[Dirofilaria immitis] [D. repens] [D. tenuis] [D. ursi]
Zoonotic filarid nematodes in the genus Dirofilaria. The normal hosts for Dirofilaria spp. in nature are usually carnivores. The most commonly seen species in human patients are D. repens, D. tenuis, and D. immitis (the dog heartworm). Humans have also been infected with D. ursi, D. subdermata, and D. striata.
Dirofilaria immitis is cosmopolitan in dogs. Dirofilaria repens infects dogs and cats in the Old World, while D. tenuis infects raccoons in North America. Dirofilaria ursi and D. subdermata are also North American, infecting bears and porcupines, respectively. Dirofilaria striata is a parasite of wild felids in North, Central, and South America.
Dirofilaria immitis causes pulmonary disease in humans. The parasite cannot develop in the human host and larvae that migrate to the heart usually die. Dead worms produce infarcts when they lodge in pulmonary vessels; these infarcts are usually referred to as "coin lesions". Following embolization, patients may present with chest pain, cough, fever, chill, malaise, and hemoptysis. There is often a mild eosinophilia. Other species of Dirofilaria usually manifest as subcutaneous nodules. These nodules are usually, tender, painful, and may be migratory. Adults of D. repens and D. tenuis are often found in the subconjunctiva.
Figure A: Cross-section of Dirofilaria sp. from a subcutaneous nodule, stained with hematoxylin and eosin (H&E). Morphologic features visible in this image include tall, prominent muscle cells (MU), coiled vagina (VG), coiled intestine (IN), lateral chords (LC), and prominent internal lateral ridges (IR). Image courtesy of Drs. Dirk Elston and Paul Bourbeau.
Figure B: Cross-sections of Dirofilaria spp. from a subcutaneous scalp nodule, stained with H&E. Image courtesy of the Department of Dermatopathology, University of Michigan, Ann Arbor, MI.
Figure C: Cross-sections of Dirofilaria sp. from a subcutaneous nodule above the right breast of a female patient who traveled to several western European countries, stained with H&E. Image taken at 100x magnification. Image courtesy of Dr. Truus Derks.
Figure D: Higher magnification of the same specimen as Figure C, taken at 400x magnification. Note the presence of lateral chords (blue arrows) and internal lateral ridge (black arrow).
Figure E: Dirofilaria sp. (suspect D. tenuis) removed from the eye of a patient.
Figure F: Close-up of the specimen in Figure E showing the cuticular ridging. A uterine tube can also be seen through the cuticle.
Dirofilaria immitis is usually diagnosed by the finding of coin lesions on chest roentgenograms. The species that produce subcutaneous nodules are diagnosed by the finding of adult worms in biopsy specimens of the nodules. The morphologic features of the cuticle, musculature, and lateral chords are important criteria for identifying Dirofilaria. Worms removed from the eye are usually diagnosed by external features of the cuticle; worms may also be processed by routine histologic methods to study the internal structures. There are currently no serologic or molecular methods available for diagnosing human dirofilariasis in the U.S.
The definitive treatment of Dirofilaria infection in humans is surgical removal of lung granulomas and subcutaneous nodules; this treatment is also curative. In many cases, no drug treatment is necessary.
DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.
- Page last reviewed: May 3, 2016
- Page last updated: May 3, 2016
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