Evaluation of Chicken Astrovirus Breeder Vaccine Candidate

Introduction: Chicken astrovirus (CAstV) is a ubiquitous agent infecting global broiler production, mainly affecting embryos and neonates, with some highly pathogenic (hp) strains causing hatchery losses (up to 69%) and fatal kidney disease with visceral gout. There are two serogroups of CAstV, A and B; most diseases have been associated with the B serogroup, which is subdivided into subgroups via capsid gene genotyping.

Methods: The CAstV-11672 (subgroup Bi) strain was administered to in-lay broiler breeder hens as a live breeder vaccine candidate. Sera were monitored weekly for seroconversion via ELISA. Eggs were collected from seroconverted and control hens, and were synchronised and incubated to hatch. Hatchlings in isolators were challenged with one of three hp strains belonging to subgroups Bi, Biii and Biv. The chicks were visually monitored for disease development; their CAstV levels were monitored by real time RT-qPCR; and their weight and development of kidney lesions by days four and ten (termination) were monitored.

Results: Thelevels of CAstV seroconversion in hens were low after oral inoculation but increased significantly after intramuscular inoculation. The levels of anti-CAstV antibodies detected in egg yolks were approximately half that of the hens. The weights of chicks with maternally-derived antibodies (matABs) were significantly higher at day 10 after being challenged with hp strains from the Bi and Biii subgroups. The chicks with matABs showed no kidney lesions at day 4 from any of the hp strains, whereas the chicks without matABs had substantial numbersof kidney lesions at day 4, which were statistically significant by day 10.

Conclusions: The CAstV-11672 strain elicited a strong immune response in adult birds, with successful the transmission of matABs that protected the hatchlings from challenges with hp strains of CAstV, resulting in the prevention of kidney damage and higher body mass compared to chicks without anti-CAstV matABs. CAstV-11672 appears to be a successful candidate for a CAstV breeder vaccine.