Attenuated live infectious bronchitis virus QX vaccine disseminates slowly to target organs distant from the site of inoculation

•IBV-QX vaccine and virulent progenitor have comparable RNA titers in the trachea.•IBV-QX vaccine shows delayed induction of lesions in the respiratory tract.•IBV-QX vaccine has reduced ability to disseminate from the site of inoculation to other target tissues.•IBV-QX vaccine displays no nephropath...

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Published in:	Vaccine Vol. 38; no. 6; pp. 1486 - 1493
Main Authors:	Laconi, A., Weerts, E.A.W.S., Bloodgood, J.C.G., Deniz Marrero, J.P., Berends, A.J., Cocciolo, G., de Wit, J.J., Verheije, M.H.
Format:	Journal Article
Language:	English
Published:	Netherlands Elsevier Ltd 05-02-2020 Elsevier Limited The Author(s). Published by Elsevier Ltd
Subjects:	Animals Antigens Attenuation Bacterial infections Birds Broilers Bronchitis Chickens Cloaca - virology Coronaviridae Coronavirus Infections - prevention & control Coronaviruses Eggs Female Gene expression Genotypes Immunization Infections Infectious bronchitis virus Infectious bronchitis virus - immunology Infectious bronchitis virus - pathogenicity Infectious bronchitis virus - physiology Inoculation Intestine Kidney - pathology Kidney - virology Kidneys Laboratories Lesions Male Nephropathogenicity Organs Phenotypes Poultry Protein expression Proteins Replication Respiratory diseases Ribonucleic acid RNA Tissue Distribution Trachea Trachea - pathology Trachea - virology Ureter Vaccine Vaccines Vaccines, Attenuated - administration & dosage Vaccines, Attenuated - pharmacokinetics Variance analysis Viral Vaccines - administration & dosage Viral Vaccines - pharmacokinetics Virulence Virus Replication Viruses United States > US Netherlands Germany Nephropathogenicity Attenuation Vaccine Broilers Virulence Infectious bronchitis virus
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Summary:	•IBV-QX vaccine and virulent progenitor have comparable RNA titers in the trachea.•IBV-QX vaccine shows delayed induction of lesions in the respiratory tract.•IBV-QX vaccine has reduced ability to disseminate from the site of inoculation to other target tissues.•IBV-QX vaccine displays no nephropathogenicity in SPF broilers.•Ascending virus transport seems to contribute to kidney infection. Infectious bronchitis (IB) is a highly contagious respiratory disease of poultry, caused by the avian coronavirus infectious bronchitis virus (IBV). Currently, one of the most relevant genotypes circulating worldwide is IBV-QX (GI-19), for which vaccines have been developed by passaging virulent QX strains in embryonated chicken eggs. Here we explored the attenuated phenotype of a commercially available QX live vaccine, IB Primo QX, in specific pathogens free broilers. At hatch, birds were inoculated with QX vaccine or its virulent progenitor IBV-D388, and postmortem swabs and tissues were collected each day up to eight days post infection to assess viral replication and morphological changes. In the trachea, viral RNA replication and protein expression were comparable in both groups. Both viruses induced morphologically comparable lesions in the trachea, albeit with a short delay in the vaccinated birds. In contrast, in the kidney, QX vaccine viral RNA was nearly absent, which coincided with the lack of any morphological changes in this organ. This was in contrast to high viral RNA titers and abundant lesions in the kidney after IBV D388 infection. Furthermore, QX vaccine showed reduced ability to reach and replicate in conjunctivae and intestines including cloaca, resulting in significantly lower titers and delayed protein expression, respectively. Nephropathogenic IBVs might reach the kidney also via an ascending route from the cloaca, based on our observation that viral RNA was detected in the cloaca one day before detection in the kidney. In the kidney distal tubular segments, collecting ducts and ureter were positive for viral antigen. Taken together, the attenuated phenotype of QX vaccine seems to rely on slower dissemination and lower replication in target tissues other than the site of inoculation.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 Contributed equally. Department of Comparative Biomedicine and Food Science, University of Padua, Legnaro (PD), Italy.
ISSN:	0264-410X 1873-2518 1873-2518
DOI:	10.1016/j.vaccine.2019.11.064