Pathologic findings in dogs with shock induced by intravenous administration of heartworm extract.

OBJECTIVE

To examine pathologic findings in dogs with shock induced by IV administration of heartworm (HW) extract.

ANIMALS: 22 mixed-breed adult dogs.

PROCEDURES: Heartworm extract was administered IV, and pathologic changes in dogs that died or were euthanatized at 24 hours were examined.

RESULTS

The most severe lesions observed during initial collapse were centralobular congestion in the liver, hemorrhage and edema in the gallbladder wall, and congestion and hemorrhage in mucous membranes of the gastrointestinal tract. These findings disappeared with recovery from collapse. Hyalinization of venous walls of the liver and cardiac muscle were observed in dogs that died during initial collapse. Focal coagulation necrosis in hepatic cells was seen in dogs that were euthanatized at 24 hours. One dog with profuse bloody diarrhea that died during secondary collapse had severe hemorrhage in mucous membranes of the large intestine.

CONCLUSION

Heartworm extract appeared to contain some substances constricting hepatosplanchnic vessels and some toxic substances that injured the smooth muscle of venous walls, cardiac muscle, and hepatic cells directly or indirectly.

CLINICAL RELEVANCE: The shock-inducing substances in HW extract may have an important role in the pathophysiologic mechanism of HW disease, and investigation of them may contribute to prevention of the shock reaction attributable to microfilaricide and adulticide use.