Presentation in Humans
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.
Human Pulmonary Dirofilariasis
Figure 1: Chest x-ray showing a
pulmonary "coin" lesion caused by Dirofilaria immitis infection
an adult man. Image from emedicine.com:
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.
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.
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,
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,
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
Figure 3: Abdominal wall nodule
showing immature female Dirofilaria immitis,
surrounded by necrotizing granulomatous
and eosinophilic inflammation.
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