Immunopathological effects of co-exposure to ochratoxin A and FAdV-4 in broilers.

1. Immunosuppressive disorders in poultry pose a significant threat to health and productivity. Ochratoxin A (OTA), a mycotoxin and fowl adenovirus serotype 4 (FAdV-4), the causative agent of hydropericardium syndrome and inclusion body hepatitis, are each known for their immunopathological effects. However, little is known about their combined impact on the immune system of poultry.2. This study investigated the synergistic immunosuppressive and pathological effects of OTA and FAdV-4 co-exposure in broiler chickens. A total of 144, one-day-old broiler chicks were randomly divided into six groups and exposed to OTA (200 ppb or 400 ppb), FAdV-4, or their combinations for 35 d. The FAdV-4 inoculum was PCR-confirmed and administered subcutaneously.3. Birds were monitored for clinical signs, mortality, feed intake and weight gain. Immune function was assessed via SRBC antibody titres, PHA-P - induced lymphoproliferation and carbon clearance assay. Gross and histopathological changes in lymphoid organs were also evaluated.4. The OTA exposure led to dose-dependent immunosuppression, with significant reductions (p ≤ 0.05) in humoral and cell-mediated responses, lymphoid organ atrophy and phagocytic dysfunction. The FAdV-4 infection alone caused immunosuppressive effects, which were significantly exacerbated when combined with OTA. Co-exposed birds exhibited severe lymphocytic depletion, pronounced histological lesions and increased mortality.5. The results demonstrated a synergistic immunosuppressive interaction between OTA and FAdV-4 in broiler chickens. This highlighted the need for routine mycotoxin screening in feed and molecular surveillance of adenoviral infections to prevent compounded immunosuppressive effects and economic losses in commercial poultry production.