Comparative Evaluation of 2 In-Clinic Assays for Vector-Borne Disease Testing in Dogs.

Vector-borne agents comprise medically important infections affecting dogs throughout much of the world. Sensitive detection of antibodies directed at tick-borne disease-causing organisms in dogs is diagnostically important for veterinarians, pets and their owners, and epidemiologically important for public health surveillance. The SNAP 4Dx Plus Test (IDEXX Laboratories, Inc., Westbrook, ME) identifies antibodies to or infection with multiple tick-borne pathogens and canine heartworm antigen in a single assay. Recently, VetScan FLEX4 Rapid Test (Abaxis, Inc., Union City, CA) was launched as a new assay to detect tick-borne pathogen antibodies and heartworm antigen. In the present study, we evaluated the comparative performance of SNAP 4Dx Plus (SNAP) and FLEX4 Rapid Test (FLEX4) using samples selected based on geographic distributions for canine vector borne diseases, including Borrelia burgdorferi (n = 105), Anaplasma phagocytophilum (160), Anaplasma platys (115), Ehrlichia canis (154), Ehrlichia ewingii (163), Ehrlichia chaffeensis (151) and Dirofilaria immitis (105). Canine vector borne diseases infection status was established for each sample by a combination of reference methods that included necropsy (D. immitis, heartworm disease), Western immunoblotting (B. burgdorferi), immunofluorescence assays (A. phagocytophilum and E. canis) and species-specific ELISAs (A. platys, E. canis, E. ewingii and E. chaffeensis). For comparisons among the 2 assays, samples were evaluated per the manufacturers' instructions for each test kit. By testing each same sample set compared to the defined reference results, sensitivities differed substantially between SNAP and FLEX4, at 95.5 vs. 40.9%, respectively for B. burgdorferi, 97.1% vs. 61.4% for E. canis, 98.2% vs. 59.3% for E. ewingii, 64.3% vs. 35.7% for E. chaffeensis, 84.5% vs. 12.7% for A. phagocytophilum, 83.3% vs. 33.3% for A. platys, and 94.1% vs. 88.2% for D. immitis. Specificities for both rapid assay tests ranged from 98% to 100%. Based upon the comparative results derived from this study, the SNAP test was more sensitive than the FLEX4 test for detection of antibodies to all tick-borne pathogens and heartworm disease (Dirofilaria immitis) antigen in dogs.

Performance of a commercially available in-clinic ELISA for detection of antibodies against Anaplasma phagocytophilum, Anaplasma platys, Borrelia burgdorferi, Ehrlichia canis, and Ehrlichia ewingii and Dirofilaria immitis antigen in dogs.

OBJECTIVE: To evaluate the performance of an in-clinic ELISA designed for detection of heartworm antigen and antibodies against 5 tick-borne pathogens. DESIGN: Validation study. SAMPLE: 1,601 serum or matched serum, plasma, and blood samples from dogs. PROCEDURES: Samples were tested for Dirofilaria immitis (heartworm) antigen and antibodies against Anaplasma phagocytophilum, Anaplasma platys, Borrelia burgdorferi, Ehrlichia canis, and Ehrlichia ewingii by means of an in-clinic ELISA. Evaluation of assay sensitivity and specificity, agreement of results among sample types, and cross-reactivity of E canis antigens in the assay with anti-Ehrlichia chaffeensis antibodies in stored samples from experimentally infected dogs were performed at a reference laboratory. Field tests of the in-clinic ELISA were performed at 6 veterinary facilities. Results were compared with confirmatory test results. RESULTS: Sensitivity and specificity of the in-clinic ELISA were > 89% for detection of antibodies against A phagocytophilum (93.2% and 99.2%, respectively), A platys (89.2% and 99.2%, respectively), B burgdorferi (96.7% and 98.8%, respectively), E canis (97.8% and 92.3%, respectively), and E ewingii (96.5% and 93.9%, respectively). Sensitivity of the assay for detection of D immitis was 98.9%, with 99.3% specificity. The in-clinic ELISA identified exposure to > 1 vector-borne pathogen in 354 of 1,195 samples. Cross-reactivity of E canis antigens with anti-E chaffeensis antibodies was confirmed. Results of field evaluations confirmed that the in-clinic ELISA could be reliably used under typical clinical conditions to identify dogs exposed to the pathogens of interest. CONCLUSIONS AND CLINICAL RELEVANCE: The in-clinic ELISA provided a comprehensive in-house serologic screening test for all vector-borne pathogens evaluated.

Ehrlichia ewingii infection and exposure rates in dogs from the southcentral United States.

We used PCR and a novel serologic assay to determine infection and exposure rates to Ehrlichia ewingii in dogs from an area of northeast Oklahoma and northwest Arkansas where Amblyomma americanum ticks are abundant. Of 143 dogs assayed, 13 (9.1%) harbored E. ewingii by PCR and 64 (44.8%) had antibodies to E. ewingii detected using a peptide-based microtiter plate ELISA. Dogs were more likely (P=0.001) to be positive by PCR if sampled in August (30.8%) but no association was found between seropositive status and month of collection of sample (P>0.05). Additional testing revealed PCR evidence of Ehrlichia chaffeensis (4/143; 2.8%) and Anaplasma platys (5/143; 3.5%) as well as antibodies reactive to E. chaffeensis (25/143; 17.5%), Ehrlichia canis (2/143; 1.4%), and Anaplasma spp. (8/143; 5.6%). Testing of another 200 dogs from the area revealed additional PCR and/or serologic evidence of E. ewingii, E. canis, E. chaffeensis, and A. platys. None of the 343 dogs evaluated had evidence of Borrelia burgdorferi exposure. These data support the interpretation that E. ewingii may be the primary agent of canine ehrlichiosis in this region, and suggest that diagnostic evaluation of dogs suspected to have a tick-borne disease should include assays targeting this organism.