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Biomedical subjects

C J Schofield

Publications and source records attributed to C J Schofield.

At least 127 records · Page 7Linked to original sources
PubMed1985

Theoretical approach to active dispersal and colonization of houses by Triatoma infestans.

Dispersive flight by Triatoma infestans was modelled by assuming either unidirectional flight in a straight line, or that flight followed a pattern of 'random walk' analogous to two-dimensional Brownian motion. Parameter estimates for the models were derived from previous fieldwork in Argentina and Brazil. Calculated probabilities of houses becoming infested over a 1 year period were compared with actual changes of house infestation in a small farming community in central Brazil. It was found that infestation could be explained partly by the dispersive flight of the bugs according to the distances between houses, and partly by the predisposition of houses to infestation by virtue of their construction, since houses with cracked mud walls were particularly susceptible to infestation. Infested houses lying more than 200 m from uninfested houses appeared to make an almost negligible contribution to infestation of the uninfested houses. This suggests that buffer zones of this size around treated areas could help to minimize the risk of reinfestation after treatment.

Animals↗
PubMed1984

Isozyme heterogeneity and numerical taxonomy of Trypanosoma cruzi stocks from Chile.

Fifty-three stocks of Trypanosoma cruzi were isolated in Chile, 13 from patients, 32 from the domestic triatomine vector Triatoma infestans, and 8 from the silvatic and peridomestic vector T. spinolai. The majority of isolates from triatomine bugs were made by the direct culture of infected faeces. The 53 stocks and a single clone were characterized by a combination of starch-gel and cellulose acetate enzyme electrophoresis. Three groups of T. cruzi stocks were apparent from either simple visual comparisons of isozyme profiles or numerical taxonomy. The groups were designated Chilean zymodeme (Z) 1, which was similar to Brazilian Z1, Chilean Z2a, similar to Brazilian Z2 and Chilean Z2b, similar to Bolivian Z2 and with prominent heterozygous isozyme profiles. Chilean Z1 was isolated only from T. spinolai colonizing farm walls inhabited by the rodent Octodon degus. Chilean Z2a and Z2b were both isolated from domestic T. infestans T. infestans and man, in some cases within the same household. Hardy-Weinberg equilibria were not found amongst a group of 22 stocks from a single locality and deviations from theoretical Hardy-Weinberg distributions were compatible with the absence of genetic exchange in the sampled population of T. cruzi.

Alanine Transaminase↗
PubMed1982

The ecology of Chagas disease in Chile.

Chagas disease probably affects over half a million people in Chile, principally in rural communities in the fertile valleys of the arid 'norte chico' region, north of Santiago. The main domestic vector is Triatoma infestans, but Triatoma spinolai, although mainly in rocky sylvatic and peridomestic ecotopes, also invades houses. Since the Spanish invasion in the sixteenth century, and particularly during the last 100 years, the endemic region has suffered an ecological breakdown, largely due to excessive timbering and over-grazing, which has led to a denuded landscape with severe loss of agricultural productivity. This breakdown, combined with uneconomically sized farms and poor marketing, exacerbates the poverty of the rural communities. As in other similar areas of Latin America, the combination of poverty and poor education discourages improvements in housing which would reduce the risk of vector-transmitted Chagas disease. This paper reviews the historical and ecological background of the endemic region of Chile, both as a basis for further work, and as a point of comparison with other endemic areas. The review attempts to show how the current status of Chagas disease is likely to be maintained through its association with poor quality housing, poverty and ecological degradation, drawing parallels with other endemic++ areas and suggesting ways by which the ecological damage might be reversed.

Agriculture↗
PubMed1981

Field experiments of dispersive flight by Triatoma infestans.

Using marked male Triatoma infestans allowed to escape and fly on a little-used airport in Brazil and salt flats in Argentina, 33 of 169 flew in the former and 28 of 528 in the latter experiment. Many of the bugs which flew had been classed as poorly fed. The proportion of bugs which flew was in reasonable agreement with predictions based on laboratory observations. It was shown that in the field male bugs are capable of flights in excess of 100 m. The method described served the purpose of this experiment well but would not be suitable for distances greater than 100 to 200m.

Animals↗
PubMed1980

Density regulation of domestic populations of Triatoma infestans in Brazil.

Twenty old houses in a rural area of central Brazil were sampled monthly for Triatoma infestans during 16 months. The samples indicated peak adult emergence between January and May, preceded by peak emergence of stage V, IV and III nymphs respectively. Stage I and II nymphs were rarely taken in the samples. A much smaller peak of adult emergence occurred in September; thus the two peaks of adult emergence during the year were consistent with the approximately six months duration of egg-to-adult development usually recorded in laboratory studies. During January, 1977, when the study began, all houses were searched for dead bugs, exuviae, eggs and eggshells. These samples were used to calculate stage mortalities, from which a simple life-table was constructed. These data were combined with laboratory data concerning stage development times and female longevity and fecundity. Sensitivity analysis of the life-table showed it to be most sensitive to small changes in daily mortality rate and total egg-to-adult development time. The data were used to advance an hypothesis that the size of domestic populations of T. infestans is mainly controlled by changes in the egg-to-adult development time and, to a lesser extent, by changes in female reproductivity. Both these factors are in turn controlled by the nutritional status of the bug population, which, if the supply of food, i.e. number of hosts, is constant, is dependent upon the density of the bug population. It is argued that this mechanism of density regulation functions within limits set by the prevailing ambient temperature.

Animals↗
PubMed1978

A comparison of sampling techniques for domestic populations of Triatominae.

Six methods of sampling domestic populations of Triatoma infestans (Klug in Brazil have been studied. The results suggest that where bug densities are low, the Gomez-Nuñez box may be used, but with higher bug densities withdrawal or removal collecting allows a direct estimation of the size of the bug population. The number of samples to be taken in removal collections depends upon the density of the bug population and the degree of accuracy required.

Humans↗
PubMedDate not supplied

Dispersive flight by Triatoma sordida.

One hundred and thirty-two male and female Triatoma sordida were marked with fluorescent paint and released at an experimental site on the salt flats of central Argentina, distant from any inhabited dwellings. Flight by these bugs commenced just after sunset, and the bugs were then systematically searched for using portable ultraviolet lights. There was no apparent tendency for the bugs to fly in any particular direction, but those whose flight could be observed directly all seemed to fly in approximately straight lines at a height of 0.5-1 m. Of the 86 bugs that flew from the release point, 16 made trivial flights of less than 5 m, 4 landed at distances of 60-90 m away, while the other bugs were not recovered and appear to have flown further than 100 m. As expected from similar studies with T. infestans, the proportion of bugs initiating flight declined with increasing weight-length ratio, but T. sordida showed a much higher propensity for flight under these conditions than did T. infestans.

Animals↗