Estudio de la prevalencia de la infección por Trypanosoma cruzi en zarigueyas (Didelphis albiventris) en Santiago del Estero, Argentina / Study of the prevalence of infection by Trypanosoma cruzi in opossums (Didelphis albiventris) in Santiago del Estero, Argentina

Entre los principales reservorios silvestres de Trypanosoma cruzi se encuentran las zarigueyas del género Didelphis, ampliamente distribuidas por el continente americano. En Amamá y Trinidad, Provincia de Santiago del Estero, Argentina, Didelphis albiventris es el marsupial más frecuente. Su población se renueva cada año y normalmente hay dos períodos reproductivos: uno a principios de la primavera y otro a principios del verano. Estas dos camadas son destetadas y abandonan la bolsa marsupial para incorporarse a la población, la primera (G1) a principios del verano y la segunda (G2) a principios del otoño. Entre 1988 y 1991 se estudiaron 409 individuos distintos de D. albiventris y los xenodiagnósticos revelaron que 35 por ciento de ellos estaban infectados por T.cruzi. Se observaron ciclos de renovación anual de la infección con prevalencias que oscilaron entre 22 y 43 por ciento. La adquisición del parásito ocurría a lo largo de todo el año, desde el verano hasta la primavera. La prevalencia de la infección aumentó con la edad. Los individuos G1 tuvieron tendencia a presentar mayores prevalencias que los G2, probablemente debido a un mayor tiempo de exposición a la transmisión. En las dos primeras categorías de edad, los individuos G2 mostraron mayores prevalencias que los G1, lo cual indica un aumento significativo de la intensidad de la transmisión durante el otoño. Las zarigueyas deberían considerarse como una fuente potencial de ingreso de T.cruzi al ciclo doméstico

Comparative meiotic studies in Triatoma sordida (Stal) and T. guasayana Wygodzinsky & Abalos (Reduviidae, Heteroptera)

Triatoma sordida and T. guasayana are competent Trypanosoma cruzi vectors, with overlapping distribution areas in Argentina. Both species are morphologically similar, and their immature stages are hard to discriminate. Cytogenetic studies in the genus Triatoma reveal scarce karyotypic variations, being 2n=20 + XY the most frequent diploid number in males. In the present work the meiotic behaviour of different Argentinian populations of T. sordida and T. guasayana has been analyzed; the meiotic karyotype of both species has also been compared. The species differ in total chromosome area and the relative area of the sex chromosomes. These meiotic karyotypic differences constitute an additional tool for the taxonomic characterization of T. sordida and T. guasayana. The analysis of an interpopulation hybrid of T. sordida (Brazil x Argentina) reveals a regular meiotic behaviour, despite the presence of heteromorphic bivalents. Our observations support the hypothesis that karyotype variatons through the gain or loss of heterochromatin can not be considered as a primary mechanism of reproductive isolation in Triatoma.

Interaction between Didelphis albiventris and Triatoma infestans in relation to Trypanosoma cruzi transmission

This paper attempts to prove if a high Trypanosoma cruzi prevalence of opossums might be reached with few potential infective contacts. One non-infected Didelphis albiventris to T. cruzi and 10 infected nymphs of Triatoma infestans were left together during 23 hr in a device that simulated a natural opossum burrow. Twenty-six replicates were perfomed using marsupials and triatomines only once. Potentially infective contacts occurred in all the trials. From the 26 opossums used in trials, 54 por cento did not eat any bug. Of the 260 bugs used, 21 por cento were predated. In the 25 trials involving 205 surving bugs, 36 por cento of them did not feed. In 15/25 cases, maior ou igual a 60 por cento of the triatomines were able to feed. The parasitological follow-up of 24 opossums showed that among 10 that had eaten bugs, 4 turned out infected and among the 14 that had not predate, 3 (21 por cento) became positive. In sum, 7/24 (29 por cento) of the marsupials acquired the infection after the experiment. This infection rate was similar to the prevalences found for the opossum population of Santiago del Estero, Argentina, suggesting that the prevalences observed in the field might be reached if each marsupial would encounter infected bugs just once in its lifetime.

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.