Preliminary Evidence on Passage Attenuation of Orthoavulavirus javaense Genotype VII.1.1 and Its Potency as a Living Vaccine Candidate

Abstract

Newcastle disease (ND) is one of the most significant poultry viral diseases threatening the poultry industry worldwide. Despite mass vaccination against ND, genotype VII.1.1 epidemics in vaccinated and non-vaccinated flocks are still recorded, indicating an urgent need to generate a new vaccine candidate. In this study, the live Orthoavulavirus javaense (AOAV-1) genotype VII.1.1 strain (CH-EGY-GIZA-VVTNRC-2021) (Genbank accession number MW603772) was attenuated by combining passaging with limiting 10-fold dilutions in the allantoic cavity of embryonated hens eggs for 20 passages. The attenuated virus was used to vaccinate 20 SPF chicks and its protective efficacy was checked. Intracerebral pathogenicity index (ICPI) of the attenuated strain was 0.2, the mean death time (MDT) was 120 hours and infectvity titer was 7 log10 EID50/ml compared to 1.97 ICPI, 36 hours MDT, and 9.5 log10 EID50/ml of the original strain. The attenuated AOAV-1 was protective in vaccinated chicks by means of HI antibody response and protection from heterologus virulent challenge while showing little to no residual pathogencity. Histopathological inspection showed less severe pathological lesions in vaccinated challenged chickens than in nonvaccinated challenged chickens. Quantitation of viral loads following challenge indicated reduction of viral loads shed from birds vaccinated with the attenuated AOAV-1 virus. These preliminary insights collectively underline a new hope for the attenuation of live AOAV-1 genotype VII.1.1 as a vaccine candidate that can be used to control ND outbreaks in Egyptian poultry.