Avian influenza virus transmission is suppressed in chickens fed Lactobacillus paracasei expressing the 3D8 single-chain variable fragment protein

The 3D8 single-chain variable fragment (scFv) is a mini-antibody sequence with independent nuclease activity that shows antiviral effects against all types of viruses in chickens and mice. In this study, chickens were treated daily with an oral dose of 10⁹ CFU Lactobacillus paracasei (L. paracasei) expressing either a secreted or anchored 3D8 scFv for three weeks. After L. paracasei administration, the chickens were challenged with avian influenza virus (AIV). From each experimental group, three chickens were directly infected with 100 μL of 10^7.5 EID₅₀/mL H9N2 AIV and seven chickens were indirectly challenged through contact transmission. Oropharyngeal and cloacal swab samples were collected at 3, 5, 7, and 9 days post-inoculation (dpi) from AIV-challenged chickens, AIV Shedding titres were measured by quantitative real-time PCR. Contact transmission in the chickens that were fed 3D8 scFv-secreting L. paracasei showed a significant reduction in viral shedding when compared with other groups. These results suggest that L. paracasei secreting 3D8 provides a basis for the development of ingestible antiviral probiotics with activity against AIV.