GIARDIA AND CRYPTOSPORIDIUM From Molecules to Disease
Introduction
The protozoa that collectively comprise the genus Giardia have intrigued biologists
and clinicians for over 300 years, ever since Antony van Leeuwenhoek fi rst
discovered the organism (Meyer, 1994). This enigmatic protozoan possesses a
number of unusual characteristics including the presence of two similar, transcriptionally
active diploid nuclei, the absence of mitochondria and peroxisomes, and
a unique attachment organelle – the ventral sucking disc (Thompson and Monis,
2004; Morrison et al., 2007). Phylogenetic relationships are controversial, with
one school of thought suggesting that Giardia is a basal eukaryote and the other
that Giardia comprises one of many divergent eukaryotic lineages that adapted to
a microaerophilic lifestyle rather than diverging before the endosymbiosis of the
mitochondrial ancestor (Thompson and Monis, 2004; Morrison et al., 2007).
Despite its long history, our understanding of the pathogenesis of Giardia
infections and its relationship with its host is limited, and we do not know why
clinical disease occurs in some individuals but may not be apparent in others
Introduction
The protozoa that collectively comprise the genus Giardia have intrigued biologists
and clinicians for over 300 years, ever since Antony van Leeuwenhoek fi rst
discovered the organism (Meyer, 1994). This enigmatic protozoan possesses a
number of unusual characteristics including the presence of two similar, transcriptionally
active diploid nuclei, the absence of mitochondria and peroxisomes, and
a unique attachment organelle – the ventral sucking disc (Thompson and Monis,
2004; Morrison et al., 2007). Phylogenetic relationships are controversial, with
one school of thought suggesting that Giardia is a basal eukaryote and the other
that Giardia comprises one of many divergent eukaryotic lineages that adapted to
a microaerophilic lifestyle rather than diverging before the endosymbiosis of the
mitochondrial ancestor (Thompson and Monis, 2004; Morrison et al., 2007).
Despite its long history, our understanding of the pathogenesis of Giardia
infections and its relationship with its host is limited, and we do not know why
clinical disease occurs in some individuals but may not be apparent in others
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