title: Chicken embryo lethality assay for determining the virulence of Riemerella anatipestifer isolates.
abstract: Riemerella anatipestifer is the causative agent of polyserositis and septicaemia in waterfowl. Twenty-one serotypes have been reported, and there is a strong variation in virulence between strains according to serotype or strain. However, little information is available to assess virulence, such as virulence-associated genes; thus, it is difficult to estimate the risk from field strains. Hence, we established a chicken embryo lethality assay (ELA) model to determine the virulence of R. anatipestifer strains. Three virulent strains (RA T1, RA T7, and V-1) and three avirulent strains (Av-1, Av-2, and Av-3), which were confirmed by duck challenge, were used to perform the ELA. Inoculating 10(2) to 10(4) colony-forming units into the allantoic cavity of 10-day-old embryos discriminated between virulent and avirulent strains based on mortality. Differences in invasion rates into embryonic tissues were found between the RA T1 and Av-1 strains. The maximum colony-forming units of the RA T1 strain were about 1000 times higher than those of the Av-1 strain in the tissue invasion rate for 4 days. We found that the virulent strains killed embryos at mortality rates ≥ 50% during the first 3 days after inoculation and that the avirulent strains had death rates of ≤ 20% over 5 days. These results obtained by repeated testing suggest that the ELA could be used as a first-line screening method to determine the virulence of R. anatipestifer strains.
authors.affiliation: Department of Infectious Diseases & Avian Diseases, College of Veterinary Medicine and Research Division of Influenza Korea Zoonosis Research Institute, Chonbuk National University, Jeonju , South Korea.
authors.forename: Hye-Suk
authors.initials: HS
authors.lastname: Seo
authors.forename: Se-Yeoun
authors.initials: SY
authors.lastname: Cha
authors.forename: Min
authors.initials: M
authors.lastname: Kang
authors.forename: Hyung-Kwan
authors.initials: HK
authors.lastname: Jang
mesh_terms: D000818:Animals; D001681:Biological Assay / Q000379:methods / Q000662:veterinary*; D002642:Chick Embryo; D015169:Colony Count, Microbial / Q000662:veterinary; D004372:Ducks; D045826:Flavobacteriaceae Infections / Q000401:mortality / Q000662:veterinary*; D011201:Poultry Diseases / Q000382:microbiology* / Q000401:mortality; D060494:Riemerella / Q000472:pathogenicity*; D013045:Species Specificity