[Prevalence of Trypanosoma cruzi infection in opossum (Didelphis albiventris) in Santiago del Estero, Argentina]. / Estudio de la prevalencia de la infección por Trypanosoma cruzi en zarigüeyas (Didelphis albiventris) en Santiago del Estero, Argentina.

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.

Complex cytogenetic rearrangement in a case of unicameral bone cyst.

Cytogenetic analysis of a unicameral bone cyst surgically resected in an 11-year-old boy revealed a highly complex clonal structural rearrangement involving chromosomes 4, 6, 8, 16, 21, and both 12. These findings reinforce the need for further studies on unicameral bone cysts to verify the frequency and to understand the significance of chromosome anomalies in this type of lesion.

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 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.

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.

A new host of Trypanosoma cruzi from Jujuy, Argentina: Octodontomys gliroides (Gervais & D'Orbigny, 1844) (Rodentia, Octodontidae).

To identify wild hosts of Trypanosoma cruzi, surveys were conducted in the subandean valleys of Jujuy Province, Argentina, between June 1986 and March 1987. Seventy two mammals from 13 different species were examined by xenodiagnosis. Fifty two of them were mostly rodents trapped at the localities of Maimará, León and Tilcara, and the remainder had been kept in captivity at the Estación Biológica Experimental, in Jujuy. Trypanosoma cruzi infection was detected only in 2 Octodontomys gliroides (2 pos./8 exam. 25%) from all 72 examined mammals. Isolates were called Octodontomys Argentina 1 and 2 (OA1 and OA2). Both infected animals were caught at the archaelogical ruin of Pucará, at Tilcara. Repeated searches for triatomines in the ruin itself and in neighbour houses rendered negative results. Groups of mice inoculated with either OA1 or OA2 isolates became infected between 7 (OA1) to 12 days (OA2) postinoculation PI. Parasitemia peaks were observed between day 12th-14th PI. Scarce amastigote nests were found in myocardium and skeletal muscle. Mortality was observed only for mice inoculated with OA1. Isoenzyme patterns of OA1 and OA2 were identical to one found in dogs and slightly different from that of human parasites in Argentina. Bones from Octodontomys sp., were recently found in a cave, dated 10200-8600 BC, in Pumamarca, near Tilcara, Jujuy. There are evidences that O. gliroides cohabited with man in ancient times and was associated to the domestic cycle of T. cruzi transmission, playing a role like that of domestic caves in Bolivia.

Sylvatic American trypanosomiasis in Argentina. Trypanosoma cruzi infection in mammals from the Chaco forest in Santiago del Estero.

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.

The skunk Conepatus chinga as new host of Trypanosoma cruzi in Argentina.

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.