Abstract
The Republic of Ireland reports a relatively low prevalence of Johne’s disease (JD) compared to international counterparts. Postulated reasons for this include a lower average herd size and a grass-based production system. Ireland also engages in high levels of bovine tuberculosis (bTB) testing. As interferon-gamma (IFN-γ) is believed to play a key role in protecting against JD, it is our hypothesis that administration of purified protein derivative (PPD), as part of the bTB test, is associated with a systemic increase in IFN-γ production, which may potentially limit clinical progression of the disease. We studied 265 cows (202 Friesian and 63 “Non-Friesian,” e.g., JerseyX, Norwegian Red) to assess IFN-γ levels and Mycobacterium avium subspecies paratuberculosis (MAP) antibody response before and after the bTB test. As part of the compulsory annual bTB test, avian and bovine PPD were administered at two separate cervical sites. To assess IFN-γ production, blood samples were taken before and 72 h after PPD administration. MAP antibody response was assessed before and 10 days post-PPD administration. A significant increase in MAP antibody response was identified post-bTB compared to pre-bTB response (p < 0.001). Additionally, IFN-γ production significantly increased at the post-bTB time point (p < 0.001) compared to the pre-bTB test readings. This may indicate a beneficial effect of bTB testing in controlling JD.
Highlights
Mycobacteria are a leading cause of debilitating infections in domesticated animals and wildlife [1]
A total of two animals were classified as inconclusive on single intradermal cervical comparative test (SICCT) but none were classified as bovine tuberculosis (bTB) positive
The current study only examined the response at day 10 post-purified protein derivative (PPD) administration, but previous research on Irish dairy herds [24] has recommended avoiding testing for Mycobacterium avium subspecies paratuberculosis (MAP) antibodies until day 71 post PPD to avoid potential interference with MAP ELISA results
Summary
Mycobacteria are a leading cause of debilitating infections in domesticated animals and wildlife [1]. Certain mycobacteria have public health implications, such as bovine tuberculosis (bTB). Compulsory eradication schemes were initiated in the Republic of Ireland in the 1960s to both protect human health and agricultural exports [2]. Levels of TB in the human population in Ireland have dramatically reduced in the past 50 years, bTB eradication remains necessary in order to comply with European trading conditions (Directive 64/432 EEC) [2]. Bovine tuberculosis is caused by Mycobacterium bovis (M. bovis). In the late 1800s, Robert Koch identified the tubercle bacillus and developed tuberculin, a glycerol extract of pure culture of tubercle bacilli [3]. The intradermal skin test has been used diagnostically for detection of human and bovine TB for over 100 years. Performed using Koch’s Old tuberculin, a more stable
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