Molecular epidemiology of Giardia and Cryptosporidium infections

- The molecular ecology of Giardia and Cryptosporidium is reviewed.
- What questions have molecular tools resolved?
- Taxonomic issues still predominate and are a hindrance to moving forward.
- Giardia is zoonotic but consensus required on which molecular 'tools' to use.
- Cryptosporidium is a gregarine and its biology and ecology should be reappraised.

Giardia and Cryptosporidium are ubiquitous enteric protozoan pathogens of vertebrates. Although recognised as the aetiological agents of disease in humans and domestic animals for many years, fundamental questions concerning their ecology have been unresolved. Molecular tools have helped to better understand their genetic diversity and in so doing have helped to resolve questions about their transmission patterns and associated impacts on public health. However, the value of molecular tools is often complicated by questions concerning their applications, interpretation of results and terminology. Taxonomic issues have, until recently, made it difficult to determine the epidemiology of infections with both Giardia and Cryptosporidium. Similarly, improved understanding of their respective phylogenetic relationships has helped to resolve questions about zoonotic potential and distribution in wildlife. In the case of Cryptosporidium, imaging technologies have complemented phylogenetic studies in demonstrating the parasite's affinities with gregarine protozoa and have further supported its extracellular developmental capability and potential role as an environmental pathogen.