A study by a group of NI-based scientists has found that Johne’s disease could be negatively affecting bovine tuberculosis (bTB) eradication. The report highlights that bTB breakdown herds in NI were at an increased risk of being infected with Johne’s disease, and this could also be affecting the accuracy of the skin test. Blood samples from 4,500 herds in NI were retrospectively tested for Johne’s, and bTB was identified through skin test results and post-mortem analysis.

These data form part of an emerging evidence base to suggest that Johne’s disease, could be impacting on the dynamics of bTB in cattle herds

The study found that 45.2% of bTB breakdown herds were positive for Johne’s infections, whereas only 36.0% of herds that were not down with bTB at the time of testing had Johne’s-causing bacteria present.

“These data form part of an emerging evidence base to suggest that Johne’s disease could be impacting on the dynamics of bTB in cattle herds, and consequently has a negative impact on bTB disease eradication,” the scientists state.

Johne’s is an infectious intestinal disease in ruminants, which can be hard to identify as it has a long incubation period.

The study, conducted by scientists from the Agri Food and Biosciences Institute, Queen’s University Belfast and Animal Health and Welfare NI, also provided further evidence that Johne’s can impact the bTB skin test.

This masking effect may impact on the ability to identify exposed cattle, cull them, and thus clear infection

The peer-reviewed paper, published in Frontiers in Veterinary Science, states that the current scientific consensus is that co-infection with Johne’s reduces the sensitivity of bTB skin tests, which can lead to more bTB-infected animals not being identified.

“This masking effect may impact on the ability to identify exposed cattle, cull them, and thus clear infection,” the paper reads.

However, the study states that Johne’s may also negatively impact on specificity of the skin test, which could lead to more false positive reactors being removed from herds.

The scientists point out that this could increase bTB disclosure rates and could result in non-infected herds being incorrectly classified as having a bTB breakdown.

“Further research is required to better understand how these patterns emerge and to definitively establish causation,” the study concludes.

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