title: Pathogenicity of wild-type and small-colony variants of Streptococcus equi subsp. zooepidemicus in layer chickens.
abstract: Wild-type (WT) and small-colony-variant (SCV) strains of Streptococcus equi subsp. zooepidemicus have recently been isolated from a layer flock in Denmark experiencing high mortality. To investigate the disease-causing potential of SCV compared with WT, a 2-week long infection study was performed in 45-week-old brown layer chickens. Four groups of 11 chickens each were inoculated with a WT or SCV strain by the intravenous or intra-tracheal route: WT-IV, SCV-IV or WT-IT, SCV-IT, respectively. Clinical signs were observed in most chickens in the WT-IV group (9/11). Mortality was observed in the SCV-IV (4/11) and WT-IV (2/11) groups. Ten chickens in the WT-IV and WT-IT groups, respectively, developed gross lesions including oophoritis/peritonitis, hepatitis and airsacculitis cervicalis. Bronchopneumonia was common in the SCV-IT group (6/11), and valvular endocarditis in the SCV-IV group (4/11). Histological lesions in liver tissue were frequently observed in the chickens of the SCV-IV group (9/11), followed by the WT-IT (7/11), WT-IV (6/11), and SCV-IT (2/11) groups. The lesions in the SCV-IV group were dominated by deposition of eosinophilic material with infiltration of inflammatory cells (6/9). Bacteriological re-isolation of either strain type was achieved from all chickens of the WT-IV and WT-IT groups, and from nine and seven out of 11 chickens for each of the SCV-IV and SCV-IT groups, respectively. In summary, we were able to reproduce clinical signs and lesions as observed during the natural outbreak, which included an overall initial onset in WT-infected chickens as opposed to a late onset and possible recurring infection seen in the SCV-infected chickens.
authors.affiliation: Department of Veterinary Disease Biology, Faculty of Health and Medical Sciences, University of Copenhagen Frederiksberg C, Denmark.
authors.forename: Krisna
authors.initials: K
authors.lastname: Roy
authors.forename: Magne
authors.initials: M
authors.lastname: Bisgaard
authors.forename: Niels Christian
authors.initials: NC
authors.lastname: Kyvsgaard
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Christensen
authors.forename: Ole Lerberg
authors.initials: OL
authors.lastname: Nielsen
authors.forename: Paritosh Kumar
authors.initials: PK
authors.lastname: Biswas
authors.forename: Susanne Elisabeth
authors.initials: SE
authors.lastname: Pors
authors.forename: Anders Miki
authors.initials: AM
authors.lastname: Bojesen
mesh_terms: D000818:Animals; D001996:Bronchopneumonia / Q000473:pathology / Q000662:veterinary; D002645:Chickens; D003718:Denmark; D004696:Endocarditis / Q000473:pathology / Q000662:veterinary; D008099:Liver / Q000473:pathology; D011201:Poultry Diseases / Q000382:microbiology* / Q000473:pathology*; D013045:Species Specificity; D013290:Streptococcal Infections / Q000401:mortality / Q000473:pathology / Q000662:veterinary*; D018502:Streptococcus equi / Q000472:pathogenicity*