Sequential pathological changes of fowl typhoid in plasmid cured vaccinated and unvaccinated chickens following challenge with Salmonella gallinarum var duisburg*

The gross and microscopic changes were primarily seen in liver, spleen, heart and bursa of Fabricius. Typical bronze discolouration of liver was observed only in unvaccinated challenged birds in comparision to necrotic foci in the liver and spleen seen in the first week of infection in the vaccinated birds. Microscopically, necrotic changes of lymphoid organs were prominently seen in unvaccinated birds whereas vaccinated birds revealed RE cell hyperplasia and secondary follicle formation. The results indicated that vaccination with plasmid-cured S. Gallinarum strain had protective action against the development of lesions in different organs and there was tendency towards early regression.