Persistence of cryptococcal antigenemia in an infected dog and uninfected rabbits

A case of cryptococcosis in a dog is reported. The titers of polysaccharide antigen in sera were monitored by latex agglutination (LA) tests during and after treatment with antifungal therapy. Although the LA titers decreased in response to therapy, it took about 3.5 years to achieve a negative LA test. To model the persistence of cryptococcal polysaccharides, we examined the clearance of antigen from the blood of rabbits injected with sterile, cryptococcal capsular polysaccharide isolated from culture supernatant. The distribution half-lives were between 2.6 and 3.9 days and the elimination half-lives were between 10.4 and 39 days. These results suggest that polysaccharide antigen may be stored in tissues. However, we think that slow clearance of antigen cannot explain the extraordinarily slow clearance found in this dog, and that prolonged survival of Cryptococcus neoformans is a more plausible explanation.