Clinical Presentation in Humans
    Human pulmonary dirofilariasis develops when the larval form of D. immitis dies, embolizes to the lung, and lodges in a small pulmonary artery branch.  HPD is characteristically manifested by a solitary pulmonary nodule, which is easily confused with malignancy.  The majority of patients (about 60%) with pulmonary dirofilariasis are asymptomatic.  Symptomatic patients commonly experience chest discomfort, cough, fever, chills, malaise, hemoptysis, and eosinophilia.  Chest x-ray examination will usually reveal a noncalcified, well-circumscribed, pulmonary nodule (coin lesion) in the periphery of the lungs.  The nodule will usually be less than 4 centimeters in diameter, although it may be as large as 4.5 centimeters in diameter.  Although there is great morphologic variation seen, the lesion is generally characterized by a central necrotic area surrounded by a granulomatous inflammation and a fibrous wall.  Dead or dying worms at different stages of necrosis and calcification are found in the lesion.  The lesion is often marked by an inflammatory reaction, with abundant histiocytes, eosinophils, lymphocytes, and plasma cells infiltrating the infected area.

Figure 1: Chest x-ray showing a pulmonary "coin" lesion caused by Dirofilaria immitis infection in
 an adult man.  Image from

Figure 2: CT scan of a solitary, noncalcified, left upper lobe pulmonary nodule caused by
infection by D. immitis.  Image from April, 2001, volume of Chest.

    Subcutaneous dirofilariasis manifests itself clinically by a 1 to 3 cm nodule anywhere in the body, with common sites of infection including: subcutaneous tissue, pectoral muscle, genitals, breast tissue, urinary bladder, portacaval shunt, peritoneal cavity, ocular cavity, and eyelids.  The clinical manifestations of the infection and morphological appearance of the lesions are similar in infecton by all species of subcutaneous Dirofilaria.  It is rare for an infected patient to present with multiple nodules.
    In the first several months of infection, the nodule is usually painless and does not give rise to inflammation.  It may also disappear and reappear in a new location.  As the infection progresses and the nodule grows, however, pain and inflammation may result.  Other symptoms may include: edemas, arthritis, subcutaneous swellings, and eosinophilia.  Abdominal wall infection by D. repens in a Kuwaiti man resulted in symptoms of abdominal swelling and pain, as well as detection of an apparent bulge and mild redness in the area of infection (Hira, et al).  When the parasite infects the subconjuctiva in the eye, intense irritation, or conjunctivitis may result.  In a case of eyelid infection by D. repens in a Spanish woman, subcutaneous migratory movement of the worm was detected upon close examination (Fuentes, et al).
    Surgical removal of the worm usually recovers the organism within the nodule itself at various stages of degeneration.  In the majority of extrapulmonary dirofilariasis cases, the recovered worm is in immature (larval) stages.  In more rare cases, adult worms of small size and incomplete sexual maturation are recovered.

Figure 3: Abdominal wall nodule showing immature female Dirofilaria immitis,
surrounded by necrotizing granulomatous and eosinophilic inflammation.

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