[Mycological and serological diagnosis of cryptococcosis]

Methods for the diagnosis of cryptococcosis have been established, including serotyping and serodiagnosis. Slide agglutination tests with factor sera, the phenol oxidase test, and the growth test at 37C are used for rapid identification of Cryptococcus neoformans. We identified 140 strains and found that 86, 10, and 4% of the isolates were serotypes A, D, and A-D, respectively. Twelve of 14 serotype D strains were isolated from cutaneous cryptococcosis. The most reliable method of serodiagnosis is the latex agglutination (LA) test for detection of polysaccharide antigen combined with protease pretreatment. The LA test is also used for prognosis. The clearance of cryptococcal polysaccharide antigen often takes a few years after treatment. To model the persistence of cryptococcal polysaccharides, we examined the clearance of antigen from the blood of rabbits injected with polysaccharide. The distribution and elimination half-lives of the antigen suggest the prolonged survival of C. neoformans. Recently, the number of cases of C. albidus and C. laurentii has been increasing. The antigenic pattern and the sensitivity of C. albidus in the LA test are the same as that of C. neoformans serotype A. In contrast, C. laurentii does not react with factor sera for C. neoformans and the reactivity with sensitized latex is extremely low. These results were supported by the chemical structures of polysaccharides from these species. We should consider non-neoformans cases in both the identification of isolates and in serodiagnosis.