Abstract
Foot-and-mouth disease virus particles were observed by electron microscopy in the cytoplasm of alveolar secretory cells of the bovine mammary gland after contact exposure of uninfected cows to pigs with foot-and-mouth disease. Virus, contained in membrane-limited vesicles, was released from the basal and peranuclear portions of the cell into the intracellular and extracellular spaces by an exocytotic mechanism similar to that of the release of the milk-fat globule. Virus was released into the lumen from the apical portion of the cell both by membrane-limited vesicles and by the merocrinal exocytosis of casein-associated virus. The lytic release of virus was observed in 20% of the preparations observed.