Molecular characterization of the effects of essential oils on mRNA gene expression related to proinflammatory and antiviral pathways, virus load, and antibody production in chickens vaccinated against Newcastle disease virus, infectious bursal disea

This study evaluated the effects of essential oils (EOs) on pro-inflammatory and antiviral mRNA expression, viral load, and serum antibody levels in broiler chickens, with and without vaccination. Four experiments were conducted using live attenuated vaccines for Newcastle disease virus (NDV), infectious bursal disease virus (IBDV), and infectious bronchitis virus (IBV): EXP1 (unvaccinated control), EXP2 (NDV), EXP3 (IBDV), and EXP4 (IBV). Each experiment included three treatments: T1 (no EO), T2 (a blend of Lippia origanoides, Rosmarinus officinalis, and Lippia alba), and T3 (Lippia alba alone). Birds were vaccinated at 14 days post-hatch, and tracheal and bursal samples were collected on days 21 and 28 to evaluate mRNA expression of NF-κB, IL-1β, TLR3, TLR7, MDA5, IFN-β, OAS, and PKR, as well as viral load and antibody titers. In the trachea, both T2 and T3 modulated antiviral gene expression in EXP1 and EXP2, with significant up-regulation of TLR3, IFN-β, and OAS on day 21, as well as additional effects on day 28. In EXP4, OAS was up-regulated by both treatments on day 21, while TLR3, MDA5, and PKR were enhanced on day 28. In the bursa, IFN-β was up-regulated in EXP1 on day 21 and broader activation occurred by day 28. In EXP3, TLR7 increased on day 21, and TLR3 and MDA5 (T2) on day 28. Viral load decreased with T3 in NDV (EXP2) at both time points and in IBDV (EXP3) on day 21, with no significant change for IBV (EXP4). Antibody titers were unchanged on day 21 but increased on day 28 for NDV and IBDV (T2 and T3) and for IBV (T3). These findings suggest that EO supplementation via spray application may modulate antiviral pathways, reduce viral replication, and enhance humoral responses, supporting its potential as a natural immunomodulator to improve antiviral protection in poultry.