Evaluation of an enzyme immunoassay and immunodiffusion for detection of anti-Histoplasma antibodies in serum from cats and dogs.

Abstract

BACKGROUND: Histoplasma antigen and anti-Histoplasma antibody detection are used to support the diagnosis of histoplasmosis. There is a paucity of published data on antibody assays. OBJECTIVES: Our primary hypothesis was that anti-Histoplasma immunoglobulin G (IgG) antibody detection using enzyme immunoassay (EIA) will be more sensitive as compared to immunodiffusion (ID). ANIMALS: Thirty-seven cats and 22 dogs with proven or probable histoplasmosis; 157 negative control animals. METHODS: Residual stored sera were tested for anti-Histoplasma antibodies using EIA and ID. Results of urine antigen EIA were reviewed retrospectively. Diagnostic sensitivity was calculated for all three assays and compared between immunoglobulin G (IgG) EIA and ID. The diagnostic sensitivity of urine antigen EIA and IgG EIA, interpreted in parallel, was reported. RESULTS: Sensitivity of IgG EIA was 30/37 (81.1%; 95% confidence interval [CI], 68.5%-93.4%) in cats and 17/22 (77.3%; 95% CI, 59.8%-94.8%) in dogs. Diagnostic sensitivity of ID was 0/37 (0%; 95% CI, 0%-9.5%) in cats and 3/22 (13.6%; 95% CI, 0%-28.0%) in dogs. Immunoglobulin G EIA was positive in all animals (2 cats and 2 dogs) with histoplasmosis but without detectable antigen in urine. Diagnostic specificity of IgG EIA was 18/19 (94.7%; 95% CI, 74.0%-99.9%) in cats and 128/138 (92.8%; 95% CI, 87.1%-96.5%) in dogs. CONCLUSION AND CLINICAL IMPORTANCE: Antibody detection by EIA can be used to support the diagnosis of histoplasmosis in cats and dogs. Immunodiffusion has an unacceptably low diagnostic sensitivity and is not recommended.