ARTICLE 78 FEED & ADDITIVE MAGAZINE November 2025 Ocular pathway (dust) Respiratory pathway (dust) Cloacal pathway (dust, litter) Eggshell pores Contamination Pathways Examples of Clinical Signs Dermal pathway (dust, litter) Scratches Pododermatitis RESPIRATORY Aerosacculitis Sepsis: pericarditis, perihepatitis, etc. Ovaritis Salpingitis Infectious skin lesions (cellulitis) Pododermatitis Omphalitis Head swelling Gazeous ceca Diarrhea Foamy droppings ORAL CLOACAL OCULAR DERMAL EGGSHELL PORES Oral pathway (water, feed, dust) E. coli contamination can occur at a very early stage, even during the egg phase. If breeding birds are infected, vertical transmission may occur either through the genital tract during egg formation, or via eggshell contamination, eggshell’s pores (30 µm) being permeable to bacteria such as E. coli (≈ 2–3 µm). In adult birds, contamination most commonly occurs via the respiratory route, through inhalation of contaminated dust. Water for drinking or feed can also serve as vectors of contamination. E. coli can cause localized infections, or may lead to septicemia after adhering to mucosal surfaces and entering the bloodstream. Within the intestinal tract, APEC initially adhere to enterocytes using their pili, then release exotoxins that trigger a strong inflammatory response, resulting in the symptoms previously described. However, even after death, APEC continue to release endotoxins, which are responsible for the symptoms of colibacillosis (Figure 1). The infection spreads rapidly within a poultry flock and its housing environment, as birds act as effective E. coli “fermenters”. Infected birds excrete large quantities of E. coli in their feces, where the bacteria can multiply quickly. In confined environment, dust is mostly composed of suspended fecal particles (up to 95% of dust particles). As a result, pathogens excreted in droppings are dispersed throughout the environment (air, floors, walls, farming equipment) via dust, leading to widespread contamination of Figure 1. Overview of E. coli contamination pathways and example of associated clinical signs of colibacillosis ©Lallemand Illustration of some clinical signs of colibacillosis in poultry
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