One third of Irish cattle herds which had bovine TB restrictions lifted suffered another TB breakdown within three years, researchers in UCD have found.
Staff from the Centre for Veterinary Epidemiology and Risk Analysis (CVERA) studied figures from all herds restricted due to TB in 1998, 2008 and 2012 and compared the number to those who had another breakdown within three years.
Figures from the study showed the percentage of herds affected by a second infection declined in the last 20 years.
In 1998, 47% of herds had a subsequent restriction by 2001. For herds monitored in 2008, 35% suffered a second restriction by 2011. The most recent data from 2012 to 2015 showed the rate of reinfection declined to 30%.
The study identified two major risk factors for reinfection. The first was residual infection, where cattle were infected but were missed during TB testing. The second was reinfection from local sources, such as neighbouring farms or wildlife, or from infected cattle being purchased.
It was found that larger herds were more likely to suffer a reinfection. In herds with 34 animals or less the risk of TB recurrence dropped to 26%. In herds of over 100 animals the risk of recurrence rose to 43%.
Researchers said the reasons for this were not entirely clear but it has been suggested larger herds “may increase opportunity for exposure, both within the herd and from neighbouring herds”.
The risk of a subsequent breakdown was affected by herd type as well as size.
It was recommended that a similar analysis be conducted in three to five years to evaluate the impact of changes to the TB eradication programme
In cases where a suckler herd suffered a TB breakdown, 32% had a further breakdown within three years. For dairy herds the number who had a second breakdown rose to 45%.
It was recommended that a similar analysis be conducted in three to five years to evaluate the impact of changes to the TB eradication programme. Upcoming changes to the future programme include a nationwide vaccination programme for badgers and increased controls on movements from high-risk herds.
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