The eco-epidemiology of Triatoma infestans in the temperate Monte Desert ecoregion of mid-western Argentina

BACKGROUND The eco-epidemiological status of Chagas disease in the Monte Desert ecoregion of western Argentina is largely unknown. We investigated the environmental and socio-demographic determinants of house infestation with Triatoma infestans, bug abundance, vector infection with Trypanosoma cruzi and host-feeding sources in a well-defined rural area of Lavalle Department in the Mendoza province. METHODS Technical personnel inspected 198 houses for evidence of infestation with T. infestans, and the 76 houses included in the current study were re-inspected. In parallel with the vector survey, an environmental and socio-demographic survey was also conducted. Univariate risk factor analysis for domiciliary infestation was carried out using Firth penalised logistic regression. We fitted generalised linear models for house infestation and bug abundance. Blood meals were tested with a direct ELISA assay, and T. cruzi infection was determined using a hot-start polymerase chain reaction (PCR) targeting the kinetoplast minicircle (kDNA-PCR). FINDINGS The households studied included an aged population living in precarious houses whose main economic activities included goat husbandry. T. infestans was found in 21.2% of 198 houses and in 55.3% of the 76 re-inspected houses. Peridomestic habitats exhibited higher infestation rates and bug abundances than did domiciles, and goat corrals showed high levels of infestation. The main host-feeding sources were goats. Vector infection was present in 10.2% of domiciles and 3.2% of peridomiciles. Generalised linear models showed that peridomestic infestation was positively and significantly associated with the presence of mud walls and the abundance of chickens and goats, and bug abundance increased with the number of all hosts except rabbits. MAIN CONCLUSIONS We highlight the relative importance of specific peridomestic structures (i.e., goat corrals and chicken coops) associated with construction materials and host abundance as sources of persistent bug infestation driving domestic colonisation. Environmental management strategies framed in a community-based programme combined with improved insecticide spraying and sustained vector surveillance are needed to effectively suppress local T. infestans populations.

A motorized vehicle-mounted sprayer as a new tool for Chagas disease vector control / Equipamiento aspersor montado en vehículos como nueva herramienta para el control vectorial de la enfermedad de Chagas / Equipamento aspersor montado em veículo como ferramenta nova para o controle vetorial da doença de Chagas

Abstract: Residual insecticide spraying still is the main tool used to suppress house infestations with Chagas disease vectors. While manual compression sprayers (MCS) have traditionally been used in Latin America, Mendoza's vector control program from Argentina introduced the use of a modified motorized vehicle-mounted sprayer (VMS) with apparent advantages over MCS. We conducted a randomized intervention trial to evaluate the effectiveness and selected components of the performance of MCS and VMS. We assessed house infestation by Triatoma infestans in 76 previously-infested houses at 0, 1, 4 and 12 months postintervention. Infestations were reduced substantially, with no significant differences between treatments. End-point infestations were restricted to peridomiciles. Although VMS required less time to complete the house spraying than MCS, both treatments had similar performance and did not suppress infestations completely. The main relative advantages of VMS were a reduced physical effort, especially under harsh field conditions, and potential gains in spray coverage per unit of time.

Resumen: El empleo de insecticida residual es todavía la principal herramienta para suprimir la infestación domiciliaria por triatominos, vectores de la enfermedad de Chagas. Mientras los aspersores manuales activados por compresión han sido utilizados tradicionalmente en América Latina, el programa de control vectorial de la provincia de Mendoza, Argentina, introdujo el uso de un equipamiento aspersor montado en un vehículo, aparentemente con ventajas respecto al aspersor manual. Realizamos un ensayo de intervención aleatorizado para evaluar la efectividad y los componentes seleccionados del desempeño de los dos equipamientos. Evaluamos la infestación por Triatoma infestans en 76 vivendas, previamente infestados a 0, 1, 4 y 12 meses tras la intervención. Las infestaciones se redujeron substancialmente, sin diferencia significativa entre las dos técnicas. Las infestaciones finales se limitaban al peridomicilio. El equipamiento montado en el vehículo llevaba menos tiempo para completar la aplicación, comparado con el equipamiento manual, pero los dos tratamientos tuvieron un desempeño semejante y dejaron de suprimir completamente las infestaciones. Las principales ventajas del equipamiento montado en vehículo fueron: la reducción del esfuerzo físico, principalmente en condiciones adversas en el campo, y potenciales beneficios en términos de cobertura de pulverización por unidad de tiempo.

Resumo: A aplicação de inseticida residual ainda é a principal medida para suprimir a infestação domiciliar por triatomíneos, vetores da doença de Chagas. Enquanto os aspersores manuais acionados por compressão têm sido utilizados tradicionalmente na América Latina, o programa de controle vetorial da Província de Mendoza, Argentina, introduziu o uso de um equipamento aspersor montado em veículo, aparentemente com vantagem em relação ao aspersor manual. Realizamos um estudo randomizado de intervenção para avaliar a efetividade e os componentes selecionados do desempenho dos dois equipamentos. Avaliamos a infestação por Triatoma infestans em 76 domicílios previamente infestados a 0, 1, 4 e 12 meses pós-intervenção. As infestações foram reduzidas substancialmente, sem diferença significativa entre as duas técnicas. As infestações finais eram limitadas ao peridomicílio. O equipamento montado em veículo levava menos tempo para completar a aplicação, comparado com o equipamento manual, mas os dois tratamentos tiveram desempenho semelhante e deixaram de suprimir completamente as infestações. As principais vantagens do equipamento montado em veículo foram redução do esforço físico, principalmente em condições adversas em campo, e potenciais ganhos em termos de cobertura de borrifação por unidade de tempo.

Where do these bugs come from? Phenotypic structure of Triatoma infestans populations after control interventions in the Argentine Chaco

House re-invasion by native triatomines after insecticide-based control campaigns represents a major threat for Chagas disease vector control. We conducted a longitudinal intervention study in a rural section (Area III, 407 houses) of Pampa del Indio, northeastern Argentina, and used wing geometric morphometry to compare pre-spray and post-spray (re-infestant bugs) Triatoma infestans populations. The community-wide spraying with pyrethroids reduced the prevalence of house infestation by T. infestans from 31.9% to < 1% during a four-year follow-up, unlike our previous studies in the neighbouring Area I. Two groups of bug collection sites differing in wing shape variables before interventions (including 221 adults from 11 domiciles) were used as a reference for assigning 44 post-spray adults. Wing shape variables from post-spray, high-density bug colonies and pre-spray groups were significantly different, suggesting that re-infestant insects had an external origin. Insects from one house differed strongly in wing shape variables from all other specimens. A further comparison between insects from both areas supported the existence of independent re-infestation processes within the same district. These results point to local heterogeneities in house re-infestation dynamics and emphasise the need to expand the geographic coverage of vector surveillance and control operations to the affected region.