Ultrastructural changes of chick bursal epithelial cells experimentally infected with Cryptosporidium sp

The ultrastructural changes in the bursal epithelial cells of chickens infected with Cryptosporidium sp. were investigated. The principal features were as follows: deep invaginations or indentations of the nucleus with separate lobulations in some instances, nucleolar hypertrophy with formation of reticular or open nucleolonema, increase or swelling of mitochondria, increase in coated vesicles, ribosomes and well-developed rough endoplasmic reticulum (RER), increase in mitochondrial-RER association, appearance of small, smooth-membraned vacuoles in the apical cytoplasm, and formation of electron dense fibres. In addition, nuclear bodies, thin-shelled or ring-shaped nucleoli, nucleolar segregation, nucleolar margination, ribo-some-lamella complex, microtubuloreticular complex, disaggregation of polysomes and vesiculation of RER were rarely observed. Most of the ultrastructural changes observed here seemed to be related to a heightened metabolic activity, namely active or increased protein synthesis, in response to the parasitism.