RESUMEN

Triatoma guasayana is a silvatic triatomine species distributed in Argentina, Bolivia and Paraguay. The study was performed in a secondary forest of Santiago del Estero, Argentina. The abundance of T. guasayana was evaluated by census in the following wild biotopes: quimiles (Opuntia quimilo), chaguares (dry bromeliads), logs and underground burrows. Ten biotopes of each type were dismantled in winter (August) and another 40 in summer (January); all fauna was recorded. The biotopes most infested by T. guasayana were quimiles (65%), followed by chaguares (55%), and logs (25%). Quimiles and chaguares were infested in both seasons, whereas logs were positive only in summer and burrows were never infested. Infestation and abundance were higher in summer than in winter. The biotope structure is a key factor for T. guasayana colonization. The larger number of refuges, the constant presence of blood sources and suitable inner microclimatic conditions offered by quimiles may favour the persistence of T. guasayana colonies. The richness of invertebrate fauna per type of biotope was ranked in the same order as that of T. guasayana, suggesting similar microhabitat requirements for all studied arthropods.

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Sylvatic triatomines might use the peridomicile as a 1st step in the process of domiciliation. Therefore, we evaluated the capability of sylvatic species to colonize the peridomicile of a rural area in the Province of Santiago del Estero, Argentina. The research was carried out in 6 houses in the village of Trinidad. The person per hour capture method was employed to determine the presence of triatomines in all the buildings (n = 44). Dispersing adults were collected by means of light traps and by villagers when approaching their houses. Triatoma infestans (Klug) was the most abundant species followed by the sylvatic Triatoma guasayana Wygodzinsky & Abalos. The branch pens, which included cacti, Opuntia quimilo, and bromeliads in their structure, were significantly associated with T. guasayana. Most of these insects had fed on domestic blood sources. With the exception of 1 Triatoma sordida (Stål), dispersing adults were T. guasayana; among those approaching houses, 12 were females (2 of which were infected with Trypanosoma cruzi Chagas) and 3 were males. T. guasayana was found to be capable of intensively invading the intradomicile and the peridomicile, showing a high tendency to settle in the ecotopes which included nontransformed raw material from the wild and where T. infestans was less abundant.

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An association was determined between Triatona infestans, poultry, and humans in Trinidad, in the Province of Santiago del Estero, Argentina. To collect triatomines, four samples were taken at the area immediately surrounding six houses by the one hour/man capture method (December 1991 - October 1992). Peridomiciliary ecotopes were classified as arthropic (where humans carry out daily activities) or non-anthropic. Tratomine feeding habits were also determined. Of 134 biotopes, 21% had T. infestans, 22% had poultry, and 54% were anthropic. Some 25% of the latter harboured both poultry and T. infestans. Poultry were the only domestic animals associated with T. infestans, a finding that was exclusive to anthropic ecotopes. The proportion of feedings on individual fowl (61/146) was highly significant. Chicken coops are not used in Trinidad, and poultry brood in anthropic structures. Due to the materials used for making their nests and their repeated use, a periodic bug flow can be established from the intra- to the peridomiciliary area and vice versa, through passive transport. The close relationship among T, infestans, poultry, and humans in anthropic biotopes where other T. cruzi reservoirs such as dogs are also present contributes to the maintenance of domestic triatomine colonies and transmission of Chagas' disease to humans.

RESUMEN

Flight activity and invasion of houses by Triatoma sordida and T. guasayana were studied in the Province of Santiago del Estero, Argentina. Spontaneous findings of both species in houses were recorded from 1982 to 1989. Light trap collections were performed in 1982, 1983 and 1984, at the woods surrounding the settlements of Amamá (43 houses) and Trinidad (19 houses). Most of the 101 triatomines collected, were unfed and negative for Trypanosoma cruzi. T. guasayana predominated over T. sordida, and both appeared on the lighted screens between 19-31 min (mean 24) after dusk and the catch time was 30-45 min. Although entomological evaluation of 41 houses at Amamá performed in September 1985, just before insecticidal spraying, showed that Triatoma infestans predominated, adults of T. guasayana were collected in sleeping places, in 7 houses (17%). Most triatomines invading houses from then up to 1990 were flying T. guasayana (20/27) and females outnumbered males. Three non-infected T. guasayana females were fed on man and two T. guasayana males positive for "T. cruzi like" trypanosomes were unfed. Therefore, visiting hungry adults could transmit T. cruzi to people and introduce wild parasites to the domestic cycle. T. guasayana stands as the main potential substitute of T. infestans in the studied area, and it might play there the same role as T. sordida in Brazil.

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Trypanosoma cruzi infection in sylvatic mammals of the quebracho woods of the eastern part of Santiago del Estero province, Argentina, was studied from October 1984 to December 1987. 301 mammals of 20 different species were caught. T. cruzi, characterized biologically and biochemically, was isolated by xenodiagnosis from 23 of 72 (32%) Didelphis albiventris opposums, 2/36 (5.5%) Conepatus chinga skunks, and one ferret (Galictis cuja). 53 opossum refuges were located and triatomine bugs were found in 2 of them: one male Triatoma infestans, infected with T. cruzi, and 5 uninfected nymphs of T. sordida, had all fed on opossum blood. Electrophoretic zymogram patterns of the T. cruzi populations isolated from opossums and skunks were similar to isoenzyme profiles already described for populations isolated from infected humans in Argentina. The small number of triatomines found in the opossum refuges seems inadequate to account for the prevalence of T. cruzi infection recorded for these mammals, so other possible contaminative routes of infection should be investigated.

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We report the first systematic epidemiological research carried out in Argentina on the skunk Conepatus chinga. Forty-nine animals were captured in the settlements of Amamá, Trinidad, and nearby forested areas located in the Department of Moreno, Province of Santiago del Estero, between April 1985 and May 1989. Isolation of parasites was done through xenodiagnosis, and their identification as Trypanosoma cruzi was achieved by biological and biochemical criteria. The isolate was highly virulent and pathogenic in inoculated C3H mice. Prevalence was 4.1% (2 of 49). Two facts account for a possible domestic source of infection: both infected skunks were captured near Trinidad, in an area that had never been treated with insecticides, and electrophoretic isoenzyme patterns of the parasites isolated from the skunks were identical to those found in humans. Because extensive deforestation probably would increase the distribution area of C. chinga, further investigation should be performed to evaluate the epidemiological role of this wild mammal.

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