Host resistance and parasite virulence in greenfinch coccidiosis

Abstract

The question why different host individuals within a population differ with respect to infection resistance is of fundamental importance for understanding the mechanisms of parasite‐mediated selection. We addressed this question by infecting wild‐caught captive male greenfinches with intestinal coccidian parasites originating either from single or multiple hosts. Birds with naturally low pre‐experimental infection retained their low infection status also after reinfection with multiple strains, indicating that natural infection intensities confer information about the phenotypic ability of individuals to resist novel strains. Exposure to novel strains did not result in protective immunity against the subsequent infection with the same strains. Infection with multiple strains resulted in greater virulence than single‐strain infection, indicating that parasites originating from different host individuals are genetically diverse. Our experiment thus demonstrates the validity of important but rarely tested assumptions of many models of parasite‐mediated selection in a wild bird species and its common parasite.

Simple and noninvasive method for assessment of digestive efficiency: Validation of fecal steatocrit in greenfinch coccidiosis model

“…This finding implies that steatocrit enables to identify much more subtle effects on digestion than measurement of oocyst shedding or circulating fats. It also confirms the previous finding in the same model system that new, heterologous parasite strains appear more virulent than familiar strains (Hõrak et al., 2006). …”

“…We thus predicted that (i) treatments with toltrazuril and sulfadimethoxine result in decrease in steatocrit values as compared to untreated control birds. We have also shown that infecting greenfinches with novel coccidian strains originating from multiple hosts cause decline in body mass and plasma triglyceride levels (Hõrak, Saks, Karu, & Ots, 2006). Hence, we predicted that (ii) such experimental infection will result in increase in steatocrit as compared to untreated control birds.…”

Antioxidant protection, carotenoids and the costs of immune challenge in greenfinches

“…The coccidian species present in the feces of migrating greenfinches in Estonia has been previously identified as Isospora lacazei (for details, see Hõrak et al, 2004). Coccidian-infection intensities (number of oocysts per gram of feces) of individual greenfinches were quantified as described previously (Hõrak et al, 2004;Hõrak et al, 2006;Saks et al, 2006). Infection intensities were determined on days 4, 6, 8, 10, 12, 16, 18, 20-22, 24-34, 36, 37, 39, 41, 44, 47 and 48 of the experiment.…”

Immunity and Virulence in Bird-Parasite Interactions

“…This approach has been mostly adopted for hosts with asexual reproduction where clones can be easily infected with different parasite strains [47]. One of the rare studies, dealing with a bird species, addressing the importance of genetic variation among hosts and parasite strains for the outcome of the interaction has been recently published by Hõrak et al [48]. They experimentally infected greenfinches (Carduelis chloris) with single and multiple coccidian strains (Isospora lacazei).…”