The kinetoplastid Protozoa are responsible for devastating diseases. In the Americas, Trypanosoma cruzi is the agent of Chagas' disease--a widespread disease transmissible from animals to humans (zoonosis)--which is transmitted by exposure to infected faeces of blood-sucking triatomine bugs. The presence of genetic exchange in T. cruzi and in Leishmania is much debated. Here, by producing hybrid clones, we show that T. cruzi has an extant capacity for genetic exchange. The mechanism is unusual and distinct from that proposed for the African trypanosome, Trypanosoma brucei. Two biological clones of T. cruzi were transfected to carry different drug-resistance markers, and were passaged together through the entire life cycle. Six double-drug-resistant progeny clones, recovered from the mammalian stage of the life cycle, show fusion of parental genotypes, loss of alleles, homologous recombination, and uniparental inheritance of kinetoplast maxicircle DNA. There are strong genetic parallels between these experimental hybrids and the genotypes among natural isolates of T. cruzi. In this instance, aneuploidy through nuclear hybridization results in recombination across far greater genetic distances than mendelian genetic exchange. This mechanism also parallels genome duplication.

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This paper describes an attempt to explore how far a categorisation of citations could be used as part of an assessment of the outcomes from health research. A large-scale project to assess the outcomes from basic, or early clinical, research is being planned, but before proceeding with such a project it was thought important to test and refine the developing methods in a preliminary study.Here we describe the development, and initial application, of one element of the planned methods: an approach to categorising citations with the aim of tracing the impact made by a body of research through several generations of papers. The results from this study contribute to methodological development for the large-scale project by indicating that: only for a small minority of citing papers is the cited paper of considerable importance; the number of times a paper is cited can not be used to indicate the importance of that paper to the articles that cite it; and self-citations could play an important role in facilitating the eventual outcomes achieved from a body of research.

Eleven of 27 decameric primers were found to be suitable for random amplification of polymorphic DNA (RAPD) from triatomine bugs on the basis that they produced discrete profiles and distinguished among Panstrongylus megistus (Burmeister), Rhodnius prolixus Stål, and Triatoma infestans (Klug). The legs, or single leg segments, of individual bugs were used as the source of DNA so that the taxonomic value of the bug was conserved. Within the scope of the specimens studied, RAPD profiles allowed assignment to species even when bugs were kept dry for up to 12 mo. Profiles for individuals within a species were not identical. RAPD profiles, with the specimens tested, distinguished among species of 3 pairs considered to be morphologically similar and closely related, namely, Rhodnius ecuadorensis Lent & León and Rhodnius pictipes Stål; Rhodnius nasutus Stål, and Rhodnius neglectus Lent; Rhodnius prolixus Stål and Rhodnius robustus Larrousse. RAPD data conformed with the perceived affinities among these species. RAPD polymorphisms were seen with T. infestans from 3 different localities, but none of the polymorphisms was confined to 1 source. RAPD provided a molecular basis to reassess taxonomic relationships within the Triatomine subfamily. The accurate distinction of triatomine species and of intraspecific bug populations may contribute to elimination of vector-borne Chagas disease from the Americas.

SUMMARYFactors which affect adhesion of cultured Trypanosoma congolense bloodstream forms to mammalian feeder cells have been examined. Using an in vitro binding assay, the initial events following interaction of trypanosomes with bovine aorta endothelial (BAE) cells were monitored by both light-and electron microscopy. Metabolic inhibitors and other biochemicals were incubated with either cells or parasites, to test whether any inhibited the process. Our findings suggest that adhesion of the parasites is an active process requiring metabolic energy from the trypanosomes, but not from endothelial cells. We also provide data suggesting that T. congolense bloodstream forms possess a lectin-like domain, localized at distinct sites on their flagellar surface, which interacts with specific carbohydrate receptors, most likely sialic acid residues, on the endothelial cell plasma membrane. We also suggest that the cytoskeletal protein actin is probably involved in this interaction.

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Understanding the impact of research requires multiple approaches. With refinement, these techniques could be employed more widely and potentially could inform research policy.

A Leishmania donovani-complex specific DNA probe was used to confirm the widespread dissemination of amastigotes in apparently normal skin of dogs with canine visceral leishmaniasis. When Lutzomyia longipalpis were fed on abnormal skin of five naturally infected dogs 57 of 163 (35%) flies became infected: four of 65 flies (6%) became infected when fed on apparently normal skin. The bite of a single sandfly that had fed seven days previously on a naturally infected dog transmitted the infection to a young dog from a non-endemic area. Within 22 days a lesion had developed at the site of the infective bite (inner ear): 98 days after infection organisms had not disseminated throughout the skin, bone marrow, spleen or liver and the animal was still serologically negative by indirect immunofluorescence and dot-enzyme-linked immunosorbent assay. When fed Lu. longipalpis were captured from a kennel with a sick dog known to be infected, 33 out of 49 (67%) of flies contained promastigotes. In contrast only two infections were detected among more than 200 sandflies captured in houses. These observations confirm the ease of transmissibility of L. chagasi from dog to sandfly to dog in Teresina. It is likely that canine VL is the major source of human VL by the transmission route dog-sandfly-human. The Lmet2 DNA probe was a useful epidemiological tool for detecting L. chagasi in sandflies.