Pulmonary Dirofilariasis

Figure 1: Adult worm inside dog heart.  4

Canine heartworm is a common parasite of dogs all around the world.  It is also responsible for a rare zoonotic infection in humans.  Unlike an animal infection, where the adult worm resides in the right ventricle of the heart or pulmonary artery for many years, a worm in a human host is less likely to survive for a long period, and is carried to the lung where it produces a solitary nodule.  This is a result of a thrombus forming around the worm and the subsequent granulomatous and fibrotic reactions to the antigens released by the degenerating worm in the tissues.  Heartworm is caused by the agent Dirofilaria immitis, with the taxonomic classification:

Phylum: Nematoda

Class: Chromadorea

Order: Spirurida

Suborder: Spirurina

Superfamily: Filarioidea

Family: Onchocercidae

Created by:

Kat Hoffman, Class of 2007, kjo@stanford.edu

Stanford University

Parasites & Pestilence: Infectious Public Health Challenges

Prof. D. Scott Smith, ssmith@stanford.edu