Immunodiffusion test for diagnosis and monitoring of human pythiosis insidiosi.

To facilitate the laboratory diagnosis of human cases of pythiosis insidiosi, an immunological test was evaluated. A soluble antigen was prepared from a human isolate of Pythium insidiosum, an aquatic, thermotolerant oomycete that causes infections in cattle, dogs, horses, and humans. Sera from seven proven cases of disseminated human pythiosis insidiosi were tested in an immunodiffusion test along with appropriate control sera from patients with a variety of actinomycotic, bacterial, and mycotic diseases as well as sera from uninfected individuals. Titers ranged from 1:1 to 1:32 in the seven serum samples from the disseminated cases of pythiosis insidiosi of varying severity. The heterologous sera gave negative reactions. The rapidity and specificity of the immunodiffusion test makes it a useful diagnostic tool for the serodiagnosis of P. insidiosum infections.