Semiquantitative test for Dirofilaria immitis as a predictor of thromboembolic complications associated with heartworm treatment in dogs

Clarence A. Rawlings From the Departments of Small Animal Medicine and of Physiology and Pharmacology (Rawlings), Anatomy and Radiology (Lewis), and Pathology (Duncan), College of Veterinary Medicine, University of Georgia, Athens, GA 30602, and the IDEXX Corp, Portland, ME 04101 (Tonelli).

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Quentin Tonelli From the Departments of Small Animal Medicine and of Physiology and Pharmacology (Rawlings), Anatomy and Radiology (Lewis), and Pathology (Duncan), College of Veterinary Medicine, University of Georgia, Athens, GA 30602, and the IDEXX Corp, Portland, ME 04101 (Tonelli).

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Robert E. Lewis From the Departments of Small Animal Medicine and of Physiology and Pharmacology (Rawlings), Anatomy and Radiology (Lewis), and Pathology (Duncan), College of Veterinary Medicine, University of Georgia, Athens, GA 30602, and the IDEXX Corp, Portland, ME 04101 (Tonelli).

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J. Robert Duncan From the Departments of Small Animal Medicine and of Physiology and Pharmacology (Rawlings), Anatomy and Radiology (Lewis), and Pathology (Duncan), College of Veterinary Medicine, University of Georgia, Athens, GA 30602, and the IDEXX Corp, Portland, ME 04101 (Tonelli).

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Summary

A semiquantitative heartworm test of antigen concentration was evaluated as a predictor of thromboembolism after adulticide treatment. Seventeen dogs with naturally acquired infections of Dirofilaria immitis (heartworms) were studied before and after thiacetarsamide treatment, using physical examinations, arterial blood gas analyses, thoracic radiography, and pulmonary hemodynamic and arteriographic tests. Eight dogs were considered to have a low burden of heartworms and 9 had a high burden. Dogs with a high worm burden had more severe pulmonary thromboembolism with pulmonary hypertension, dilated pulmonary arteries, flow obstruction of the caudal pulmonary arteries, and parenchymal lesions in the caudal lung lobes. Dogs with a low worm burden had minimal changes. Within each group of dogs, the severity of thromboembolism was less in some dogs in which all heartworms were not killed. Six of the 9 dogs with a high burden of heartworms had surviving heartworms, and 1 of these dogs had 38 live heartworms. Only 4 of the 8 dogs with a low worm burden had complete heartworm mortality, but only 1 dog had more than 3 surviving heartworms. We concluded that dogs with a high worm burden were more likely to have pulmonary thromboembolism after thiacetarsamide treatment and that dogs with a low worm burden were more likely to have minimal changes. A semiquantitative heartworm test of antigen concentration is recommended as part of the pretreatment evaluation of dogs infected with heartworms.

Summary

A semiquantitative heartworm test of antigen concentration was evaluated as a predictor of thromboembolism after adulticide treatment. Seventeen dogs with naturally acquired infections of Dirofilaria immitis (heartworms) were studied before and after thiacetarsamide treatment, using physical examinations, arterial blood gas analyses, thoracic radiography, and pulmonary hemodynamic and arteriographic tests. Eight dogs were considered to have a low burden of heartworms and 9 had a high burden. Dogs with a high worm burden had more severe pulmonary thromboembolism with pulmonary hypertension, dilated pulmonary arteries, flow obstruction of the caudal pulmonary arteries, and parenchymal lesions in the caudal lung lobes. Dogs with a low worm burden had minimal changes. Within each group of dogs, the severity of thromboembolism was less in some dogs in which all heartworms were not killed. Six of the 9 dogs with a high burden of heartworms had surviving heartworms, and 1 of these dogs had 38 live heartworms. Only 4 of the 8 dogs with a low worm burden had complete heartworm mortality, but only 1 dog had more than 3 surviving heartworms. We concluded that dogs with a high worm burden were more likely to have pulmonary thromboembolism after thiacetarsamide treatment and that dogs with a low worm burden were more likely to have minimal changes. A semiquantitative heartworm test of antigen concentration is recommended as part of the pretreatment evaluation of dogs infected with heartworms.

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