Current status of onchocerciasis in Colombia.

To assess the current epidemiologic status of onchocerciasis in Colombia two surveys were undertaken in 1995 in a suspected new focus on the border between Colombia and Ecuador and in the known focus located on the Micay River. No new focus was found along the Colombia-Ecuador border. In the known focus, communities along the upper Micay River and its tributaries were surveyed; 655 adults underwent physical examinations and skin biopsies. Infected individuals were found almost exclusively in the community of Naiciona, where prevalence of infection was 40% (36 of 91). Polymerase chain reaction detection of onchocercal DNA in skin snips correlated with the skin-snip biopsy results. The prevalence of punctate keratitis, the only ocular manifestation found, was 33%. A rapid entomologic assessment demonstrated Simulium exiguum infected with Onchocerca volvulus. This is the first finding in Colombia of naturally infected black flies and confirms S. exiguum as a vector species. These data will be used for implementing a control program using periodic ivermectin distribution.

In situ characterization of the human host response to Leishmania panamensis.

Both host and parasite determinants influence the outcome of Leishmania infections. Human host responses in cutaneous leishmaniasis of limited duration caused by a single species of the Viannia (V) subgenus were studied in skin biopsies obtained from lesions caused by Leishmania (V) panamensis in 31 male patients from the Colombian Pacific Coast. Dermal infiltrates and histopathologic changes were characterized using monoclonal antibodies and an indirect immunoperoxidase method. Dermal distribution of T-cell subpopulations and B-lymphocytes was nonrandom: CD4+ and CD8+ T cells were most frequent in the upper dermis, and B cells were most abundant in the lower dermis. Parasites, macrophages, and neutrophils were localized predominantly in the middermis. Multiple regression analyses to establish associations between lesion type (ulcer, nodule, or papule), immune response data (Montenegro skin test, indirect fluorescence antibody test titers, lymphocyte blastogenesis), and particular cell populations demonstrated statistically significant correlations between CD4+ lymphocytes and macrophages (p < 0.05). CD8+ lymphocytes were associated with plasma cells (p < 0.001), as was the presence of amastigotes (p < 0.05). These associations and the in situ divergence of CD4 and CD8 ratios suggest that prognostic indicators for disease evolution could be identified by prospective analysis of cellular relationships and response to therapy.

Infectivity of Trypanosoma rangeli in a promonocytic mammalian cell line.

The existence of an intracellular stage of Trypanosoma rangeli in the vertebrate host was evaluated by experimental infection of the U937 histiocytic cell line with the San Agustín strain and the Ub66-5b clone. The identity of the parasites at the beginning and end of the experiments was confirmed through biological behavior in the vector and mammal hosts, isoenzymes, polymerase chain reaction (PCR), and monoclonal antibodies. Infectivity to U937 cells of T. rangeli obtained from culture and salivary glands was evaluated under different experimental conditions. These included 34 C vs. 37 C, opsonized vs. nonopsonized parasites, and 2, 4, 6, 24, 48, and 72 hr of cell-parasite contact. Trypanosoma rangeli adopted a characteristic nondividing amastigote-like form within U937 cells, which was different in size (P = 0.001) from Trypanosoma cruzi amastigotes. Culture forms of T. rangeli were more infective than parasites from salivary glands (P = 0.049) but were less infective than T. cruzi (P = 0.0001). Variations in temperature (34-37 C) and complement opsonization did not affect infectivity. Viability of intracellular forms was confirmed by feeding Rhodnius prolixus with T. rangeli-infected cells. Resistance of T. rangeli to the intracellular milieu could be an important mechanism in producing chronic infections in mammals and in the infection of triatomines.