<i>Giardia</i> - significance of zoonotic routes in human infections.
2015
Ballweber, L. R.
<i>Giardia</i> are flagellated protozoan parasites of numerous animals. Species of <i>Giardia</i> were originally described based, primarily, on the host from which they were isolated; later, isolates that were morphologically identical with <i>Giardia duodenalis</i> were synonymized with that species. Accumulating genetic evidence, however, indicates that <i>G. duodenalis</i> is a species complex in which members are morphologically identical, but, genetically distinct. At least eight distinct groups (=assemblages) have been identified, all of which likely constitute unique species. Although zoonotic transmission may occur in discrete circumstances, people to people transmission is likely much more important. However, the human disease burden associated with zoonotic transmission still needs to be assessed, including differences in the biology and clinical manifestations associated with the various types. Genetic targets for typing have been identified but do not work well for all assemblages, particularly assemblage B; thus, the search for appropriate targets must continue. Multilocus genotyping and standardized terminology is highly recommended as interpretations based on single markers may lead to incomplete conclusions. Combining appropriate genetic markers with well-designed epidemiological studies will be necessary to further our understanding of <i>Giardia</i> transmission patterns and infection sources for both people and animals.
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