Modeling the effect of test-and-slaughter strategies to control bovine
tuberculosis in endemic high prevalence herds
Abstract
Bovine tuberculosis (bTB) prevalence substantially increased over the
past two decades with relatively high impact on large dairy herds,
raising the concern of regulatory authorities and industry stakeholders,
and threatening animal and public health. Lack of resources, together
with the economic and social consequences of whole-herd stamping-out,
makes depopulation an impractical disease control alternative in these
herds. The increase in bTB-prevalence was associated with demographic
and management changes in the dairy industry in Uruguay, reducing the
efficacy of the current control program (i.e. status quo) based on
intradermal serial testing with caudal fold- and comparative cervical-
tuberculin test-and slaughter of reactors (CFT-CCT). Here, we aimed to
assess the epidemiological effectiveness of six alternative control
scenarios based on test-and-slaughter of positive animals, using
mathematical modeling to infer bTB-within-herd dynamics. We simulated
six alternative control strategies consisting of testing adult cattle
(>1 year) in the herd every three months using one test
(in-vivo or in-vitro) or a combination in parallel of two tests (CFT,
interferon-gamma release assay –IGRA- or Enzyme-linked immunosorbent
assay). Results showed no significant differences overall in the time
needed to reach bTB-eradication (median ranging between 61 to 82 months)
or official bovine tuberculosis-free status (two consecutive negative
herd-tests) between any of the alternative strategies and the status quo
(median ranging between 50 and 59 months). However, we demonstrate how
alternative strategies can significantly reduce bTB-prevalence when
applied for restricted periods (6, 12, or 24 months), and in the case of
IGRAc (IGRA using peptide-cocktail antigens), without incurring on
higher unnecessary slaughter of animals (false-positives) than the
status quo in the first 6 months of the program (P-value
<0.05). Enhanced understanding bTB-within-herd dynamics with
the application of different control strategies help to identify optimal
strategies to ultimately improve bTB-control and -eradication from
dairies in Uruguay and similar endemic settings.