title: Reduced serologic response to avian influenza vaccine in specific-pathogen-free chicks inoculated with Cryptosporidium baileyi.
abstract: Immunosuppression in chickens as a consequence of Cryptosporidium baileyi infection may compromise the effectiveness of vaccination for control of avian influenza (AI) H5N1. In a 13-wk study using 260 specific-pathogen-free chicks, immunological response and bursa weight:body weight ratios following vaccination against AI strain H5N1 were compared between uninfected and C baileyi-infected birds. The four experimental treatments were the following: infection with C. baileyi (5 x 10(5) oocysts dosed orally on day 0); C baileyi infection + vaccination against H5N1 (0.3 ml inactivated vaccine administered subcutaneously on day 7 and day 21; CB+VAC); vaccination only (VAC); and sham infection/vaccinations using sterile distilled water (control). At weekly intervals serum samples were analyzed by hemagglutination inhibition assay (HI), and five chicks/group were euthanatized for determination of bursa weights. In all but week 8, proportional bursa weights (bursa weight/body weight) were lower for CB+VAC chicks than for VAC chicks (i.e., the bursa index was below 1.0; average 0.81). Throughout the 13 wk, HI titres were lower (P < 0.01) in CB+VAC than in the VAC group, and compared with VAC, chicks in CB+VAC had a slightly shorter period of negative seroconversion. These data indicate bursal atrophy and immunosuppressive effects of C. baileyi infection on day-old chicks vaccinated against AI strain H5N1 and suggest that C. baileyi infection in chicks may increase the host susceptibility to AI virus.
authors.affiliation: National Animal Protozoa Laboratory, College of Veterinary Medicine, China Agricultural University, Beijing 100094, China.
authors.forename: Y-X
authors.initials: YX
authors.lastname: Hao
authors.forename: J-M
authors.initials: JM
authors.lastname: Yang
authors.forename: C
authors.initials: C
authors.lastname: He
authors.forename: Q
authors.initials: Q
authors.lastname: Liu
authors.forename: Tim A
authors.initials: TA
authors.lastname: McAllister
mesh_terms: D000818:Animals; D000914:Antibodies, Viral / Q000097:blood; D002060:Bursa of Fabricius / Q000033:anatomy & histology / Q000254:growth & development; D002645:Chickens; D003457:Cryptosporidiosis / Q000276:immunology / Q000662:veterinary*; D003458:Cryptosporidium / Q000276:immunology*; D005243:Feces / Q000469:parasitology; D053124:Influenza A Virus, H5N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology*; D005585:Influenza in Birds / Q000276:immunology* / Q000517:prevention & control; D009929:Organ Size; D013047:Specific Pathogen-Free Organisms; D013997:Time Factors; D015430:Weight Gain
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines