Escherichia coli heat-stable enterotoxin is a low-molecular-weight substance that has been shown to induce the active secretion of fluid and electrolytes in the small intestine. In this study, we have characterized the effects of purified E. coli heat-stable toxin (ST, strain 18D, serotype 042:K86:H37) on the motility of rabbit small intestine by using myoelectric recording techniques. Substances, such as cholera toxin, that activate the adenylate cyclase-cAMP system induced predominantly migrating action-potential complex activity. E. coli ST, a toxin that activates the guanylate cyclase-cGMP system, was infused into isolated in vivo ileal loops of New Zealand White rabbits. Inactivated toxin was also studied by exposing the ST to 1 mM dithiothreitol for 90 min. Active E. coli ST induced only repetitive bursts of action potentials. When the toxin was inactivated with dithiothreitol, no alteration in myoelectric activity was observed. We speculate that repetitive bursts of action-potential activity may represent a virulent factor of the bacterium, altering motor activity to slow transit and allowing for bacterial proliferation and invasion.

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In view of the lack of clinical and epidemiological data on human leptospirosis in the State of Mato Grosso do Sul, and the possibility of confounding it with other diseases, sera from patients with a preliminary clinical suspicion of dengue or viral hepatitis but without laboratory confirmation were examined by means of microscopic seroagglutination techniques for leptospirosis. The seroreactivity rates among the samples with clinically suspected dengue or viral hepatitis were 15.9% and 9%. The most frequent serovar was Hurstbridge (70.4%) and the serovar with the highest titer was Canicola (1:51,200). No association was found between seropositivity and the patients sex, age or occupation. This study demonstrated that, although the present notifications of leptospirosis cases in Mato Grosso do Sul are negligible, the prevalence of antibodies was high in the groups investigated. Therefore, the hypothesis that there is undernotification of human leptospirosis cases in this State and difficulties in the differential diagnosis between dengue and viral hepatitis should be considered.

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