The evolution of Chagas' cardiomyopathy is poorly understood. We therefore examined the development of cardiac lesions in a rural Brazilian community for a period of 7 years. Initially, 42% of 1017 residents were seropositive for infection with Trypanosoma cruzi. Age-specific infection rates indicated that most had become infected before the age of 20 years. On follow-up, it appeared that those persons who developed cardiac lesions did so soon after infection, since the incidence of right bundle branch block and other ventricular conduction defects (VCDs) was also highest before age 20 years. The progressive nature of these lesions was demonstrated by frequent development of additional electrocardiographic abnormalities and high mortality among infected adults with VCDs. In contrast, mortality was low and approximately the same for seropositive and seronegative adults under 60 years who had normal electrocardiograms. Electrocardiography during the early asymptomatic stage of infection was able to distinguish persons with potentially lethal cardiac lesions from those with a benign prognosis.

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To assess the effect of removing leishmania-infected dogs on the incidence of visceral leishmaniasis, a controlled intervention study was performed in northeast Brazil. The attempted elimination of seropositive dogs resulted in an initial significant decrease in the annual incidence of seroconversion among dogs from 36% to 6% over the first two years. In the following two years, the incidence increased to 11% and 14%, respectively. In a control area in which dogs were surveyed but seropositive dogs were not removed, the cumulative incidence did not vary significantly from year to year, ranging from 16% to 27%. In the intervention area, the prevalence of dog seropositivity decreased from 36% before the intervention to 10% and remained stable. These findings suggest that attempting to remove seropositive dogs is insufficient as a measure for eradicating visceral leishmaniasis in dogs. However, the force of transmission of infection among dogs can be reduced by such programs. Also, when the number of human cases before and after the start of the intervention was calculated, a significant decrease in incidence of disease in the intervention area was observed among children less than 15 years of age (P Ͻ 0.01). The results of this intervention study suggest that the elimination of the majority of seropositive dogs may affect the cumulative incidence of seroconversion in dogs temporarily and may also diminish the incidence of human cases of visceral leishmaniasis.

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In this study, we compare the development of infection and/or disease in Beagle dogs intradermally infected with Leishmania chagasi, in the presence or absence of Lutzomyia longipalpis saliva, with those of intravenously infected animals. Spleen samples of all the animals inoculated with parasites had positive polymerase chain reaction tests for Leishmania DNA. Positive spleen cultures for Leishmania were detected earlier (P < or = 0.018) and were more frequent (five out of the five animals) in intravenously infected animals than in the intradermally infected animals, in presence (two out of the six animals) or absence (three out of the five animals) of salivary gland lysate of L. longipalpis. Significant increase in serum antibodies against Leishmania was observed only in the intravenously infected group (P = 0.004). In addition, dogs with infection confirmed by isolation of amastigotes or detection of parasite DNA were, nevertheless, negative for anti-Leishmania antibodies up to 5 months or more after infection. Only animals of the intravenously infected group developed progressive decreases in hematocrit (Pearson r = -0.8076, P = -0.0026) and hemoglobin (Pearson r = -0.8403, P = 0.0012) during the infection period. No significant difference in the course of infection was observed between groups of intradermally infected animals. The data presented herein confirms that the intradermal inoculation of dogs with Leishmania produces an asymptomatic form of infection. It also fails to show an advantage in using L. longipalpis saliva as an infection-enhancing agent in experimental canine leishmaniasis.

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An opossum, Didelphis albiventris, from Jacobina, Bahia State, was found naturally infected with Leishmania donovani, being the first non-canid wild mammal to be detected with the agent of kala-azar in the New World.