Poster Title

The use of IgG(T) as a diagnostic tool in foals with naturally acquired Rhodococcus equi pneumonia.

Grade Level at Time of Presentation

Senior

Institution

University of Kentucky

KY House District #

77

KY Senate District #

28

Department

Department of veterinary sciences

Abstract

While rhodococcal pneumonia is among the leading causes of foal mortality, its diagnosis remains a challenge. Antibodies specific to VapA (virulence-associated protein A) were previously evaluated as a diagnostic tool using foals that had been challenged with R. equi. With the exception of IgG(T), VapA-specific IgG subclasses were poor predictors of disease. The objective of this study was to further investigate the use of IgG(T) as a diagnostic tool under field conditions. Healthy foals on a farm with a history of endemic R. equi infections were enrolled in the study (n=46). A serum sample from each foal was collected monthly at ultrasound screening times or when a trans-tracheal wash was performed. Sample collection was discontinued when antibiotic therapy for rhodococcal pneumonia was begun. Additional positive control serum samples were obtained from confirmed cases of rhodococcal pneumonia admitted to a local hospital (n=3). All samples were analyzed utilizing a previously validated ELISA for VapA-specific IgG and its subclasses (IgGa, IgGb, and IgG(T)). Foal’s were classified into one of the four groups: no respiratory abnormalities, subclinical disease, rhodococcal pneumonia, non-rhodococcal pneumonia. One-way ANOVA was used to compare the concentrations of VapA-specific IgG and its subclasses amongst the four different groups at each time point with significance level stablished at α=0.05. No statistical differences were identified and only 2/5 foals with rhodococcal pneumonia had elevated IgG(T) at four months of age. No foals without respiratory abnormalities (32), or with non-rhodococcal pneumonia (1) had high IgG(T) concentrations. Thus, IgG(T) was a poor indicator of rhodococcal pneumonia within the studied population. One factor that may have contributed to these results is the high number of subclinical foals that were started on treatment based solely on ultrasonographic abnormalities or on unspecific clinical signs. Therefore, it is possible that the early removal of these foals precluded our detection of a significant IgG(T) response.

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The use of IgG(T) as a diagnostic tool in foals with naturally acquired Rhodococcus equi pneumonia.

While rhodococcal pneumonia is among the leading causes of foal mortality, its diagnosis remains a challenge. Antibodies specific to VapA (virulence-associated protein A) were previously evaluated as a diagnostic tool using foals that had been challenged with R. equi. With the exception of IgG(T), VapA-specific IgG subclasses were poor predictors of disease. The objective of this study was to further investigate the use of IgG(T) as a diagnostic tool under field conditions. Healthy foals on a farm with a history of endemic R. equi infections were enrolled in the study (n=46). A serum sample from each foal was collected monthly at ultrasound screening times or when a trans-tracheal wash was performed. Sample collection was discontinued when antibiotic therapy for rhodococcal pneumonia was begun. Additional positive control serum samples were obtained from confirmed cases of rhodococcal pneumonia admitted to a local hospital (n=3). All samples were analyzed utilizing a previously validated ELISA for VapA-specific IgG and its subclasses (IgGa, IgGb, and IgG(T)). Foal’s were classified into one of the four groups: no respiratory abnormalities, subclinical disease, rhodococcal pneumonia, non-rhodococcal pneumonia. One-way ANOVA was used to compare the concentrations of VapA-specific IgG and its subclasses amongst the four different groups at each time point with significance level stablished at α=0.05. No statistical differences were identified and only 2/5 foals with rhodococcal pneumonia had elevated IgG(T) at four months of age. No foals without respiratory abnormalities (32), or with non-rhodococcal pneumonia (1) had high IgG(T) concentrations. Thus, IgG(T) was a poor indicator of rhodococcal pneumonia within the studied population. One factor that may have contributed to these results is the high number of subclinical foals that were started on treatment based solely on ultrasonographic abnormalities or on unspecific clinical signs. Therefore, it is possible that the early removal of these foals precluded our detection of a significant IgG(T) response.