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

The research article focuses on the testing methods used to diagnose granulocytic ehrlichiosis, a bacterial disease, in horses. The techniques compared in this study are indirect fluorescent antibody (IFA) staining, immunoblot analysis, and polymerase chain reaction (PCR) tests, with the results indicating that all the methods are effective for laboratory diagnosis.

Study Methods

The researchers used multiple techniques to gather data for this study.

• The subjects of the study were 69 horses presenting symptoms of high rectal temperatures, lethargy, anorexia, or limb edema. These symptoms are typical of granulocytic ehrlichiosis.
• Convalescent serum samples were obtained from 38 of the horses ranging from 2 to 18 weeks after symptoms appeared. These samples were analyzed using both IFA staining methods and immunoblot procedures.
• The staining and immunoblot procedures were conducted using either the NCH-1 or BDS ehrlichial strains. These strains refer to types of bacteria that cause granulocytic ehrlichiosis.
• Separately, blood samples from the 69 initially ill horses were assessed using PCR to detect the presence of ehrlichial DNA. This helps confirm the presence of granulocytic ehrlichiosis.

Study Results

The results of this study demonstrated that various methods of serologic testing were effective in detecting granulocytic ehrlichiosis.

• Across all seasons, antibodies to Ehrlichial equi (a bacterium causing the disease) were detected in serum samples. The rates of detection ranged from 50% to 93%, indicative of the prevalence of the disease among the tested population.
• The IFA assays’ seropositivity rates, whether using the BDS strain or the NCH-1 strain, were 70% and 79% respectively. In other words, these tests indicated that a significant percentage of the horses had antibodies against these strains, signifying they had been infected.
• Immunoblot analyses using the NCH-1 strain also showed a seropositivity value of 79%, consistent with the IFA test results.
• All serum samples of seropositive horses presented a reaction to a protein weighing around 44kd. This protein is likely related to the ehrlichiosis infection.
• Of the 69 acutely ill horses, 42% had ehrlichial DNA present in their blood samples, as detected by PCR tests.

Conclusions and Implications

• All the serologic testing procedures provided similar results, suggesting a high level of reliability and effectiveness in diagnosing granulocytic ehrlichiosis in horses.
• The congruence of these results indicates that these testing methods could be effectively used in a laboratory setting for this purpose.