Serologic testing of horses for granulocytic ehrlichiosis, using indirect fluorescent antibody staining and immunoblot analysis

Objective-To diagnose granulocytic ehrlichiosis in horses, compare results of indirect fluorescent antibody (IFA) staining procedures with those of im munoblot analysis, and compare serologic test findings with polymerase chai n reaction (PCR) results, Animals-69 horses with high rectal temperatures (greater than or equal to 3 9 C) and lethargy, anorexia, or limb edema. Procedure-43 convalescent serum samples obtained from 38 horses 2 to 18 wee ks after onset of illness were analyzed by use of immunoblot procedures and IFA staining methods, using the NCH-1 or BDS ehrlichial strains, Blood sam ples from 69 acute ly ill horses were tested by PCR to detect ehrlichial DN A, Results-Antibodies to Erlichial equi were detected in serum samples obtaine d during ail seasons; seropositivity rates ranged from 50 to 93%. in IFA as says using the BDS or NCH-1 strain, seropositivity rates were 70 and 79%, r espectively, whereas in immunoblot analyses using the NCH-1 strain, a serop ositivity value of 79% was recorded. By immunoblot analysis, all serum samp les of all seropositive horses were reactive to a protein having molecular mass of about 44 kd. Blood samples from 29 of 69 (42%) acutely ill horses c ontained ehrlichial DNA, Conclusion and Clinical Relevance-Results of the various serologic testing procedures were in close agreement with each other. All serologic testing m ethods are suitable for laboratory diagnosis of equine granulocytic ehrlich iosis.