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*WBC = white blood cells, Eos = eosinophils.

*WBC = white blood cells, Eos = eosinophils.

Fig. 17.5 Chest roentgenogram of patient infected with Paragonimus with a ring cyst at the left heart border. Reproduced by courtesy of Dr Richard Johnson, University of Washington Medical Center, Seattle, USA

Intradermal Test

An intradermal test with an extract of Paragonimus antigens measures an immediate wheal reaction after 15 minutes (Sadun and Buck, 1960). The sensitivity range is in the 82-100%, with a specificity of 97% in one series (Table 17.9) (Chang et al, 1988; Sadun and Buck, 1960; Shim et al., 1991). Although this test has good performance characteristics, it is not widely available, is not standardized, has some cross-reactivity with Clonorchis antigens and does not differentiate between current and past infections. It is predominantly used for epidemiologic studies.

Sputum and Stool Analysis

With the secretion of eggs by the adult worms in the lungs, analysis of the sputa for ova provides the most direct method for detecting infection. Sensitivity for submission of one sample is limited, with a range of 37-57% (Table 17.9). Submission of serial samples improves the sensitivity to as high as 89% with greater than six samples. The specificity of these tests is presumed to be high, although it has not been reported. Less specific tests include analysis for Charcot-Leyden crystals and eosinophils, which are both present in the majority of cases. The absence of these findings is helpful in ruling out Paragonimus.

Since the eggs are often swallowed after expulsion from the lungs, some cases can be diagnosed by detecting ova in the stool (Table 17.9). Even though the sensitivity is low, occasional patients will have no ova in their sputum and be diagnosed through stool studies.

Serologic

Excellent serologic tests are available to complement sputum and stool studies. The most widely used test in the past has been complement fixation, which has a sensitivity of around 96% (Table 17.9). More recently, ELISA tests have become available, which are more practical for widespread use (Johnson and Johnson, 1983; Pariyanonda et al., 1990). The CDC currently utilizes the immunoblot, which has a sensitivity and specificity of 96% and 99%, respectively (Slemenda et al., 1988). An antigen detection test is also available, with a sensitivity of 100% and a specificity of >99%, but is not currently in widespread use (Zhang et al., 1993).

Molecular Techniques

DNA-based techniques have not yet had a role in the clinical diagnosis of paragonimiasis.

Overall, diagnosis of paragonimiasis is usually accomplished by detection of eggs in sputum or stool, with or without the assistance of serologic studies.

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