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[Brugia malayi] [Brugia timori] [Dirofilaria spp.] [Loa loa] [Mansonella ozzardi] [Mansonella perstans] [Mansonella streptocerca] [Onchocerca volvulus] [Wuchereria bancrofti]

The genus Dirofilaria consists of many species that infect a wide range of hosts worldwide, including carnivores, rodents and primates.  Humans are incidental hosts for several of these; the most frequent include D. immitis (dog heartworm), D. tenuis (raccoons) and D. repens (dogs).  The worms usually die before completing their development in the human host, but tend to follow the same migratory pathway as in the natural definitive host; D. tenuis and D. repens most often remain in the subcutaneous tissue where the dying worms produce a localized granulomatous nodule, or, in the case of D. immitis, pulmonary infarcts and/or nodules often appearing as coin lesions on X-ray.  Humans acquire Dirofilaria when bitten by mosquitoes (rarely black flies), the arthropod vector and intermediate host.

A	B

A: Cross-sections 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.
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.

C	D

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.
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).

E	F

E: Dirofilaria sp. (suspect D. tenuis) removed from the eye of a patient.
F: Close-up of the specimen in Figure E showing the cuticular ridging.  A uterine tube can also be seen through the cuticle.