Paragonimiasis may present with a range of clinical fi ndings. Th e majority of patients infected will have few clinical symptoms. Th e most common fi nding may be a nonspecifi c elevation of the peripheral eosinophil count. In one report, 80% of patients with paragonimiasis had eosinophilia detected on peripheral blood smear.
More severe disease is associated with higher organism burden. Symptomatic infection is a manifestation of infl ammatory, oft en hemorrhagic lesions produced as the organisms migrate from the bowel, traverse the peritoneal cavity and lodge in the lungs and/or other organs. Th e local infl ammatory reaction includes eosinophilic
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exudates and, in some cases, a granulomatous reaction to the eggs. Examination of expectorated sputum under light microscopy should be obtained for the presence of the brown, operculate eggs as well as for eosinophils and Charcot-Leyden crystals. When secretions are swallowed, eggs may also be found in the stool of infected patients. Both sputum and stool should be sent for microscopic evaluation when pulmonary paragonimiasis is suspected.
Hemoptysis and cough are the most common clinical symptoms of pulmonary paragonimiasis. In countries where both paragonimiasis and tuberculosis are
Figure 15.1. Life Cycle of Paragonimus westermani. Reproduced from: Nappi AJ, Vass E, eds. Parasites of Medical Importance. Austin: Landes Bioscience, 2002:47.
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Paragonimiasis
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endemic, it is not uncommon for patients to be treated empirically for tubercu- losis based on their similar clinical presentations. Th e parasitic diagnosis is oft en obtained aft er a more thorough inspection of the sputum and/or the stools are sent for examination. In addition to mimicking tuberculosis, pulmonary paragoni- miasis can be mistaken for bronchiectasis or other respiratory diseases that may present with increased sputum production and/or pleuritic chest pain. A careful epidemiologic history and high clinical suspicion for diagnosis are necessary when considering this disease in a patient with pulmonary disease.
Examination of pleural fl uid may also demonstrate eosinophilia and the eggs on cytologic examination. Other pleural fl uid indicators mimic bacterial infection with low pH, low glucose (<10 mg/dl) and elevated protein and lactate dehy- drogenase, suggesting an exudative process. Th e parasite and the eggs have been identifi ed on microscopic examination of bronchoalveolar lavage and fi ne needle aspiration of pulmonary lesions. In rare cases, the adult worms may be seen in the sputum or expectorated with coughing aft er the initiation of therapy.
Th e organism’s migration through the peritoneal cavity may lead to intra- abdominal seeding. Clinical cases of hepatic, omental and retroperitoneal collec- tions have been described. Eggs reaching the circulation or fl uke migrations outside the pulmonary cavity may direct disease to distal sites, leading to ectopic foci of infection. Th e immature fl ukes of P. skrjabini, native to China, have been associ- ated with cutaneous involvement known as trematode larval migrans. Unlike the other species of Paragonimus, this particular species is associated with migratory subcutaneous nodules and, only rarely, pulmonary disease.
Worldwide, other focal skin infections have been reported, as well as in- traocular, pericardial or brain involvement with P. westermani and a variety of other Paragonimus species. Cerebral involvement is one of the most common extrapulmonary sites. When aff ecting the brain, paragonimiasis may present as a mass lesion with or without seizure, chronic meningeal irritation or acute meningitis; it is associated with a high mortality due to the higher incidence of intracranial hemorrhage.
Th e diagnosis of paragonimiasis may be aided by radiologic imaging; however the fi ndings are generally nonspecifi c. In a retrospective review of over 70 patients with pleuropulmonary paragonimiasis, chest radiographs demonstrated pleural lesions in over half of the cases reviewed, with less than 20% showing evidence of pleural eff usion. Nonspecifi c fi ndings of the parenchymal lung disease on radiographs include air space consolidation, cystic changes and peripheral linear densities. Th e radiographically opaque linear densities have been attributed to the parasite’s migration tracks through the tissues.
Computed tomography (CT) has been used to aid in the diagnosis of pulmo- nary and extrapulmonary paragonimiasis. CT is more sensitive in demonstrating small pleural eff usions and better depicts the mass lesions seen on radiographs. Masses usually consist of one or more peripheral, irregularly shaped densities which calcify with time. Characteristically, the mass lesions may display either a low at- tenuation signal at their center or show evidence of an air-fl uid level, associated with ring-like enhancement at the edges. In setting of pulmonary paragonimiasis, these lesions have been described as “worm cysts.” Recently, Kuroki et al evaluated eight patients with high-resolution CT and were better able to demonstrate bronchial
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thickening and ground-glass opacities in association with the usual CT fi ndings of pulmonary paragonimiasis.
Radiologic imaging studies serve as an important adjunct to the diagnosis of paragonimiasis, but defi nitive diagnostic evaluation today requires microbiologic and, increasingly, serologic methods. It may take up to 3 weeks for fl ukes to mature and produce eggs visible for microscopic diagnosis. To augment microscopic ex- amination in cases where infection may be early or those samples diffi cult to access (extrapulmonary disease), immunologic tests have been developed.
Th e diagnosis of patients with early pulmonary disease or those with extra- pulmonary disease has been improved with the development of serologic testing. While a simple intradermal test has been developed, the cutaneous reaction cannot accurately distinguish between active or past infection despite good sensitivity. Enzyme linked immunosorbent assays (ELISA) with greater specifi city and sensi- tivity for infection have been developed, including an ELISA using the parasite’s excretory-secretory antigens. PCR assays are under development and are not yet commercially available; however these assays hold the promise of being able to diff erentiate among the various Paragonimus species in addition to diagnosing infection.