The opossum of the genus Didelphis is one of the principal wild reservoirs of Trypanosoma cruzi and is widely distributed in the Western Hemisphere. Didelphis albiventris is the most common marsupial in Amamá and Trinidad, two communities in the province of Santiago del Estero, Argentina. The D. albiventris population is replaced every year, and the opossum normally has two reproductive periods, one at the beginning of the spring and another at the beginning of the summer. The two litters are weaned, and they leave the mother's marsupial pouch to join the population, the first (G1) at the beginning of the summer and the second (G2) at the beginning of the fall. Between 1988 and 1991 409 D. albiventris opossums were studied, and xenodiagnoses showed that 35% of them were infected with T. cruzi. Annual cycles of renewed infection were observed, with prevalences that ranged between 22% and 43%. The acquisition of the parasite occurred over the entire year, from the summer through the spring. The prevalence of infection increased with age. The G1 individuals tended to present higher prevalences than the G2 individuals, probably from being exposed to transmission for a longer period of time. In the first two (younger) age categories for the opossums, G2 individuals showed higher prevalences than did the G1 individuals. This indicates a significant increase in transmission intensity during the fall. Opossums should be regarded as a potential source of T. cruzi entry to the domestic transmission cycle.

Entre los principales reservorios silvestres de Trypanosoma cruzi se encuentran las zarigüeyas 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% de ellos estaban infectados por T. cruzi. Se observaron ciclos de renovación anual de la infección con prevalencias que oscilaron entre 22 y 43%. 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 zarigüeyas deberían considerarse como una fuente potencial de ingreso de T. cruzi al ciclo doméstico.

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% did not eat any bug. Of the 260 bugs used, 21% were predated. In the 25 trials involving 205 surving bugs, 36 % of them did not feed. In 15/25 cases, maior ou igual a 60% 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%) became positive. In sum, 7/24 (29%) 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.

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.