Platelet dysfunction associated with experimental acute canine ehrlichiosis

To determine whether platelet dysfunction occurs in canine ehrlichiosis, platelet aggregation studies in response to collagen/ epinephrine, thrombin and adenosine diphosphate (ADP) were carried out by the indirect method, using sera from six dogs experimentally infected with Ehrlichia canis . Samples of serum taken before infection and four and 20 days after infection were tested by incubation with platelet-rich plasma from a seronegative healthy dog. Platelet aggregation was significantly inhibited in five of six infected dogs in response to at least one of the agonists used. A significant increase in preaggregation lag time was recorded in response to collagen/ epinephrine in sera taken 20 days after infection from three of five dogs (P<0.05). When compared with the preinfection values, a significant increase of 45 per cent in the mean preaggregation lag time was detected (P<0.05). Maximal relative aggregation responses to ADP decreased significantly in one serum sample taken four days and one taken 20 days after infection (P<0.01) and there was a significantly lower relative slope for one serum sample 20 days after infection (P<0.05). Maximal relative aggregation responses to thrombin were significantly decreased together with their relative slopes in serum samples from two of four dogs four days after infection (P<0.05). The results suggest that platelet dysfunction may occur in the acute stage of canine ehrlichiosis, and may be a contributing factor to the tendency to bleed commonly observed in this disease. Antiplatelet antibodies directed against platelet glycoproteins may play a role in the inhibition of platelet aggregation.