[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.
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.
DPDx is an education resource designed for health professionals and laboratory scientists. For an overview including prevention and control visit www.cdc.gov/parasites/.