Trends in Parasitology
ReviewPotential effects of global environmental changes on cryptosporidiosis and giardiasis transmission
Section snippets
Environmental change and zoonotic diseases
Climate variability and large scale changes in land-use patterns have been implicated in the rising incidence of zoonotic parasitic diseases in humans (Table 1) [1]. Climate can directly affect pathogen survival and affect spread through water, food, and the environment (Table 2) 2, 3. Land-use patterns can influence pathogen load by altering the distribution of infective and vulnerable hosts, and can modify transmission pathways (Table 1) [4]. Global environmental changes could become a
Climate
Table 1 summarizes published studies that have examined the influence of climate variability and agricultural land use patterns on cryptosporidiosis and giardiasis incidence. Generally, a positive association between environmental temperatures and cryptosporidiosis in tropical and temperate regions has been reported. A pronounced and consistent seasonality in incidence has also been observed in the UK, US [14], and New Zealand [15]. However, a spatial analysis of temperature and
Agricultural land use
Positive associations of disease incidence with livestock density in New Zealand [34], the US [35] and Scotland [36], and higher infection rates in rural areas in Canada [36], suggest that livestock are a major source and reservoir for human cryptosporidiosis and giardiasis (Table 1) (Box 1). Moreover, in Scotland, human C. hominis (human strain) cases were associated with higher population density, whereas high ruminant density and rural living were associated with increased risk for C. parvum
Social and demographic determinants
Cryptosporidiosis and giardiasis are common enteric infections in poor countries [55]. Here, we concentrate on factors that are most likely to explain health disparities between high- and low-income nations: socioeconomic factors, infrastructure, and cultural practices. We also discuss the role of individual characteristics such as genetics, age, gender, and the presence of other chronic diseases.
Future research needs
This review has highlighted some important knowledge gaps that need to be addressed. First, our understanding of the linkages between environmental and social factors and disease incidence are largely driven by research conducted in developed countries. The nature and magnitude of environmental change will be different in high- and low-income settings, and adaptation strategies adopted from wealthy nations may not be applicable. Second, although industrialized countries have relatively rich
Concluding remarks
We have emphasized the significant influence of climate and land-use patterns on cryptosporidiosis and giardiasis incidence (Table 1). Specifically, the role of expected increases in temperature and variability in rainfall patterns and increasing agricultural land use, particularly livestock density, on disease risk is reviewed (Table 2). Importantly, although these factors can have independent effects, their effect on disease incidence is strongly influenced by social and demographic factors.
Acknowledgments
This work was supported by a University of Otago Postgraduate Scholarship.
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