| Summary: | Pythium insidiosum is an aquatic oomycete that causes invasive, progressive granulomatous lesions of the skin in dogs, horses, and cats, and of the gastrointestinal tract in dogs. Quantitation of anti-P. insidiosum IgG antibodies can be used in dogs to both confirm a suspected diagnosis and to monitor response to therapy. Recently, an immunotherapeutic product (IP) has been marketed for the treatment of pythiosis in dogs, horses, and people. The aim of this study was to evaluate the effect of administration of this product on anti-P. insidiosum IgG concentrations in dogs. The IP was administered to seven, healthy hound mixes on days zero, seven and 21. Serum was collected on days zero, seven, 14, 21, 28, 35, 42, 49, and 56. Anti-P. insidiosum antibody concentrations were measured using a previously-described ELISA that utilizes a soluble mycelial-based antigen, with results reported as percent positivity (PP) in comparison to a strong positive control serum. Prior to immunotherapy administration, average PP was 7.45% +/- 3.02%. Following immunotherapy administration, there was no significant change in anti-P. insidiosum antibody concentrations, with PP values in all dogs remaining within the range expected for healthy dogs (3% - 15%) for the entire study period. In conclusion, the IP did not produce a significant change in anti-P. insidiosum IgG concentrations when administered to healthy dogs using the protocol suggested by the manufacturers. Further investigation will be required to determine whether a similar effect is observed in naturally infected dogs.
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