TRP36-ELISA for E. canis detection: Concordance with TaqMan real-time PCR and point-of-care testing

<i>Ehrlichia canis</i>, a widely distributed tick-borne pathogen, requires prompt and accurate diagnosis for effective management. Real-time PCR serves as the reference standard for diagnosing <i>E. canis</i> infection, whereas serological tests are crucial for detecting antibody responses indicative of infection or post-exposure status. Early detection during the acute phase of the disease is essential for optimal treatment and recovery. <i>E. canis</i> Tandem Repeat Protein 36 (TRP36) elicits early acute phase responses. We developed an enzyme-linked immunosorbent assay (ELISA) using recombinant TRP36 to detect IgM and IgG antibodies against <i>E. canis</i>. We assessed the diagnostic agreement, sensitivity, and specificity of the rTRP36-ELISA and a commercial test kit (SNAP 4Dx Plus Test) with TaqMan Real-time PCR (qPCR) using the NCSS 2023 program version 23.0.1. Leftover serum samples from 32 dogs at the Veterinary Teaching Hospital were randomly selected and examined for <i>E. canis</i> infection using qPCR, rTRP36-ELISA, and SNAP 4Dx Plus Test. qPCR detected positive results in 12 (37.5 %), whereas ELISA and SNAP 4Dx Plus detected positive results in 10 (31.25 %) and 13 (40.62 %), respectively. Moderate agreement (κ = 0.545) was observed between rTRP36-ELISA and qPCR, and fair agreement (κ = 0.379) between SNAP 4Dx Plus and qPCR. Substantial agreement (κ = 0.79) was found between rTRP36-ELISA and SNAP 4Dx Plus. Compared to qPCR, the sensitivity and specificity of rTRP36-ELISA were 70 % and 77.27 %, respectively, compared to 53.85 % and 73.86 %, respectively, for SNAP 4Dx Plus. Our findings suggest that TRP36 is a promising antigen for <i>E. canis</i> serodiagnosis, potentially improving sensitivity and specificity.