Effects of non-susceptible hosts on the infection with Trypanosoma cruzi of the vector Triatoma infestans: an experimental model

We tested experimentally the effects of the presence of non-susceptible hosts on the infectin with Trypanosoma cruzi of the vector Triatoma infestans. The experiment consisted in two treatments: with chickens, including two chickens (non-susceptible hosts) and two infected guinea pigs (susceptible hosts), and without chickens, including only two infected guinea pigs. The hosts were held unrestrained in individual metal cages inside a closed tulle chamber. A total of 200 uninfected T. infestand third instar nymphs were liberated in each replica, collected on day 14, and examined for infection and blood meal sources on day 32-36. The additional presence of chickens relative to infected guinea pigs: (a) significantly modified the spatial distribution of bugs; (b) increased significantly the likelihoods of having a detectable blood meal on any host and molting to the next instar; (c) did not affect the bugs ' probability of death by predation; and (d) decreased significantly the overall percentage of T. infestand infected with T. cruzi. The bugs collected from inside or close to the guinea pigs ' cages showed a higher infection rate (71-88 por cento) than those collected from the chickens ' cages (22-32 por cento). Mixed blood meals on chickens and guinea pigs were detedted in 12-21 por cento of bugs. Although the presence of chickens would decrease the overall percentage of infected bugs in short term experiments, the high rate of host change of T. infestans would make this difference fade out if longer exposure times had been provided.

Trypanosoma cruzi infection in Triatoma infestans and other triatomines: long-term effects of a control program in rural northwestern Argentina / Infección por Trypanosoma cruzi en Triatoma infestans y otros triatómidos: efectos a largo plazo de un programa de control en una zona rural del noroeste de Argentina

The prevalence of Trypanosoma cruzi infection in Triatoma infestans, Triatoma guasayana, and Triatoma sordida was evaluated in Amamá and other neighboring rural villages in northwestern Argentina for five years after massive spraying with deltamethrin in 1992 and selective sprays thereafter. Local residents and expert staff collected triatomines in domiciliary and peridomestic sites. During 1993-1997, the prevalence of T.cruzi was 2.4 per cent in 664 T. infestans, 0,7 per cent in 268 T.guasayana, and 0.2 per cent in 832 T.sordida. T.cruzi infection was more frequently detected in adult bugs and in triatomines collected at domiciliary sites. The infected T.guasayana and T.sordida were nymphs and adults, respectively, captured at peridomestic sites. The prevalence of T.cruzi infection in T.infestans decreased from 7.7 per cent to 1.5 per cent during the surveillance period, although that change was not statistically significant. Comparison of T.infestans infection rates before the control program and during surveillance showed a highly significant decrease from 49 per cent to 4.6 per cent in bedrooms, as well as a fall from 6 per cent to 1.8 per cent in peridomestic sites. Because of its infection with T.cruzi and frequent invasion of domiciliary areas and attacks on humans and dogs, T. guasayana appeared implicated as a putative secondary vector of T.cruzi in domestic and peridomestic sites during the surveillance period.T. sordida was the most abundat species, but it was strongly associated with chickens and showed little tendency to invade bedrooms

Durante los cinco años posteriores a una fumigación masiva con deltametrina realizada en 1992 y seguida de fumigaciones selectivas, se investigó la prevalencia de la infección por Trypanosoma cruzi en Triatoma infestans, Triatoma guasayana y Triatoma sordida en Amamá y otras poblaciones rurales vecinas del noroeste de Argentina. Los triatómidos fueron recogidos en los domicilios y en el área peridoméstica por los propios residentes y por personal experto. Durante el quinquenio 1993­1997, la prevalencia de T. cruzi fue de 2,4% en 664 T. infestans, de 0,7% en 268 T. guasayana y de 0,2% en 832 T. sordida. La infección por T. cruzi se detectó con mayor frecuencia en las chinches adultas y en los triatómidos recogidos en los domicilios. T. guasayana y T. sordida fueron, respectivamente, ninfas y adultos recogidos en el área peridoméstica. Durante el período de vigilancia, la prevalencia de la infección por T. cruzi en T. infestans disminuyó de 7,7% en 1993 a 1,5% en 1997, aunque este cambio no fue estadísticamente significativo. La comparación de las tasas de infección de T. infestans antes del programa de control (1992) y durante el período de vigilancia (1993­1997) reveló una disminución altamente significativa, de 49% a 4,6%, en los dormitorios y también en las áreas peridomésticas (de 6% a 1,8%). Debido a su infección por T. cruzi y a su frecuente invasión de las áreas domésticas con ataques a los humanos y a los perros, T. guasayana parecía estar implicado como vector secundario de T. cruzi en las áreas domésticas y peridomésticas durante el período de vigilancia. T. sordida fue la especie más abundante, pero estaba estrechamente asociada a los pollos y mostró escasa tendencia a invadir los dormitorios

The role of the peridomiciliary area in the elimination of Triatoma infestants from rural Argentine communities / El papel del peridomicilio en la eliminación de Triatoma infestans de comunidades rurales argentinas

El objetivo del estudio fue identificar el origen y estudiar la dinámica de la reinfestación por Triatoma infestans ocurrida después de rociar con deltametrina el domicilio y peridomicilio de 94 casas de tres comunidades rurales el noroeste argentino. La efectividad del rociamiento se evaluó inmediatamente después y al segundo mes de rociar las viviendas. Además, se detectaron y rociaron 5 focos residuales peridomiciliarios y 3 preexistentes que no habían sido rociados. Para monitorizar la reinfestación, se colocaron biosensores en los domicilios, se solicitó a cada familia que capturase triatominos y los guardara en bolsas de plástico, y se buscaron triatominos en domicilios y peridomicilios usando un aerosol para desalojar a los insectos de sus refugios. Solo se realizaron rociamientos selectivos donde se encontró alguna colonia de T. infestans. Durante 30 meses de seguimiento, el porcentaje de casas donde se capturó algún T. infestans osciló entre 3% y 9%. En 6 casas se capturaron T. infestans en más de una evaluación. El número de peridomicilios infestados (19) fue el doble que el de domicilios (9). Solo se detectaron colonias de T. infestans en peridomicilios. La cifra de T. infestans capturados en peridomicilios fue seis veces más alta que la de los domicilios. Las gallinas fueron el hospedador más frecuentemente asociado con los focos peridomiciliarios. El peridomicilio constituyó el origen y la principal fuente de reinfestación. Para reducir la velocidad de reinfestación y la frecuencia de rociamientos es preciso combinar medidas de manejo ambiental y control químico en los peridomicilios: reducir los refugios para triatominos; restringir la cría de aves a estructuras no colonizables por triatominos; aplicar un insecticida menos degradable por agentes climáticos o realizar un segundo rociamiento de 6 a 12 meses después del primero, y emplear un dispositivo para detectar tempranamente la presencia de T. infestans en peridomicilios

The purpose of this study was to identify the origin of Triatoma infestans reinfestation and study its dynamics following spraying with deltamethrin inside and around 94 houses in three rural communities in northwestern Argentina. The effectiveness of the spraying was evaluated immediately after the houses were sprayed and two months later. In addition, five residual peridomiciliary foci were found and sprayed, as well as three preexisting ones that had not been sprayed. To monitor reinfestation, biosensors were placed in the houses and each family was also asked to capture triatomines and keep them in plastic bags; in addition, triatomines were searched for in and around houses, using an aerosol that dislodged them from their hiding places. Selective sprayings were carried out only where a colony of T. infestans was found. During the 30 months of follow-up, the percentage of houses in which any T. infestans were captured varied between 3% and 9%. In six houses, T. infestans were captured during more than one evaluation. The number of peridomiciliary areas found to be infested (19) was double the number of infested houses (9). Colonies of T. infestans were found only in the peridomiciliary areas, where the number of T. infestans captured was six times higher than in the houses. Chickens were the host most frequently associated with peridomiciliary foci. This area was the origin and principal source of reinfestation. To reduce the speed of reinfestation and the frequency with which sprayings are needed, the following environmental and chemical control methods must be combined in the peridomiciliary area: reduce the number of hiding places of triatomines; restrict the raising of birds to structures that cannot be colonized by triatomines; apply an insecticide that is less likely to be degraded by exposure to the elements, or perform a second spraying 6 to 12 months after the first; and employ a device for early detection of the presence of T. infestans around houses.

The interaction between poultry and Triatoma infestans Klug, 1834 (Hemiptera: Reduviidae) in an experimental model

This paper compares the predation pressure that ducks and chickens exert on triatomines. For the tests, these birds were placed in individual boxes together with a known number of Triatoma infestans and left to interact from 6 p.m. till the next morning, involving a long lasting period of complete darkness limited by two short-term periods of semi-darkness. There was a shelter which could prevent the bugs from being predated. The number of live and dead triatomines was recorded, considering missing bugs as predated by the birds. Ducks exhibited a greater predatory activity than chickens, that could be due to a long term active period at night while chickens sleep motionless from sunset to dawn. Surviving triatomines that had fed on chickens outnumbered those fed on ducks suggesting that these were less accessible to the triatomine biting. If ducks are better than chickens to detect and eat bugs and to interfere with their feeding in the field, an increase in duck number might help to diminish triatomine density. Further research is needed to determine the feasibility of application of these experimental results.

América Central / Central America

Se dan datos breves sobre cada una de las dieciséia especies de triatominos existentes en seis países de América Central (Guatemala, Honduras, El Salvador, Nicaragua, Costa Rica y Panamá), relativos a su distribución goegráfica, hábitats en que son halladas y, en algunos casos, su grado de infección por Trypanosoma cruzi. Se trata de: Belminus costaricensis; Belminus herreri; Microtriatoma trinidadensis; Cavernicola pilosa; Rhodnius pallescens; Rhodnius pictipes; Rhodnius prolixus; Eratyrus cuspidatus; Panstrongylus geniculatus; Panstrongylus humeralis; Panstrongylus rufotuberculatus; Triatoma dimidiata; Triatoma diapar; Triatoma nitida; Triatoma ryckmani; y, Triatoma venosa. Se mencionan como hospederos de Trypanosoma cruzi en la región, a perros, gatos, marsupiales y roedores

Perú / Peru

Se describe la distribución geográfica y la ecología (hábitats) de 19 especies de tratominos existentes en Perú: Belminus peruvianus, Microtriatoma trinidadensis, Cavernicola pilosa, Rhodnius ecuadoriensis, Rhodnius robustus, Rhodnius pictipes, Eratyrus mucronatus, Eratyrus cuspidatus, Panstrongylus herreri, Panstrongylus chinai, Panstrongylus geniculatus, Panstrongylus rufotuberculatus, Triatoma dimidiata, Triatoma carrioni, Triatoma infestans; y se mencionan otras dos especies (panstrongylus lignarius, y Triatoma venosa), como de presencia dudosa o no confirmada. Se identifican como reservorios de Trypanosoma cruzi a cobayos, perros, gatos, conejos y cerdos; y, entre los mamíferos silvestres, a marsupiales, monos, murciélagos, citándose para cada especie los respectivos porcentajes de infección por T. cruzi