Giardia spp

Hillman, Alison E., Ash, Amanda L., Lymbery, Alan J. & Thompson, R. C. Andrew, 2019, Anthropozoonotic significance, risk factors and spatial distribution of Giardia spp. infections in quenda (Isoodon obesulus) in the greater Perth region, Western Australia, International Journal for Parasitology: Parasites and Wildlife 9, pp. 42-48 : 46-47

4.2. Giardia spp . in quenda — risk factors for infection

An association between urban environments and Giardia spp . infection in quenda was previously identified by Hillman et al. (2017b). However, in exploring this association further regarding putative confounding, this association dissipated, pointing towards more specific causal mechanisms behind the association, such as differing host population density and/or synergistic parasite infection risk across these environments, which may have been controlled for by other covariates in the multivariable analyses (as discussed further below).

Concurrent Cryptosporidium spp. infection was associated with Giardia spp . infection risk. It is possible that this reflects similar transmission pathways to Giardia spp . infection, or is confounded by host population density. Additionally or alternatively, synergistic interactions may occur between these parasite taxa within the quenda host — for example, through immune-mediated collaboration ( Northover et al., 2018). It must be noted, that although Cryptosporidium spp. was the only gastrointestinal parasite that remained associated with Giardia spp . infection risk on multivariable analysis, associations between Giardia spp . and other gastrointestinal parasite taxa may not have been detected, due to a number of negative influences on the statistical power of this study to detect less marked associations. These include relatively small sample sizes (particularly for Entamoeba spp. infection), very high or low prevalences of some parasite taxa, and non-differential misclassification bias in the Potorolepis spp. infection analysis due to the utilised detection test lacking sensitivity in the detection of this parasite genus ( Hillman et al., 2017a).

The association between Giardia spp . infection and flea infection intensity is likely to be attributable to host population density: quenda in areas of higher population density may have an increased risk of infection with fleas and increased risk of higher flea infection intensity, as well as having an increased odds of Giardia spp . infection, compared to quenda in areas with lower population density. Quenda population density was not measured directly in undertaking the trapping of animals, due to constraints regarding the safety of captured animals, particularly in urban environments. However, controlling for other density-dependent parasites as part of these analyses may have partially controlled for host population density. Associations between flea infection intensity and host population density have been demonstrated in other mammalian host species (e.g. Krasnov et al., 2004; Kaal et al., 2006), as have associations between Giardia spp . infection and host population density (e.g. Atwill et al., 1997; Claerebout et al., 2009; Dreelin et al., 2014).