Invited reviewRecent insights into the mucosal reactions associated with Giardia lamblia infections
Section snippets
Giardia lamblia and giardiasis
Giardia lamblia (syn. Giardia duodenalis, Giardia intestinalis) is a common intestinal dwelling protozoan and causes diarrhoea in humans and animals worldwide. One of the major sources of infection in humans is contaminated water but there is also strong evidence that the parasite is transmitted by person-to-person contact or by contact with domestic and wild animals (e.g. reviewed by Adam, 1991; Thompson, 2000).
The life cycle of G. lamblia includes two major stages: the proliferative
Immunological host reactions against G. lamblia infections
In the past decade, the immune response against G. lamblia has been especially investigated in terms of the parasite's ability to continuously change its surface antigen coat (e.g. reviewed by Müller and Gottstein, 1998; Nash, 2002). These studies have revealed that antigenic variation is associated with a unique family of surface antigens, named VSP (variant surface protein). Surface antigen alterations are observed within proliferating populations of intestinal trophozoites (Gottstein et al.,
Physiological host reaction against G. lamblia infections
While the immunological processes of the antigiardial host response has already been intensely investigated, little is known about non-immune defences. For example, intestinal Paneth cell-derived defensins (Ouellette, 1999), also known as cryptdins, have been proven to display a cytotoxic effect on G. lamblia in vitro (Aley et al., 1994) but no conclusive data are available regarding the physiological significance of these antimicrobial peptides in vivo. G. lamblia seems not to be able to
Intestinal pathogenesis associated with G. lamblia infections
As outlined above, the most important clinical signs of giardiasis are diarrhoea and malabsorption. Although various intestinal abnormalities have been described (Table 2), the pathophysiology associated with these symptoms is still incompletely understood (e.g. reviewed by Farthing, 1996, 1997; Eckmann and Gillin, 2001). In giardiasis, intestinal colonisation by the parasite seems to cause microvillus shortening (Erlandsen and Chase, 1974; Scott et al., 2000, 2004), villous flattening or
Concluding remarks
Although scientists in the field of giardiasis have already investigated multiple aspects of the immunological and physiological interplay between G. lamblia and its host intestinal environment the particular processes that determine the outcome of the parasite infection are still incompletely understood. In the past, most of the relevant data were generated either in vitro by co-cultivation of G. lamblia with different intestinal epithelial cell lines or in vivo by analysing G. lamblia
Acknowledgements
We thank Andrew Hemphill for careful reading of the manuscript. Supported by a grant obtained from the Swiss National Science Foundation (No. 31-066795.01).
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