ID05 - Evaluation of Anti-Histoplasma Antibody Detection via Enzyme Immunoassay or Immunodiffusion in Cats and Dogs

Abstract: Background – Anti-Histoplasma antibody detection by enzyme immunoassay (EIA) or immunodiffusion (ID) is used to support the diagnosis of histoplasmosis in cats and dogs. There is a paucity of published diagnostic performance data.

Objectives – The primary objective was to describe the performance of IgG EIA and ID for anti-Histoplasma antibody detection in cats and dogs. A secondary aim was to describe the clinical utility of antibody detection when combined with antigen detection.

Animals – 51 animals with pathology proven histoplasmosis and 160 animals without histoplasmosis.

Methods – This is a retrospective cohort study. Results of Histoplasma antigen EIA at the time of diagnosis was included in extracted data. Stored serum samples were tested for anti-Histoplasma antibodies by EIA and ID. Diagnostic sensitivity was calculated.

Results – Diagnostic sensitivity of IgG EIA was 24/30 (80.0%) in cats and 17/21 (81.0%) in dogs. Diagnostic sensitivity of ID was 0/30 (0%) in cats and 3/21 (14.3%) in dogs. Diagnostic sensitivity of Histoplasma antigen in urine was 28/30 (93.3%) in cats and 19/21 (90.5%) in dogs. When interpreted in parallel, combined diagnostic sensitivity of antigen EIA and IgG EIA was 51/51 (100%) in both species. In animals not diagnosed with histoplasmosis, anti-Histoplasma IgG antibodies were detected in 1/21 (4.8%) of cats and 10/138 (7.2%) of dogs.

Conclusions and Clinical Importance – Immunodiffusion is not recommended for anti-Histoplasma antibody detection in cats and dogs. Anti-Histoplasma antibody detection by EIA should be considered with suspected histoplasmosis but no detectable Histoplasma antigen in urine.