Activities preceding a decline in the paratuberculosis test prevalence

A voluntary control programme on Mycobacterium avium subsp. paratuberculosis (MAP) was initiated in Denmark in 2006 and has since 2007 included 25-28% of the dairy herds and 35-40% of the dairy cows. The programme was complemented with activities aimed to reduce the MAP infection prevalence. A challenge in evaluation of activities in a national programme it is essentially a sample size of one without a control group.

Therefore, the apparent effect of activities on programme level can only be descriptive. Our objective was to describe the decline in the test-prevalence along with the activities preceding this decline. The cohort of herds enrolled in 2006-2007 had an average estimated within-herd test-prevalence of 10% at start.

By January 2014 this had declined to 2%. The test-prevalence in the cohort of herds enrolled in 2008-2010 started at approximately 6% and by January 2014 was reduced to about 3%. In addition to these data, a “sampling error” in August 2011 resulted in the availability of a sample of 99 herds that were not enrolled in the programme.

They had a median test-prevalence of 5.5% compared to 3.1% in 268 herds from the 2006-2007 cohort tested in the same month. This sample and associated estimates were used to validate that a test prevalence reduction was due to the programme The decline in test-prevalence has been statistically associated to herd-level factors such as low level of livestock purchases and culling of cows deemed to be infectious, but not really to other management factors.

On national level, the first initiatives included training of herd health advisors, information campaigns including various sources of information material and farmer’s meetings. In the last approximately 5 years, the programme has run routinely with few specific extraordinary activities, except for a “continuous” flow of diagnostic test information four times annually in each herd.

This information can be used for detection and management of infectious animals and for prevalence monitoring.