Cattle husbandry in Ethiopia is a predominant factor affecting the pathology of bovine tuberculosis and gamma interferon responses to mycobacterial antigens

Abstract

Bovine tuberculosis is a major economic problem and a potential public health risk. Improved diagnostics like the gamma interferon (IFN-gamma) test with ESAT6 and/or CFP10 could contribute to the control program. We assessed IFN-gamma responses in zebu (Ethiopian Arsi breed) and Holstein cattle kept indoors or in a pasture to tuberculin purified protein derivative (PPD) and an ESAT6-CFP10 protein cocktail. Furthermore, the intensity and distribution of pathology of bovine tuberculosis were compared between the two breeds. Our data demonstrated significantly (all P < 0.02) higher IFN-gamma responses to avian PPD, bovine PPD, and the ESAT6-CFP10 protein cocktail in Holstein than in zebu cattle, while lesion severities in infected animals and tuberculin skin test responses did not differ significantly (P > 0.05) between the two breeds. Holstein cattle that were kept indoors produced significantly (all P < 0.01) higher IFN-gamma levels in response to avian PPD, bovine PPD, and the ESAT6-CFP10 protein cocktail than did Holstein cattle kept in a pasture. Moreover, lesion severity was significantly higher in Holstein cattle kept indoors (P = 0.001) than in those kept in the pasture. Lesions were localized predominantly in the digestive tract in cattle kept in a pasture, while they were localized in the respiratory tract in cattle kept indoors. In conclusion, in Holstein cattle, husbandry was a dominant factor influencing the severity of tuberculosis lesions and IFN-gamma responses to mycobacterial antigens compared to breed. A difference in the cellular immune response between zebu and Holstein cattle was observed, while tuberculosis lesion severities were identical in the two breeds, when both were kept in a pasture.

FIG. 1.

IFN-γ response to mycobacterial antigens in Holstein and zebu cattle kept in a pasture. Whole-blood cultures were stimulated with avian PPD, bovine PPD (both used at 10 μg/ml), and an ESAT6-CFP10 protein cocktail (each protein at 5 μg/ml). Positive control, PHA (5 μg/ml). IFN-γ was determined by the Bovigam enzyme immunoassay, and results are expressed as the mean ± the standard error of the mean. *, P < 0.02. OD, optical density.

FIG. 2.

Comparative intradermal tuberculin test results for Holstein and zebu cattle. Changes in skin thickness after application of avian PPD and bovine PPD were measured in millimeters. In addition, the differences between reaction sizes at the bovine PPD injection site and the avian PPD injection site (PPD B − PPD A) are also shown.

FIG. 3.

IFN-γ response to mycobacterial antigens in Holstein cattle kept indoors or in a pasture. Whole-blood cultures were stimulated with avian PPD, bovine PPD (both used at 10 μg/ml), or an ESAT6-CFP10 protein cocktail (each protein at 5 μg/ml). Positive control, PHA (5 μg/ml). IFN-γ was determined by the Bovigam enzyme immunoassay, and results are expressed as the mean ± the standard error of the mean. *, P < 0.01. OD, optical density.

FIG. 4.

Mean pathology scores of the lymph nodes and other organs of Holstein cattle kept indoors or in a pasture. Pathology scores were determined as defined by Vordermeier et al. (27), and mean scores of individual lung lobes or lymph nodes are shown. Results are expressed as the mean score of each tissue type ± the standard error of the mean. URT, upper respiratory tract; LRT, lower respiratory tract; AT, alimentary tract.

FIG. 5.

Relationship between IFN-γ responses and severity of pathology. (A) IFN-γ responses to bovine PPD and pathology of bovine TB in Holstein cattle kept in a pasture (Spearman's r = 0.487, P = 0.018). (B) IFN-γ responses to bovine PPD and severity of pathology of bovine TB in Holstein cattle kept indoors (Spearman's r = −0.262, P = 0.1945). OD, optical density.