Entomological aspects of Chagas' disease transmission in the domestic habitat, Argentina

OBJETIVO: Estudiar el riesgo doméstico de transmisión de Trypanosoma cruzi por medio de un indicador entomológico y analizar su relación con características culturales y de las viviendas. MÉTODOS: Se estudiaron 158 casas en el área endémica argentina. Cada vivienda infestada se clasificó de acuerdo con un indicador entomológico de riesgo (número de picadas riesgosas/ humano). Mediante encuestas se evaluaron factores de riesgo asociados a la vivienda y habitos de los moradores. RESULTADOS: Las casas infestadas mostraron un rango amplio de valores de riesgo (0 a 5 picadas riesgosas/ humano). Se observó un gran número de viviendas con bajos valores de riesgo y pocas viviendas con valores elevados. El 44 por ciento de las Triatoma infestans colectadas estaban alimentadas sobre ser humano y el 27 por ciento sobre perro o gallina. Las viviendas donde perros y/o gallinas compartían la habitación humana, tuvieron valores de riesgo más elevados. Las viviendas ordenadas y limpias exhibieron bajos valores, debido a un escaso número de T. infestans. Se comprobó un 24.3 por ciento de correlación entre el tiempo transcurrido luego de aplicar insecticidas y el número de vectores en la vivienda. Sin embargo, no hubo correlación entre el tiempo post-rociado y la infectividad de T. infestans. Se observó correlación entre los valores del indicador entomológico y la seroprevalencia en niños. CONCLUSIONES: El riesgo de transmisión de T. cruzi en cada vivienda, medido a través de un indicador entomológico, se correlaciona positivamente con la prevalencia de seropositividad en niños y con hábitos de los moradores.

Changes associated with laboratory rearing in antennal sensilla patterns of Triatoma infestans, Rhodnius prolixus, and Rhodnius pallescens (Hemiptera, Reduviidae, Triatominae)

We examined changes in the array of antennal sensilla of three species of Triatominae (Triatoma infestans, Rhodnius prolixus, and R. pallescens) following their establishment for different periods in laboratory culture. In each case, the laboratory colonies were compared with conspecific samples taken directly from the field, by quantitative analysis of the sensilla arrays on the three distal segments of the antenna in terms of the densities of three types of chemoreceptors (basiconics and thick and thin walled trichoids) and one type of mechanoreceptor (bristles). Sensilla densities were compared by ANOVA or non-parametric tests, and by multivariate discriminant analysis. Strains of the same species reared in different laboratories showed significant differences in their sensilla arrays, especially when compared to field-collected material from the same geographic origin. A Bolivian strain of T. infestans reared in the laboratory for 15 years and fed at monthly intervals, showed greatest differences from its conspecific wild forms, especially in terms of reductions in the number of chemoreceptors. By contrast, an Argentine strain of T. infestans reared for 25 years in the laboratory and fed weekly, showed a relative increase in the density of mechanoreceptors. A Colombian strain of R. prolixus reared for 20 years and fed weekly or fortnightly, showed only modest differences in the sensilla array when compared to its wild populations from the same area. However, a Colombian strain of R. pallescens reared for 12 years and fed fortnightly, did show highly significant reductions in one form of chemoreceptor compared to its conspecific wild populations. For all populations, multivariate analysis clearly discriminated between laboratory and field collected specimens, suggesting that artificial rearing can lead to modifications in the sensory array. This not only supports the idea of morphological plasticity in these species, but also suggests caution in the use of long-established laboratory material for experimental studies designed to extrapolate the natural behaviour and physiology of these species.

Feeding and defaecation patterns in Triatoma sordida

Triatoma sordida is a peridomestic Triatominae that could play an important role in the transmission of Trypanosoma cruzi, although its vectorial competence is not well known. The aim of this work was to evaluate two aspects of the vectorial competence: the feeding behaviour and defaecation patterns, and to compare them with T. infestans. The feeding and defaecation patterns were studied in adults and fifth instar nymphys of T. sordida fed ad libitum on a restrained pigeon. The results showed how the blood meal size control excretion behaviour. Blood intake and time to first defaecation showed a significant negative correlation. Adults and nymphs frequently defaecated during the blood meal, reaching the maximum frequency within the first 10 minutes.

Are dead Triatoma infestans a competent vector of Trypanosoma cruzi?

After Triatoma infestans death, Trypanosoma cruzi survived several days, maintaining the ability to infect a vertebrate host. Dead bugs from an endemic area collected during an official spraying comapign showed mobile rectal tripanosomes up to 14 days after vector death. Two days after vector death2, 760 tripomastigotes were found alive in its rectal material. However, the number of mobile tripomastigotes decreased significantly from the 5th day after death. Laboratory proofs with third and fifth nymphal stage showed similar results. Living tripanosomes were found in their rectal material at 10 days in third stage and even at 30 days in fifth nymphal stage. The mean number of tripomastigotes had no changes up to 10 days in third nymphal stage and increased significantly from 1 to 10 days in the fifth stage. Conjuctival instillation as well as intraperitoneal innoculation to mice, of metacyclic forms from dead T. infestans produced infection in the vertebrate host. Present results show that human contact with dead vector highly probable in summer and living and infective T. cruzi are available for transmision in the vector