Livestock-related microbial air pollution:residential exposure and health effects

Livestock-related microbial air pollution is underexplored despite its suggested public health relevance based on epidemiological findings worldwide. The objectives of this thesis were to characterize livestock-related microbial exposures in air at residences, to perform and evaluate spatial modelling, and to study exposure-response relations. Residential exposures of multiple livestock-related microbial air pollutants including zoonotic pathogens, commensal bacteria, antimicrobial resistance genes and endotoxin (pro-inflammatory component of bacterial origin), were quantified through exposure assessment campaigns. Associations with livestock-related characteristics of the surroundings were analyzed. For endotoxin, two modelling approaches (Land-Use Regression and dispersion) were evaluated and applied to quantify residential exposure of participants of a health survey enabling exposure-response analyses. Data on respiratory symptoms and diseases, lung function and atopic sensitization was used. The exposure assessment campaigns revealed measurable exposures in air to livestock-related microbial air pollutants at residences. Clear spatio-temporal variation was observed, exposure levels were markedly higher in livestock dense areas. Levels were related to the number of livestock farms present in the surroundings and distances to these farms, distinct attribution differences between farm-types were found. Health analyses showed associations between residential exposure to livestock farm emitted endotoxin with respiratory effects and atopic sensitization. This thesis indicates the importance of infectious as well as non-infectious aspects of microbial emissions from livestock farms. Advancements made in exposure assessment and modelling of microbial air pollution open up a myriad of research possibilities from both a human health as veterinary perspective. Improving insights in microbial air pollution is key for protecting (public) health.