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Dirofilaria immitis

Reviewer: Elliot Weisenberg, M.D. (see Reviewers page)
Revised: 7 May 2014, last major update September 2011
Copyright: (c) 2003-2012, PathologyOutlines.com, Inc.

Clinical features

● Dog heartworm; may infect humans as secondary end-stage host, particularly in southern coastal states in US
● Adult worms die in right ventricle, embolize in pulmonary arterial circulation
● Embolization of dead worms may be clinically silent or cause chest pain, fever, chills, hemoptysis or blood eosinophilia
● Evokes necrotizing granulomatous response with vasculitis in lung tissue
● Rarely see dead worms
● Usually self-limited in humans, but may cause lung infarct
● Usually diagnosed after resection of a nodule to exclude malignancy
Chest Xray: solitary peripheral pulmonary nodule or coin lesion (Int J Immunopathol Pharmacol 2010;23:345)

Case Reports

● 15 year old girl with solitary pulmonary nodule (Arch Pathol Lab Med 2002;126:227)

Micro description

● Rounded infarct with coagulative necrosis, well demarcated from surrounding normal lung by epithelioid histiocytes and fibrous connective tissue
● Focal calcifications and lymphoid aggregates
● Necrotic nematode has homogenous cuticle without external ridges
● Longitudinal muscle layer just internal to cuticle and internal cuticular ridges

Micro images


Pulmonary embolization, contributed by Dr. Vladimir Zaitsev, Russia

H&E and Movat stain

End of Lung-nontumor > Infections > Dirofilaria immitis

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