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Studies on infection-induced immunosuppression in the chicken

Nandapalan, N. (1981) Studies on infection-induced immunosuppression in the chicken. PhD thesis, Murdoch University.

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Commercial broiler chickens in Western Australia were investigated for the presence of selected sub-clinical viral infections by serological tests and for evidence of altered immune competence using a range of immunological parameters. These chickens were found to be exposed to at least IBDV, avian adenovirus and avian reovirus. The same chickens were also found to have impaired immune functions as evidenced by suppressed antibody response to SRBC and delayed allograft rejection at 28 days of age. Other effects suggestive of immunosuppression such as the reduction in the lymphoid organ/body weight ratio were also found in these chickens.

Various serological tests were used to detect the prevalence of antibodies to the selected viruses. Of the tests used, the ELISA detected higher prevalence of antibodies to these viruses and appeared to be the most suitable test for screening purposes and for IB serology. A commercial vaccine was found to be satisfactory as antigen for the IB virus antibody assay by the ELISA test.

Selected viruses were later investigated for possible immunosuppressive properties in laboratory raised chickens. An Australian strain of IBDV showed sporadic effects on body weight, bursal atrophy and suppression of immune response to standard antigens. The bursal atrophy following infection of day-old chickens was more severe in SPF chickens than conventional chickens. Twenty eight days following infection no evidence of bursal recovery was evident in the SPF chickens but was apparent in the conventional chickens. Immunosuppression occurred in both 1-day-old infected and 30-day-old infected chickens although the latter showed immunosuppression of shorter duration. In the 1-day-old infected chickens, the IgG response to SRBC and NDV was more affected than the IgM response. In addition to the impairment of humoral immune function, some evidence for suppression of CMI function was also seen in the conventional chickens of both age groups. The distribution of various lymphocyte subpopulations was only sporadically affected except in the case of light chain bearing lymphocytes in the peripheral blood.

Reovirus infection was only associated with mild and sporadic changes. The immune response to SRBC was marginally depressed but that to NDV was normal. Evidence for a possible enhancement of CMI was also obtained in allograft rejection tests.

As in the case of reovirus infection, adenovirus infection did not cause any consistent effect on the immune system. However, sporadic changes in body weight and transient medullary depletion was seen in the bursal follicles up to 14 days after infection but no influence on the immune response to standard antigens could be detected.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Penhale, William and Wilcox, Graham
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