As a person who has worked most of the time on viral diseases of poultry l can say that viral diseases on their own without any bacterial complications are major disease problems of poultry. It is only in IBD that you have heterophilic infiltration of any tissue among the viral diseases of poultry. The infiltration is not caused by bacterial complication otherwise the clinical signs and lesions will be variable. You may note that all bacterial diseases of poultry are characterized by enlargement of both the liver and spleen. Liver enlargement can only be found in tumor diseases caused be viruses. Spleen enlargement occurs in viral tumours too and in lymphocidal viral diseases also affecting bursar and thymus but this is quickly followed by atrophy of these organs. Atrophy of the lymphoid organs has not been described for any bacterial disease. I hope that this makes to you. The lesions of bacterial diseases  do  not in any way conflict with

or get superimposed on those of viral diseases. Thank you

Thank you, my professor. It is interesting to note your observation, especially about the heterophilic infiltration which is unique to IBD. What could be responsible for the heterophil recruitment? There seems to be an aspect of the pathogenesis to be explored here. Are there commensal microflora in the healthy bursa with increased pathogenicity after viral colonization? Looking for answers.  

This could be investigated.But you need to note that in a biological system one plus one is not always two. Heterophilic infiltration may not always be due to bacterial inflammation. In IBD this occurs in the bursa only on days 3 and 4 post challenge, that is at inflammatory stage when the bursa is markedly enlarged. The bursa opens into the intestines which are also inflamed without heterophilic infiltration in IBD. Does the bursa have its own specific microflora when it is a diverticulum of the rectum?

Error, please the bursa is a diverticulum of the colon not rectum which many Scientists believe does not exist in chickens