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Sonographic evidence of asymptomatic Echinococcus granulosus lesions in the liver was found in 156 of 9,515 persons in the Department of Florida, Uruguay. The sensitivity of ELISA and latex agglutination serology compared with ultrasound was 47.6% and 28.1%, respectively, and specificity was Ͼ 85%. There was a significant positive association between positive sonography and a personal history of previous but treated Echinococcus infection while those that were seropositive but ultrasound-negative were significantly more likely to have a personal history of infection or a history of infection in their family. Prevalence of infection increased significantly with age. There was no correlation between echinococcosis and dog ownership or home slaughter of sheep but offal disposal was important, with an increased prevalence of infection of 3.2%, 2.8%, and 3.1%, respectively, in persons feeding offal to dogs or burying or burning it compared with a prevalence of 0.8-1.5% in those using other methods of disposal. Almost half the population, when questioned, seemed to have sound knowledge about E. granulosus and described correct treatment of E. granulosus in dogs but this did not affect prevalence. There was a significant positive association between infection and the presence of a fenced fruit/vegetable garden and use of rural waters, particularly the cachimba (a small dam) and the aljibe (a cistern or tank) that collect rainwater from the ground surface and roofs, respectively.

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Unveiling the mechanisms that molds populations fluctuations is central for understanding the dynamic of pest outbreaks, harmful algal blooms, or extinction risk. We hypothesize that metabolic restriction to maximum population abundance shapes single population and community fluctuations. Here, we derive a formal theoretical model linking metabolic limits to maximum population abundance with the distribution of fluctuations of single populations and communities. First, we show that the emergence of fat tails in the distribution of single population fluctuations is caused by the metabolic effect on maximum population abundance of periodic changes in resource supply or temperature. Second, we show an explicit link between single population fluctuations and the Laplace distribution of aggregated community fluctuations. Third, we derive a general relationship between population variance and body mass (called variance-mass allometry; VMA). This framework provides a theoretical mechanism to explain fat-tailed distributions of population fluctuations. It also predicts a double exponential or Laplace distribution of community fluctuations when the range of body size in the community is large. Finally, it provides a generalization of the VMA model which is able to generate theoretical predictions about patterns of variability among species lifestyles. This framework provides specific theoretical predictions that can be benchmarked against alternative competing models and empirical data, hence furthering our understanding about how metabolism determines abundance fluctuations.