Three types of immunotherapics against pythiosis insidiosi developed and evaluated.

Pythiosis is a granulomatous disease of horses, cattle, dogs, cats and humans identified in tropical and subtropical areas and caused by Pythium insidiosum, a zoosporic fungus. Experimental models of pythiosis in naturally infected species have not yet been reported but, rabbits may be inoculated with zoospores as an experimental model for studying the disease. The present study evaluates the efficacy of three different of immunotherapics in the rabbit model. Approximately 17500 zoospores of oomycete P. insidiosum (CBS 101555 strain) were inoculated in each animal to generate the disease. Immunotherapics were produced from vortexed or sonicated cultures of the same strain. Four groups of five animals were employed: group 1, placebo; group 2, sonicated immunotherapic; group 3, mixed immunotherapic; and group 4, vortexed immunotherapic. All rabbits were inoculated with viable zoospores one month before administration of the immunotherapics. Eight doses of immunotherapic or placebo were used in each animal with a 14 day interval between injections. Rabbits receiving the vortexed immunotherapic were most effectively protected (P<0.05), showing a decrease in the area of coastal nodules due to Pythiosis insidiosum by 71.8% after 26 weeks of evaluation. Moreover, two animals in this group showed complete remission of the infection at the end of the 26 weeks. In contrast to these findings, rabbits given the sonicated immunotherapic did not show any protection and had an increase of 211.8% in the size of lesions. This failure of sonicated immunotherapic may reflect denaturation of protective antigens due to the sonication method.