Eosinophilia in duck embryos induced by an apathogenic strain of duck enteritis virus

An apathogenic strain of duck enteritis virus was injected into the allantoic cavity of duck embryos at 17 or 18 days of incubation. Four to 6 days later, the embryos showed massive infiltration of eosinophilic granulocytes in the spleen. Peroxidase and immunohistochemical labelling showed that the granulocytes were peroxidase-positive and contained major basic protein, and were most likely eosinophils. UltraIstructural examination of the eosinophils demonstrated granules of various sizes and shapes, and granules within the granules. Electron microscopy also showed that splenic macrophages were capable of phagocytosis, indicating that duck embryos, even at 23-24 days of incubation, were capable of responding to infection.