread of pyrethroid-resistant bugs.

Project description:BackgroundWhere resources are available, non-pyrethroid IRS can be deployed to complement standard pyrethroid LLINs with the aim of achieving improved vector control and managing insecticide resistance. The impact of the combination may however depend on the type of IRS insecticide deployed. Studies comparing combinations of pyrethroid LLINs with different types of non-pyrethroid IRS products will be necessary for decision making.MethodsThe efficacy of combining a standard pyrethroid LLIN (DuraNet®) with IRS insecticides from three chemical classes (bendiocarb, chlorfenapyr and pirimiphos-methyl CS) was evaluated in an experimental hut trial against wild pyrethroid-resistant Anopheles gambiae s.l. in Cové, Benin. The combinations were also compared to each intervention alone. WHO cylinder and CDC bottle bioassays were performed to assess susceptibility of the local An. gambiae s.l. vector population at the Cové hut site to insecticides used in the combinations.ResultsSusceptibility bioassays revealed that the vector population at Cové, was resistant to pyrethroids (<20% mortality) but susceptible to carbamates, chlorfenapyr and organophosphates (≥98% mortality). Mortality of wild free-flying pyrethroid resistant An. gambiae s.l. entering the hut with the untreated net control (4%) did not differ significantly from DuraNet® alone (8%, p = 0.169). Pirimiphos-methyl CS IRS induced the highest mortality both on its own (85%) and in combination with DuraNet® (81%). Mortality with the DuraNet® + chlorfenapyr IRS combination was significantly higher than each intervention alone (46% vs. 33% and 8%, p<0.05) demonstrating an additive effect. The DuraNet® + bendiocarb IRS combination induced significantly lower mortality compared to the other combinations (32%, p<0.05). Blood-feeding inhibition was very low with the IRS treatments alone (3-5%) but increased significantly when they were combined with DuraNet® (61% - 71%, p<0.05). Blood-feeding rates in the combinations were similar to the net alone. Adding bendiocarb IRS to DuraNet® induced significantly lower levels of mosquito feeding compared to adding chlorfenapyr IRS (28% vs. 37%, p = 0.015).ConclusionsAdding non-pyrethroid IRS to standard pyrethroid-only LLINs against a pyrethroid-resistant vector population which is susceptible to the IRS insecticide, can provide higher levels of vector mosquito control compared to the pyrethroid net alone or IRS alone. Adding pirimiphos-methyl CS IRS may provide substantial improvements in vector control while adding chlorfenapyr IRS can demonstrate an additive effect relative to both interventions alone. Adding bendiocarb IRS may show limited enhancements in vector control owing to its short residual effect.

Project description:INTRODUCTION: Ninety percent of the aboriginal communities of Argentina are located in areas of endemic vectorial transmission of Chagas disease. Control activities in these communities have not been effective. The goal of this research was to explore the role played by beliefs, habits, and practices of Pilaga and Wichi indigenous communities in their interaction with the local health system in the province of Formosa. This article contributes to the understanding of the cultural barriers that affect the communication process between indigenous peoples and their health care providers. METHODS: Twenty-nine open ended interviews were carried out with members of four indigenous communities (Pilaga and Wichi) located in central Formosa. These interviews were used to describe and compare these communities' approach to health and disease as they pertain to Chagas as well as their perceptions of Western medicine and its incarnation in local health practice. RESULTS: Five key findings are presented: 1) members of these communities tend to see disease as caused by other people or by the person's violation of taboos instead of as a biological process; 2) while the Pilaga are more inclined to accept Western medicine, the Wichi often favour the indigenous approach to health care over the Western approach; 3) members of these communities do not associate the vector with the transmission of the disease and they have little awareness of the need for vector control activities; 4) indigenous individuals who undergo diagnostic tests and accept treatment often do so without full information and knowledge; 5) the clinical encounter is rife with conflict between the expectations of health care providers and those of members of these communities. CONCLUSION: Our analysis suggests that there is a need to consider the role of the cultural patterning of health and disease when developing interventions to prevent and control Chagas disease among indigenous communities in Northern Argentina. This is especially important when communicating with these communities about prevention and control. These research findings might also be of value to national and provincial agencies in charge of decreasing the rates of Chagas disease among indigenous populations.

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Unexpected failures to control Chagas Disease vectors with pyrethroid spraying in northern Argentina.

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Unexpected failures to control Chagas Disease vectors with pyrethroid spraying in northern Argentina.

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