Wavelength-Dependent Reduction of Newcastle Disease Virus Infectivity by Femtosecond Laser Irradiation: An In Ovo Proof-of-Concept Study.

Newcastle disease virus (NDV) causes substantial losses in poultry, and nonchemical approaches for reducing viral infectivity warrant investigation. Ultrafast femtosecond (fs) lasers offer a novel, non-thermal, and photosensitizer-free approach to pathogen inactivation. The primary aim of this study was to evaluate the wavelength-dependent efficacy of femtosecond laser irradiation (370-420 nm) in inactivating NDV, establishing a proof-of-concept for non-chemical viral attenuation using embryonated chicken eggs (ECEs) as a biological model. NDV suspensions were irradiated with 100 fs laser pulses at 370, 385, 400, and 420 nm for 60 min. The treated virus samples (100 µl) were inoculated into specific-pathogen-free (SPF) embryonated chicken eggs at dilutions of 10⁵, 10⁷ and 10⁹ and the viability of the embryo was monitored. Viral infectivity was assessed by embryo mortality and hemagglutination (HA) assays over 168 h. Exposure to 370 nm laser light resulted in > 99.99% reduction in viral infectivity and an estimated ≥ 4-log shift in the infectivity endpoint compared with the control, but complete inactivation was not observed. HA assays showed no protection at 385 and 400 nm on embryo death, but there was partial protection at 420 nm. Temperature monitoring did not show any thermal effects, indicating a non-thermal inactivation mechanism. This study demonstrates the strong antiviral potential of 370 nm femtosecond lasers against NDV; nevertheless, these findings justify further optimization of irradiation dose and independent confirmation by at least three serial passages. Viral antigen integrity, immunogenicity, and protective efficacy must be evaluated separately before any vaccine application.