Stage-specific remodeling of the pulmonary microenvironment during Paragonimus proliferus infection in a rat model

Paragonimiasis, a food-borne zoonosis caused by Paragonimus spp., can cause severe pulmonary inflammation and fibrosis. However, relationships among the host, parasite and lung microbiome at defined infection stages remain poorly understood. We compared independent groups of rats sampled at 14, 28 and 42 days post-infection (dpi), together with a separate group sampled after triclabendazole (TCBZ) treatment. Histopathological and molecular analyses were combined with multi-region (5R) 16S rRNA gene sequencing and fluorescence in situ hybridization (FISH). Groups sampled at later post-infection time points showed greater pulmonary inflammation and collagen deposition, with the highest values in Pp-42d; both outcomes were lower in Pp-TCBZ than in Pp-42d. Th1-, eosinophil-, Th2- and Treg- associated markers differed among experimental groups. TLR4/NF-κB -related protein expression and pulmonary microbial profiles also differed among groups including enrichment of taxa such as Lactobacillus in infected animals. FISH detected bacterial signals within inflammatory lesions and Lactobacillus-associated signals spatially associated with parasite eggs. These repeated cross-sectional findings identify stage-associated differences in pulmonary pathology, immune markers and microbiota during P. proliferus infection, together with lower pathological measures in the Pp-TCBZ group than in the untreated Pp-42d group. The egg-associated bacterial signals warrant further investigation but do not establish a functional host-parasite-microbiome mechanism.