Comparison of an indirect immunofluorescence assay, western blot analysis, and a commercially available ELISA for detection of Ehrlichia canis antibodies in canine sera.
OBJECTIVE
To examine the correlation between results for an indirect immunofluorescence assay (IFA) that uses Ehrlichia canis antigen as a substrate (ie, E canis-IFA), 2 western blot (WB) analyses, and a commercially available ELISA in the detection of E canis antibody in dog sera.


METHODS
54 canine serum samples that were reactive on E canis-IFA and 16 canine serum samples that were E canis-IFA nonreactive.


METHODS
Serum samples were evaluated by use of 2 WB analyses and a commercially available ELISA. Correlation between results of the 3 testing modalities (ie, IFA, WB analyses, and the ELISA) was examined by use of nonreactive (E canis-IFA reciprocal titer, < 20), low-titer (reciprocal titer, 80 to 160), medium-titer (reciprocal titer, 320 to 2,560), and high-titer (reciprocal titer, 5,120 to > 20,480) serum samples.


RESULTS
For all serum samples in the nonreactive (n = 16), medium-titer (17), and high-titer (18) groups, correlation of results among IFA, WB analyses, and the commercially available ELISA was excellent. A poor correlation was found between IFA results and those of WB analyses and the ELISA for serum samples in the low-titer group (19), with only 4 of the 19 serum samples having positive results on both WB analyses and the commercially available ELISA.


CONCLUSIONS
The discrepancy between E canis-IFA, WB analyses, and the commercially available ELISA results for the low-titer serum samples may be related to a high IFA sensitivity or, more likely, a lack of specificity associated with cross-reactivity among Ehrlichia spp.
O'Connor
Thomas P
TP
Department of Research and Development, IDEXX Laboratories Inc, 1 IDEXX Dr, Westbrook, ME 04092, USA.
Hanscom
Jancy L
JL
Hegarty
Barbara C
BC
Groat
Randall G
RG
Breitschwerdt
Edward B
EB
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood*; D015153:Blotting, Western / Q000662:veterinary*; D004283:Dog Diseases / Q000097:blood / Q000175:diagnosis* / Q000276:immunology; D004285:Dogs; D041061:Ehrlichia canis / Q000276:immunology* / Q000302:isolation & purification; D016873:Ehrlichiosis / Q000097:blood / Q000175:diagnosis / Q000276:immunology / Q000662:veterinary*; D004797:Enzyme-Linked Immunosorbent Assay / Q000662:veterinary*; D019084:Fluorescent Antibody Technique, Indirect / Q000662:veterinary*
D000907:Antibodies, Bacterial