Paratuberculosis (PTB) is a severe, slow-developing, untreatable disease of ruminants.
Worldwide, the disease affects more than 50% of herds in the dairy industry, and causes
substantial economic losses for dairy producers. Diagnostic tests show limited sensitivity,
especially in the early stages of the disease. Our study aimed to investigate the
seroprevalence of Mycobacterium avium ssp. paratuberculosis (MAP) in large-scale dairy
herds in Hungary, in association with the self-reported presence or absence of screening
and intervention measures against MAP transmission. We processed data from 42 large-scale
Holstein Friesian farms in Hungary between 1 January 2018 and 31 December 2021. An
average of 32,009 (min.: 31,702; max.: 32,207) animals were blood sampled yearly (127,372
in total during the four years), corresponding to 15% of the Hungarian dairy cattle
population. All female cattle older than 2 years were blood sampled on the farms enroled
in the study. The samples were tested using a commercial ELISA (IDEXX paratuberculosis
screening Ab test). Farm managers were interviewed about their on-farm diagnostic
and intervention approaches using a uniform questionnaire, including questions on
the level of awareness, frequency of ELISA and PCR testing, and their strategies for
culling adult animals and reducing transmission to newborn calves. By comparing the
annual rate of change in seroprevalence and the amount of change observed during the
four-year period, we concluded that test-and-cull strategies implemented in parallel
with newborn calf management that aimed at preventing MAP transmission were superior
to test-and-cull strategies alone; moreover, fortifying culling decision making via
additional ELISA and PCR tests is superior to using a single ELISA result. For farms
that carried out a complex program with both “test-and-cull” and proper newborn calf
management, there was a proportional reduction in apparent seroprevalence at an average
of 22.8% per year. Fifteen of the sampled farms had no measures in place to control
paratuberculosis. On these farms, the seroprevalence increased by 12.1% per year on
average.
