A study of the chicken astrovirus pathobiology in the emerging white chicks hatchery disease

Abstract

Chicken astroviruses (CAstVs) has been associated with an emerging disease of broiler chicks named white chicks hatchery disease. Adult birds typically show no obvious clinical signs of infection, although some broiler breeder flocks have experienced slight egg drops. Substantial decreases in hatching are experienced over a two-week period, with an increase in mid-to-late embryo deaths, chicks too weak to hatch and pale, runted chicks with high mortality. CAstV is an enteric virus, and strains are typically transmitted horizontally within flocks via the faecal–oral route; however, dead-in-shell embryos and weak, pale hatchlings indicate vertical transmission of the strains associated with white chicks hatchery disease. Hatch levels are typically restored after two weeks when seroconversion of the hens to CAstV has occurred. Currently, there are no commercial vaccines available for the virus; therefore, the only means of protection is by good levels of biosecurity. This thesis aimed to construct a reverse genetics system to introduce the enhanced green fluorescent protein (eGFP) into the CAstV strain, VF11-66, which is associated with white chicks hatchery disease and to utilise the fluorescently tagged CAstV to study the tissue tropism and infection in the adult birds, and identify the route of transmission into the developing egg. However, due to the numerous challenges faced with the cloning of the virus genome and virus rescue, this was not possible. Instead, the non-recombinant VF11-66 strain was used to infect the adults to study the CAstV infection. From this study, it was identified that CAstV most commonly infected the organs belonging to the enteric system in the adult birds and that the virus was transmitted into the egg via the reproductive organs, in particular the ovules. Furthermore, this study demonstrated the successful reproduction of white chicks hatchery disease in embryos inoculated into the yolk sac with CAstV at a low titre of 1 x 103.5 50% tissue culture infectious dose (TCID50).

Thesis is embargoed until 31 July 2024.

Date of Award	Jul 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Department of Agriculture, Environment and Rural Affairs
Supervisor	Ken Lemon (Supervisor), Irene R. Grant (Supervisor) & Victoria Smyth (Supervisor)