Caval syndrome in a Dirofilaria immitis-infected dog treated with dichlorvos.

In the dog of this report, lesions found were compatible with death attributable to acute circulatory collapse induced by caval syndrome and compounded by microfilarial death. Hepatic centrilobular hemorrhage and necrosis were suggestive of circulatory collapse, renal hemosiderosis was suggestive of disseminated intravascular coagulopathy, and multifocal subacute hepatic inflammation associated with microfilariae was similar to lesions attributed to microfilarial death. Treatment with dichlorvos may have precipitated these events. Previous descriptions of dichlorvos toxicity in microfilaremic dogs have suggested that death is attributable to shock, but pathogenic mechanisms have not been established. Although generalizations from a single case must be made with caution, lesions in this dog suggest that toxic effects may be mediated through effects on adult and larval heartworms.