Effects of anthropogenic land use change on the ecology of the chagas disease agent Trypanosoma cruzi
Gottdenker, Nicole Lynn
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Anthropogenic landscape change is associated with increased infectious disease transmission in terrestrial and aquatic ecosystems. Understanding pathogen responses to environmental disturbance is necessary to prevent and control disease emergence in wildlife, domestic animals and humans. The objective of this study is to evaluate how deforestation impacts transmission of the vector-borne parasite Trypanosoma cruzi, agent of Chagas disease in humans. T. cruzi cycles between triatomine bug vectors and wild mammals, domestic mammals, and humans, and is a significant cause of morbidity and mortality in Latin America. Recent studies suggest human encroachment on forest ecosystems causes increased risk of T. cruzi transmission to humans. Key hypotheses of this study are: 1) vector abundance increases in deforested habitats due to an increased contact with opportunistic wild mammals and domestic mammals 2)T. cruzi vector infection increases in deforested areas because of increased contact with competent disease reservoirs 3) T. cruzi vector infection is lower in intact forests because of higher species diversity and contact with highly competent disease reservoirs (a ’dilution’ effect). This study took place in protected forests and deforested landscapes surrounding the Panama Canal, Panama. The triatomine bug Rhodnius pal lescens, the principal vector of Chagas disease in Panama, was collected (N=1186) from its primary habitat, the palm Attalea butyraceae, in five different habitat types reflecting a gradient of anthropogenic disturbance. Collected R. pal lescens (N=641) were tested for infection with T. cruzi and a congeneric parasite T. rangeli by a duplex PCR (polymerase chain reaction) assay. In order to evaluate potential effects of species diversity and composition on vector infection with T. cruzi, vector blood meals were identified by PCR amplification of the vertebrate 12S rRNA gene. Results show that deforestation and forest fragmentation are associated with increased vector abundance and vector infection prevalence with Trypanosoma cruzi. Contrary to hypothesis 3, there was a positive association between blood meal species diversity and T. cruzi infection prevalence. On the other hand, blood meal species composition appears to be an important driver of T. cruzi transmission in the deforested landscape. These results suggest that anthropogenic land use change can drive increased R. pallescens abundance and T. cruzi vector infection prevalence.