CAB International 2018. Bovine Tuberculosis
(eds M. Chambers, S. Gordon, F. Olea-Popelka, P. Barrow) 43
* Email: [email protected]The epidemiology of bovine tuberculosis is, by its
very nature, inconsistent. Mycobacterium bovis is
poorly transmissible between cattle, but has a
high potential for spread due to the chronic
nature of infection. The risk of infection, suscep-
tibility and progression of disease in individual
animals is highly variable but it does vary sys-
tematically with age (Brooks-Pollock et al.,
2013; Downs et al., 2016), breed (Ameni et al.,
2007), host genetics (Allen et al., 2010;
Bermingham et al., 2014) and production type
(Broughan et al., 2016), which in themselves
will vary in different epidemiological contexts.
Resolving the impact of these biological factors
on transmission is difficult as transmission rates,
the duration of latency and the immunological
response of infected animals to diagnostic tests
all compete on timescales comparable to the life
expectancy of the host. As a consequence,
despite rich detailed surveillance data and a
history of study stretching over a century, the
epidemiology of bovine tuberculosis (TB) is still
characterized as much by what we do not know
as it is by what we do.
In this chapter, we critically assess some of
the historic epidemiological data that shaped
many of our views on the epidemiology of
M. bovis in cattle. With reference to simple, and
less simple, epidemiological models, we consider
the strength of different pieces of evidence, theuncertainty that remains and the implications
for control of M. bovis in different contexts.
We begin by reviewing the life history of
infection and routes of transmission of M. bovis
within herds. We then revisit the data from
unmanaged herds endemically infected with
bovine tuberculosis (Francis, 1947) and con-
sider the implications of these data for the likely
patterns of transmission of infection within
herds. We compare these insights to more recent
analyses of transmission in managed herds – in
particular from Great Britain where detailed sur-
veillance and demographic data sets have led to
the development and estimation of several new
models of bovine TB transmission both within
and between herds. Finally, we consider the role
that infection in sympatric wildlife populations
has for both the inference of patterns of trans-
mission within cattle populations and the pros-
pects for control.4.1 Life History of Infection and
TransmissionComstock, Levesay and Woolpert described
human tuberculosis as an infectious disease
where ‘the incubation period... ranges from a
few weeks to a lifetime’ (Comstock et al., 1974).4 The Epidemiology of Mycobacterium
bovis Infection in Cattle
Andrew J.K. Conlan* and James L.N. Wood
Disease Dynamics Unit, Department of Veterinary Medicine, University of
Cambridge, Cambridge, UK