Disrupted gut microbiota, suppressed inflammation, and impaired bone health in turkey poults challenged with Histomonas meleagridis and co-infected with Eimeria and E. coli

Histomonas meleagridis (HM) induces severe inflammatory and necrotic lesions in the ceca and liver of turkeys. It is shown that some pathogens may interact with the progress of HM. Shifts in microbial communities can impair intestinal barrier function, allowing bacterial translocation to systemic organs. This study investigated the effects of H.meleagridis challenge and coinfections with Eimeria (EM) and E.coli on turkeys' gut microbiota and bone health. Three hundred and sixty day-old male turkey poults were placed in six treatments: NC, negative control; HM, challenged with 10⁵ HM/bird at d 18; EM, inoculated with 8,000 oocysts of E. adenoeides and E. meleagrimitis at d 22; E. coli, challenged with 10⁹E. coli/bird at d 18; HM+EM, challenged with 10⁵ HM/bird at d 18, and 8,000 oocysts of E. meleagrimitis and E. adenoeides at d 22 and HM+E. coli, challenged with 10⁵ HM and 10⁹E. coli /bird at d 18. The trial lasted for 28 days. H. meleagridis challenge decreased body weight, feed intake, weight gain, bone density, total tissue and lean weight, increased feed conversion ratio, mortality, cecal wall thickness, and ileal crypt depth (P < 0.05). Eimeria Co-infection reduced duodenal and jejunal villus height, jejunal VH/CD, and upregulated tight junction gene expression (P < 0.05). HM and co-infection interactions decreased ileal villus height, increased crypt depth in HM+EM, increased cecal muscle thickness in HM+E. coli, reduced bone total volume, cortical and trabecular BMD, and number of closed pores in HM+E. coli. Microbial community shifts included a higher Firmicutes/Bacteroidetes ratio in HM, with reduced Ruminococcaceae abundance in HM (∼2 %) compared to NC (∼10 %) and increased Leuconostocaceae in HM. Weighted and unweighted UniFrac analyses revealed significant group separations in HM and HM+E. coli. In conclusion, HM markedly impaired survival and growth regardless of co-infection with Eimeria or E. coli. Co-infections had slight additional effects, mainly altering intestinal histology, pathogen colonization, and microbiota.