Platelet kinetics in canine ehrlichiosis: evidence for increased platelet destruction as the cause of thrombocytopenia.

A significant (P < 0.025) increase in the mean platelet diameter occurred in five Ehrlichia canis-infected dogs when platelet numbers decreased to 100,000/mul or less. Maximal incorporation of [(75)Se]selenomethionine into platelets of six uninfected dogs was 0.080 +/- 0.019% (mean +/- standard error) and occurred 5 to 6 days after dosage, whereas maximal incorporation was 0.036 +/- 0.004% within 2 to 3 days after dosage in seven chronically infected dogs that had thrombocytopenia. Analysis of the [(75)Se]selenomethionine curves yielded a platelet lifespan of 9 days in uninfected dogs versus 4 days in chronically infected dogs. Thus, megakaryocyte maturation and/or platelet release occurred at an accelerated rate in infected dogs, whereas increased destruction of newly produced labeled platelets diminished their number of peripheral blood. [(51)Cr]sodium chromate-labeled platelet survival was exponential, with a half-life of approximately 1 day in two dogs at 2 to 4 days postinfection and three chronically infected dogs. Platelet survival time was 8 days and rectilinear in four uninfected dogs. Platelet recovery was 39.43 +/- 2.86% in infected dogs as compared with 68.2 +/- 10.72% in uninfected dogs. Whole-body scans of one dog prior to and 7 days after infection showed that labeled platelets were destroyed primarily in the spleen. It is concluded that the thrombocytopenia in E. canis-infected dogs is the result of increased platelet destruction which begins within a few days after infection.