RESUMO
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.
Assuntos
Doença de Chagas/epidemiologia , Gambás , Animais , Argentina/epidemiologia , PrevalênciaRESUMO
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 in 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 variations through the gain or loss of heterochromatin can not be considered as a primary mechanism of reproductive isolation in Triatoma.
Assuntos
Triatominae/genética , Animais , Argentina , Mapeamento Cromossômico , Cariotipagem , Masculino , Meiose/genética , Cromossomos Sexuais/genética , Espermatogênese/genética , Triatoma/classificação , Triatoma/citologia , Triatoma/genética , Triatominae/classificação , Triatominae/citologiaRESUMO
In the study area Triatoma guasayana Wygodzinsky & Abalos is the only wild triatomine found sympatric with Triatoma infestans (Klug) in peridomestic premises. The Trypanosoma cruzi Chagas wild cycle is centered around the same biotopes occupied by T. guasayana, which are also visited mainly by opossums with annual prevalences of 29-50%. Twelve hectares were sampled for 4 consecutive years during all seasons. During that time, 420 T. Guasayana individuals were collected in 11.3% of 1,188 biotopes of 4 types, which included quimiles (the cactus Opuntia quimilo), chaguares (several species of bromeliads), trees, and logs. Quimiles had the highest percentage of positive biotopes (31.5%) followed by chaguares (22.3%), whereas 5% of the logs were found infested. During all seasons, 9.6-15.2% of biotopes were found infested. Distance to artificial biotopes was not statistically significant when comparing the frequency of triatomine numbers per biotope in all biotope-season combinations. With the exception of quimiles in the fall, the mean number of triatomines was higher in chaguares during all seasons. Triatomine abundance by biotope and season strata showed a clumped distribution, except for the quimiles biotope during the summer. When pooling by seasons, the mean number of triatomines in chaguares and quimiles biotope was higher than in logs and trees, with all biotopes showing a strong clumped distribution. When pooling by biotopes, the mean number of T. guasayana was relatively similar for all seasons, with a strong clumped distribution. The strong contagious distribution of T. guasayana in the hardwood forest biotopes may explain the maintenance of the wild cycle of T. cruzi, despite the low number and the low prevalences of the insect vector.
Assuntos
Triatoma , Animais , Argentina , Demografia , Feminino , Humanos , Masculino , Estações do AnoRESUMO
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 performed 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 surviving bugs, 36% of them did not feed. In 15/25 cases, > or = 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.
Assuntos
Doença de Chagas/transmissão , Gambás/parasitologia , Triatoma/parasitologia , Trypanosoma cruzi/fisiologia , Animais , ArgentinaRESUMO
Success in obtaining a blood meal and rapid access to hiding places after feeding are the principal requirements triatomines have as they colonize artificial ecotopes. Feeding success and postfeeding location of 3rd and 5th instars of Triatoma sordida (Stål), of T. guasayana Wygodzinsky & Abalos, and T. infestans (Klug) were studied in an experimental box in which triatomines and a chicken were left to interact overnight. The bird was enclosed in a glass cube, slightly raised to allow triatomines to get in and out, turning the space outside into an extensive refuge area. Four bunches of dry corn husks and a wooden panel were also offered as shelters. The number of live and dead insects and their locations at the end of the experiment were recorded. Predation--as the percentage of missing insects--and success--as the percentage of insects alive and fed--were calculated. Interactions with the host were different among species and sometimes also between individuals of different life stages of the same species. Predation was always > 20%. T. sordida was the best exploiter of the blood source, because 3rd instars were more successful and 5th instars were as successful as the corresponding T. infestans stages. Performance of T. guasayana was equivocal because survival and feeding success were different for both instars. T. infestans showed a pronounced tendency to climb, and 3rd instars of T. guasayana were equally distributed in the upper half of the box and in the corn husks, whereas the majority of T. sordida and 5th instars of T. guasayana sheltered in the husks.
Assuntos
Triatoma , Animais , Galinhas/parasitologia , Comportamento Alimentar , Feminino , MasculinoRESUMO
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.