Effects of Co-infection on Pathogen Shedding in Rabbits

In the field of epidemiology, “shedding” refers to the release of pathogenic material from an infected person’s body into their surrounding environment where the infection can spread to other individuals. “Supershedding” occurs when infected individuals shed a greater quantity of infectious material into an environment for a longer duration of time than the average host. Hosts that are co-infected with multiple pathogens at the same time can spread disease to others, which possibly leads to these supershedding events. However, it remains uncertain how immune response to co-infection influences shedding.

CEID’s Ashutosh Pathak and his fellow researchers utilized laboratory experiments to examine this co-infection and shedding dynamic. These experiments focused on the shedding of respiratory bacterium, Bordetella bronchiseptica, in rabbits additionally infected with one or two species of gastrointestinal helminths. Gastrointestinal helminths are parasitic worms that infect the digestive tract. Results from the co-infected rabbits were compared against rabbits that were only infected with the B. bronchiseptica bacteria

The rabbits, who were already infected with the B. bronchiseptica bacteria, were then experimentally co-infected with one or both of the gastrointestinal helminths (Trichostrongylus retortaeformis and Graphidium strigosum). The study focused on to what extent helminths may impact B. bronchiseptica shedding over time, specifically exploring any variations between helminth species and if host immune response may explain shedding patterns. 

In order to examine the impact of helminth co-infections, four experimental groups were investigated: rabbits infected with B. bronchiseptica only (B), rabbits infected with B. bronchiseptica and the Graphidium strigosum helminth (BG), rabbits infected with B. bronchiseptica and the Trichostrongylus retortaeformis helminth (BT), and rabbits infected with B. bronchiseptica and both helminths (BTG). To measure bacteria shedding, the rabbits had direct contact with a petri dish over a fixed time.

The results found that rabbits that were co-infected with one or both of the helminths (BG, BT, BTG) shed significantly more Bordetella bronchiseptica compared to the rabbits only infected with the bacteria (B). The hosts co-infected with helminths produced supershedding events more frequently and more intensely leading to a greater number of bacteria shed. The research team produced an “infection-immune” model to try to understand the impact of immune response on shedding variation. This model displayed the variation in shedding duration and quantity can be explained by the effect of the two helminths on immune response in clearing bacteria from the respiratory tract. Overall, the data from this study suggests that co-infected hosts play an important role in shedding variation and displays the relationship between helminths and B. bronchiseptica.

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By: Brenna Daly