Development and Evaluation of an ELISA for the Quantitation of Anti‐ Lagenidium giganteum forma caninum Antibodies in Dogs

Background Lagenidium giganteum forma caninum infection causes severe cutaneous and disseminated disease in dogs. Currently, diagnosis requires culture and rRNA gene sequencing. Objective To develop and evaluate an ELISA for quantitation of anti‐ L. giganteum f. caninum IgG in canine serum. Animals Sera were evaluated from 22 dogs infected with L. giganteum f. caninum , 12 dogs infected with Paralagenidium karlingii , 18 dogs infected with Pythium insidiosum , 26 dogs with nonoomycotic fungal infections or other cutaneous or systemic diseases, and 10 healthy dogs. Methods Antigen was prepared from a soluble mycelial extract of L. giganteum f. caninum . Optimal antigen and antibody concentrations were determined by checkerboard titration. Results were expressed as percent positivity ( PP ) relative to a strongly positive control serum. Results Medians and ranges for PP for each group were: L. giganteum f. caninum (73.9%, 27.9–108.9%), P. karlingii (55.0%, 21.0–90.6%), P. insidiosum (31.3%, 15.8–87.5%), nonoomycotic fungal infection or other cutaneous or systemic diseases (19.2%, 3.2–61.0%), and healthy dogs (9.9%, 7.6–24.6%). Using a PP cutoff value of 40%, sensitivity and specificity (with 95% CI ) of the ELISA for detecting L. giganteum f. caninum infection in clinically affected dogs were 90.9% (72.2–97.5%) and 73.2% (60.4–83.0%), respectively. Specificity in dogs infected with P. karlingii was 41.7% (19.3–68.1%) and with P. insidiosum was 66.7% (43.8–83.7%). Conclusions and Clinical Importance Quantitation of anti‐ L. giganteum f. caninum antibodies for detection of this infection in dogs has moderately high sensitivity but poor specificity, the latter because of substantial cross‐reactivity with anti‐ P. karlingii and anti‐ P. insidiosum antibodies.