A host immune hormone modifies parasite species interactions and epidemics: insights from a field manipulation.

Parasite epidemics can depend on priority effects, and parasite priority effects can result from the host immune response to prior infection. Yet we lack experimental evidence that such immune-mediated priority effects influence epidemics. To address this research gap, we manipulated key host immune hormones, then measured the consequences for within-host parasite interactions, and ultimately parasite epidemics in the field. Specifically, we applied plant immune-signalling hormones to sentinel plants, embedded into a wild host population, and tracked foliar infections caused by two common fungal parasites. Within-host individuals, priority effects were altered by the immune-signalling hormone, salicylic acid (SA). Scaling up from within-host interactions, hosts treated with SA experienced a lower prevalence of a less aggressive parasite, increased burden of infection by a more aggressive parasite, and experienced fewer co-infections. Together, these results indicate that by altering within-host priority effects, host immune hormones can drive parasite epidemics. This study therefore experimentally links host immune hormones to within-host priority effects and parasite epidemics, advancing a more mechanistic understanding of how interactions among parasites alter their epidemics.

Development of new sensitizations in asthmatic children monosensitized to house dust mite by specific immunotherapy.

It has been hypothesized that specific immunotherapy (SIT) significantly decreases the development of new allergen sensitizations in mono-sensitized patients. In this study, we evaluated the effect of SIT on the development of new allergen sensitizations in 129 asthmatic children mono-sensitized to house dust mite. SIT was accepted by only 70 of them (SIT group). The remaining 59 children were treated only with medication (control group). At the end of the study we found that 33% of all patients developed new sensitizations. Surprisingly, the prevalence of new sensitizations was significantly higher in the SIT group (45.5%) than in the control group (18.1 %). Ash tree (Fraxinus excelsior), Olive and Meadow fescue (Festuca elatior) were the most common allergens responsible for the new sensitizations. We conclude that SIT did not prevent the onset of new sensitizations in asthmatic children mono-sensitized to house dust mite.