Co-infected hosts, individuals that carry more than one infectious agent at any one time, have been suggested to facilitate pathogen transmission, including the emergence of supershedding events. However, how the host immune response mediates the interactions between co-infecting pathogens and how these affect the dynamics of shedding remains largely unclear. We used laboratory experiments and a modeling approach to examine temporal changes in the shedding of the respiratory bacterium Bordetella bronchiseptica in rabbits with one or two gastrointestinal helminth species. Experimental data showed that rabbits co-infected with one or both helminths shed significantly more B. bronchiseptica, by direct contact with an agar petri dish, than rabbits with bacteria alone. Co-infected hosts generated supershedding events of higher intensity and more frequently than hosts with no helminths. To explain this variation in shedding an infection-immune model was developed and fitted to rabbits of each group. Simulations suggested that differences in the magnitude and duration of shedding could be explained by the effect of the two helminths on the relative contribution of neutrophils and specific IgA and IgG to B. bronchiseptica neutralization in the respiratory tract. However, the interactions between infection and immune response at the scale of analysis that we used could not capture the rapid variation in the intensity of shedding of every rabbit. We suggest that fast and local changes at the level of respiratory tissue probably played a more important role. This study indicates that co-infected hosts are important source of variation in shedding, and provides a quantitative explanation into the role of helminths to the dynamics of respiratory bacterial infections.
Multi-species infections have been suggested to facilitate pathogen transmission and the emergence of supershedding events. However, how the interactions between co-infecting pathogens affect their dynamics of shedding, and how this is related to the host immune response, remains largely unclear. We used laboratory experiments and a modeling approach to examine temporal variations in the shedding of the respiratory bacterium Bordetella bronchiseptica in rabbits challenged with one or two gastrointestinal helminth species. Experimental data showed that rabbits co-infected with one or both helminths shed significantly more B. bronchiseptica by direct contact with an agar petri dish than rabbits with bacteria alone. There was also evidence of synergistic effects when both helminth species were present (triple infection). Co-infected hosts generated supershedding events of higher intensity and more frequently than hosts with no helminths. Model simulations revealed that the two helminths affected the relative contribution of neutrophils and specific IgA and IgG to B. bronchiseptica neutralization in the respiratory tract. In turn, these changes led to differences in the magnitude and duration of shedding among the various types of infection. However, the rapid variation in individual shedding, including supershedding, could not be explained by the interactions between infection and immune response at the scale of analysis that we used. We suggest that local rapid changes at the level of respiratory tissue probably played a more important role. This study provides novel insight into the role of helminths to the dynamics of respiratory infections and offers a quantitative explanation for the differences generated by two helminth species.
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