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This study aimed to analyze the genetic relatedness of key antigenic and virulence genes in the attenuated FJ19 strain of infectious laryngotracheitis virus （ILTV）， and to evaluate its safety and immunogenic efficacy in specific-pathogen-free （SPF） chickens， thereby providing valuable groundwork for the development of an attenuated live vaccine derived from the ILTV FJ19 strain. The ILTV FJ19 strain was adapted through allantoic cavity inoculation in chicken embryos， with sequencing confirming immunogenic and virulence genes. Safety tests were assessed in 14-day-old SPF chickens. Protective efficacy was demonstrated by challenging vaccinated chickens （ocular/oral routes at 14 days） with virulent ILTV strain at 21 days post-vaccination （dpv）. Vaccine durability was also determined. After serial passages in 10-day-old SPF chicken embryos via allantoic cavity inoculation， the EID50 values of harvested P0， P1， P2， and P3 viral suspensions were 105.0， 106.5， 106.9， and 106.5·mL-1， respectively. Genetic and phylogenetic analysis revealed： key immunogenic genes （gB， gC， gD， UL32） and virulence-associated genes （gE， gI， TK， ICP4， gG， gH， gK， gL， gM， gN） of FJ19 strain clustered closely with attenuated strains K317， Nobilis Laringovac®， LT Blen， Poulvac ILT®， Laryngo Vac and Chinese virulent isolates LJS09 （2009）， ck/CH/LHLJ/120305 （2012）， WF03 （2019）. Safety assessment demonstrated： Ocular inoculation （104.0 EID50 per bird） caused mild conjunctivitis in 40% of 14-day SPF chickens， while oral administration showed no symptoms. Intratracheal challenge （104.0 EID50 per bird） of FJ19 strain in 21-day-old SPF chickens caused transient respiratory reactions in a minority （30%）， with no severe ILTV-specific symptoms. Efficacy evaluation confirmed： Immunization （0.2 or 1 dose via ocular/oral routes） provided at least 90% protection against intratracheal challenge with virulent WF03 （104.0 EID50 per bird） at 21 dpv， with no clinical signs in immunized groups. However， at least 90% of unimmunized virus-challenged chickens developed characteristic severe ILTV infection symptoms. Vaccine-induced immunity persisted for ≥6 months. The results demonstrated that： The ILTV strain FJ19 achieves high-titer cultivation via allantoic cavity inoculation. Its major antigenic and virulence genes show no significant variation compared to early Chinese isolates and vaccine strains. The FJ19 strain demonstrated excellent safety and immunogenicity in 14-day-old SPF chickens， immunity duration reached 6 months， with oral administration maintaining safety and efficacy. Thus， adaptation to allantoic cavity inoculation of FJ19 strain yielded a virus suspension with optimal safety and immunogenicity， the attenuated ILTV FJ19 strain represents an ideal candidate for oral attenuated live vaccine development.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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