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Reduced Serologic Response to Avian Influenza Vaccine in Specific-Pathogen-Free Chicks Inoculated with Cryptosporidium baileyi.

Hao, Y-X., Yang, J.M., He, C., Liu, Q., and McAllister, T.A. (2009). "Reduced Serologic Response to Avian Influenza Vaccine in Specific-Pathogen-Free Chicks Inoculated with Cryptosporidium baileyi.", Avian Diseases, 52(4), pp. 690-693. doi : 10.1637/8370-052608-Reg.1  Access to full text

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 × 105 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.

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