Ultrastructure of blood platelets in cattle with East Coast fever.

The sequence of ultrastructural changes of bovine platelets during the fatal course of East Coast fever was swelling; formation of vacuoles, pseudopodia, and indentations; then thrombocytorrhexis and degranulation; and finally, thrombocytolysis. These changes led to thrombocytopenia and release of serotonin, resulting in petechiations and pulmonary edema.