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Cryptosporidium and Giardia-zoonoses: fact or fiction?
1Australian Water Quality Centre, South Australian Water Corporation and Cooperative Research Centre for Water Quality and Treatment, Private Mail Bag 3, SA 5108, Salisbury, Australia. paul.monis@sawater.com.au
Abstract:
Giardia and Cryptosporidium are enteric protozoan parasites that infect a wide range of vertebrate hosts. Both are transmitted either by direct faecal/oral contact or by the ingestion of contaminated food or water. The discovery of morphologically similar organisms infecting humans and a variety of mammals and birds has led to the proposal that both Cryptosporidium and Giardia are zoonotic (i.e. transmitted in nature between humans and animals). Transmission between humans and animals has been supported by cross-infection studies. However, closer examination of many of these studies reveals limitations in the methodologies utilised. More recent molecular genetic studies have demonstrated considerable genetic diversity among isolates of the same species of Giardia and Cryptosporidium, suggesting that these species are in fact species complexes and that some of these novel species may be host-specific. This paper will critically examine the evidence for the zoonotic transmission of these parasites.
Insights
Giardia and Cryptosporidium are zoonotic parasites, but molecular studies reveal significant genetic diversity, suggesting some species may be host-specific, challenging previous assumptions of widespread zoonotic transmission.
Area of Science:
- Veterinary Parasitology
- Zoonotic Diseases
- Molecular Epidemiology
Background:
- Giardia and Cryptosporidium are common enteric protozoan parasites with a broad host range.
- Zoonotic transmission between animals and humans has been proposed due to morphological similarities and cross-infection studies.
- Previous studies on zoonotic potential have methodological limitations.
Purpose of the Study:
- To critically evaluate the evidence supporting the zoonotic transmission of Giardia and Cryptosporidium.
- To investigate the impact of molecular genetic data on understanding parasite transmission dynamics.
- To explore the host specificity of different Giardia and Cryptosporidium species complexes.
Main Methods:
- Review of existing cross-infection studies on Giardia and Cryptosporidium.
- Analysis of molecular genetic data from various host-specific isolates.
- Critical examination of methodologies used in zoonotic transmission research.
Main Results:
- Morphological similarities initially suggested widespread zoonotic potential.
- Cross-infection studies provided limited, methodologically flawed evidence for zoonotic transmission.
- Molecular genetic studies reveal significant diversity, identifying species complexes and potential host specificity.
Conclusions:
- The evidence for widespread zoonotic transmission of Giardia and Cryptosporidium is not robust.
- Genetic diversity suggests that some species or genotypes may be host-specific.
- Further molecular research is needed to accurately define transmission pathways and host ranges.