A minireview of the pathogenesis of acute leptospirosis.

Hemorrhagic diathesis is one of the most striking manifestations in acute leptospirosis. Hemorrhages are seen in infections due to Leptospira icterohaemorrhagiae as well as in those caused by Leptospira pomona. Thrombocytopenia is a constant feature and its finding can be useful for the diagnosis. Attempts to demonstrate the presence of a toxin in leptospires were unsuccessful. A few years ago, a syndrome of disseminated intravascular coagulation was associated with the physiopathogenesis of experimental leptospirosis with L. icterohaemorrhagiae. More recently, this syndrome was identified in cases of human leptospirosis and in hamsters infected with L. pomona. It appears now that other spirochetal infections (borreliosis) have a similar pathogenesis. Nonetheless, many points are still unclear: the primary cause of disseminated intravascular coagulation is unknown, as well as the virulence factors of spirochetes. Some points favor the presence of a toxic factor in leptospires: vascular damage that occurs in the absence of leptospires in damaged areas and the fact that antibiotic therapy is ineffective unless treatment is initiated early in the disease.