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.
Abbreviations: AI = avian influenza; AIV = avian influenza virus; BF = bursa of Fabricius; BI = bursa index; CB = treatment in which chicks were dosed orally with C. baileyi oocysts; CB VAC = treatment in which chicks received C. baileyi oocysts on day 0 followed by vaccination against avian influenza H5N1 on days 7 and 21; CON = control protocol; HI = hemagglutination inhibition assay; pBF = proportional bursa weight; SPF = specific-pathogen-free; VAC = treatment in which chicks were vaccinated on days 7 and 21 against avian influenza virus (no C. baileyi infection)
Nota de Investigación—Reducción de la respuesta serológica a la vacuna de influenza en aves libres de patógenos específicos inoculadas con Cryptosporidium baileyi.
La inmunosupresión en aves como consecuencia de la infección con Cryptosporidium baileyi puede comprometer la efectividad de la vacunación en el control de la influenza aviar causada por la cepa H5N1. En un estudio durante 13 semanas usando 260 aves libres de patógenos específicos, se comparó la respuesta inmunológica y la proporción del peso de la bolsa:peso corporal después de la vacunación con la cepa H5N1 de influenza aviar en aves no infectadas e infectadas con C. baileyi. Los cuatro grupos experimentales fueron: Infección con C. baileyi (5 × 105 oocistos administrados oralmente al día 0); infección con C. baileyi y vacunación con vacuna de influenza H5N1 (0.3 ml de vacuna inactivada administrada por vía subcutánea a los 7 y 21 días de edad); grupo vacunado contra influenza, y grupo control no vacunado, no infectado. A intervalos semanales se analizaron las muestras de suero mediante la prueba de inhibición de la hemoaglutinación y 5 aves de cada grupo fueron sacrificadas para la evaluación del peso de la bolsa y el peso corporal. Con excepción de la semana 8, en todas las semanas l
