Evaluation of potential predictor variables for PCR assay diagnosis of Anaplasma phagocytophilum infection in equids in Northern California.

The research article discusses an evaluation of potential factors that may predict the presence of Anaplasma phagocytophilum infection in equids, utilizing a PCR assay result, in Northern California.

Research Purpose and Methodology

The purpose of this study was to identify clinical or clinicopathologic variables associated with a positive PCR (Polymerase Chain Reaction) assay result for Anaplasma phagocytophilum infection in equids (horses, donkeys, and related animals). This bacteria typically causes a disease called anaplasmosis. The study was conducted by examining the medical records of 162 equids, which had undergone testing for A. phagocytophilum infection via a PCR assay between June 1, 2007, and December 31, 2015.

• For each equid that tested positive (defined as a ‘case equid’), two corresponding equids that were tested in the same timeline but resulted negative (termed ‘control equids’) were identified.
• Data was collected regarding various aspects of each equid – age, sex, breed, geographic location at the time of testing, physical examination findings, complete blood count (CBC), and plasma biochemical analysis results.
• Potential predictor variables from this collected data were analyzed using stepwise logistic regression, generalized additive models, and classification and regression tree analysis.

Findings

The study concluded that variables such as total lymphocyte count, plasma total bilirubin concentration, plasma sodium concentration, and geographic latitude turned out to be linear predictors of a positive PCR result for A. phagocytophilum. On the other hand, Plasma creatine kinase activity was a nonlinear predictor of a positive result.

Impact and Clinical Relevance

• This study has significant implications in a clinical setting as the identified predictors can help veterinarians recognize equids that could benefit from early treatment for anaplasmosis while waiting for the definitive test results.
• Simultaneously, this knowledge base could also prevent wasteful usage of antibiotics like oxytetracycline in equids who are not likely to test positive for the disease.