Meeting Abstract
In many host-pathogen systems, there is significant individual variation in the frequency and dose of pathogen exposure. Heterogeneity in exposure may result in differences in disease progression, the formation of immunological memory, and subsequent protection from future pathogen exposures. In the naturally-occurring house finch-Mycoplasma gallisepticum (MG) system, the pathogen is transmitted via bird feeders, and thus birds are likely exposed to frequent low doses of pathogen while foraging. We aimed to experimentally mimic heterogeneous exposure during foraging in order to determine how repeated low-dose exposures of house finches to MG influence host responses and resistance to a secondary high-dose challenge. MG-naive house finches were given priming inoculations that varied in number of exposures and ranged in dose from 101 to 105 pathogen color changing units. Resulting pathogen load over the course of infection was significantly affected by both dose and number of exposures, while disease severity was influenced by dose alone. All birds were then given a secondary high-dose (105) challenge to assess the level of protection generated by priming inoculations. All priming treatments showed significant protection to high dose challenge relative to birds that had not been previously exposed to MG. Strikingly, in some cases, repeat low-dose exposure to MG, a proxy for what birds likely experience in the wild while feeding, provided complete protection against a high dose challenge. Our results suggest that bird feeders, which serve as a source of infection in the wild, may also act as “immunizers”, with important consequences for disease dynamics.
