Mycobacterium bovis as the Agent of Human Tuberculosis: Public Health Implications 19
comparability of such studies is diminished;
hence, the available estimates regarding the bur-
den of zoonotic TB may not accurately represent
the true incidence of this disease.
Despite the limitations with the quality and
representativeness of currently available data
regarding the global scenario for zoonotic TB,
the estimated incident number of cases is con-
cerning. The first comprehensive global esti-
mates of the burden of zoonotic TB caused by
M. bovis in people were published in 2015 by the
WHO as part of the Global Burden of Foodborne
Disease (Kirk et al., 2015; WHO, 2015b). These
estimates were derived from the systematic
review conducted by Müller et al. (2013) of pub-
lished data to estimate proportions of TB patients
with zoonotic TB in different settings and iden-
tify countries endemic for bovine TB, which were
then applied to WHO estimates of incidence and
mortality of all forms of TB during 2010. The
estimated global annual incidence of zoonotic
TB was 121,268 (95% uncertainty interval:
99,852–150,239), with a median rate of 2
(95%UI: 1–4) new cases per 100,000 popula-
tion per year. The highest population-level inci-
dence was in the WHO African region, with an
estimated median of 7 (95% UI: 4–9) new cases
per 100,000 population. Additionally, 607,775
(95%UI: 458,364–826,115) disability-adjusted
life-years (DALYs), representing healthy years of
life lost due to illness, were estimated to be attrib-
uted to zoonotic TB globally. In the African
region, this was estimated as 30 (95%UI: 19–42)
DALYs per 100,000 population (WHO, 2015b).
The annual estimated global mortality due to
M. bovis during 2010 was 10,545 (95% UI:
7894–14,472). In 2016, for the first time, the
annual WHO Global TB Report presented the
incidence of human TB caused by M. bovis. For
the year 2015, there were an estimated 149,000
new cases (95% uncertainty interval: 71,600–
255,000) and 13,400 deaths (95% uncertainty
interval: 5050–27,500). It is worth noting that
the estimated number of people suffering annu-
ally from zoonotic TB largely exceeds the num-
ber of people affected by other diseases that
receive greater attention, funding, and resources
(WHO, 2012; von Philipsborn et al., 2015).
Despite these available estimates and likely wide-
spread geographical distribution of associated
zoonotic TB risk factors, M. bovis as a causal
agent of human TB has remained largely
ignored in the vast majority of low-income, high
TB burden countries where bovine TB is also
endemic.
The global incidence of zoonotic TB will
continue to be updated annually by WHO based
on the most recent estimation of the incidence
of all forms of TB. However, there is a need for
better quality national data in order to fully
understand the true burden of disease, particu-
larly in regions where bovine TB is endemic. It
must also be remembered that the above esti-
mates of disease only represent one component
of the total impact of M. bovis. Reduced livestock
productivity, economic losses and trade barriers
due to infection in livestock must also be
accounted for when considering the full scope of
the disease. These aspects of zoonotic TB are
covered in Chapters 1, 3 and 4 in this volume.2.3 Socio-cultural and Demographic
Factors Associated with Zoonotic TB
Caused by M. bovisThe epidemiology and risk factors increasing the
risk of human TB caused by M. bovis vary
according to social, cultural and economic fac-
tors (Michel et al., 2009; Ayele et al., 2014).
M. bovis infection in humans can be acquired
both orally and via inhalation of aerosolized
particles containing M. bovis from infected ani-
mals (Biet et al., 2005) or rarely from person-to-
person contact (LoBue et al., 2003; Evans et al.,
2007).2.3.1 Consumption of unpasteurized
dairy productsThe most common route of infection of M. bovis
is through the oral route by consumption of
contaminated milk or other dairy products
(Acha and Szyfres, 1987). Thus, milk pasteuri-
zation plays a crucial role in preventing human
infection (O’Reilly and Daborn, 1995; Collins,
2006). Pasteurization of milk, however, is often
inaccessible in many low-income countries or in
rural communities around the world. Although
the boiling of milk at home provides sufficient
pasteurization, this requires access to a fuel
source. Ben et al. (2011) demonstrated the