Case report: Paragonimiasis westermani with seroconversion from immunoglobulin (Ig) m to IgG antibody with the clinical course.

A 66-year-old man visited our hospital with primary complaint of cough. Chest roentgenogram showed slight pleural effusion and pneumothorax in the left lung. Eosinophilia (22.8%) was also found in his peripheral blood. Multiple-dot enzyme-linked immunosorbent assay (dot-ELISA) for the detection of parasite-specific immunoglobulin (Ig) G antibody was used to screen his serum against various parasitic diseases, but no significant binding was observed with any of the 12 parasite antigens examined, including those of Paragonimus westermani and P. miyazakii. Although he seemed to have been spontaneously cured without treatment, a nodular shadow appeared in the right upper medial lung field on the chest roentgenogram 6 months later. This time, his serum was positive for anti-P. westermani IgG antibody by the same method. A reexamination of the first and second admission serum samples for parasite-specific IgM and IgG antibodies revealed significant level of IgM antibody in the serum of the first admission, which had decreased at the time of the second admission. Conversely, the level of IgG antibody, which was low at the first admission, became dominant in the second admission serum 6 months later. These results clearly show that although the dot-ELISA to detect IgG antibody is generally useful for screening and detecting paragonimiasis, detection of IgM antibody seems to be a useful aid and should also be included in immunoserological diagnosis, especially if the patient is considered to be in the early stage of infection.