Co-infection of Cystoisospora suis with enterotoxigenic Escherichia coli synergistically increases pathogenicity in weaned piglets.

backgroundWhile Cystoisospora suis is well established as a primary pathogen in suckling piglets, it can also infect weaned piglets. In this context, we investigated its co-infection with enterotoxigenic Escherichia coli (ETEC), a major cause of post-weaning diarrhea.

methodsWeaned piglets were randomly divided into four groups: a negative control group (NC), an ETEC single-infection group (EC), a C. suis single-infection group (CS), and a co-infection group (EC-CS). Following infection, clinical symptoms were recorded, and samples were collected to evaluate intestinal histopathological damage, expression of tight junction protein genes, inflammatory cytokine levels, and gut microbiota changes.

resultsCompared to single-infection groups, piglets in the co-infection group exhibited more severe diarrhea, growth retardation, and intestinal damage, characterized by near-total loss of villus and crypt structures. Co-infection significantly impaired intestinal barrier function, as evidenced by a marked downregulation of claudin-1 messenger RNA (mRNA) expression compared to both single-infection groups, and triggered more intense local and systemic inflammatory responses. 16S ribosomal RNA (rRNA) sequencing revealed that co-infection exacerbated gut microbiota dysbiosis and promoted the proliferation of pathogenic bacteria.

conclusionsCo-infection with C. suis and ETEC exerts a synergistic pathogenic effect in weaned piglets. The mechanism involves a vicious cycle of intestinal barrier disruption, microbiota dysbiosis, and amplified inflammatory responses. These findings provide a novel theoretical basis for the clinical prevention and control of complex intestinal co-infections.