Managing Bovine Tuberculosis: Successes and Issues 239
In 2016, the World Health Organization
(WHO) reported that 10.4 million people became
ill and 1.8 million people died from TB (World
Health Organization, 2016). Sixty percent of
new TB cases occurred in just six countries:
China, India, Indonesia, Nigeria, Pakistan and
South Africa. In 2014 the WHO developed and
accepted the ‘End TB Strategy’ (World Health
Organization, 2014) which supports the UN’s
poverty reduction policy. The WHO strategy has
targets for: (i) a 75% reduction in the number of
tuberculosis (TB)-related deaths and a 50%
reduction in the TB incidence rate over the
period 2015–2025; and (ii) a 95% reduction in
tuberculosis deaths and a 90% reduction in TB
incidence by 2035.
The WHO End TB Strategy is targeted at
reducing TB caused by M. tuberculosis, and
recently, in 2016, for the first time recognized
and included M. bovis as a cause of disease in
humans. However, on a global level the caus-
ative organism is still not being differentiated to
the species level for the vast majority of human
TB cases. From a practical point of view, it is
important to further investigate the conse-
quences of misdiagnosing M. bovis infection and
its implications for the outcome of any TB treat-
ment regime.
Cosivi et al. (1998) reported that between
1954 and 1970, M. bovis was responsible for
3.1% of human TB cases worldwide. Since then,
the percentage of human cases attributable to
M. bovis in high GNI countries is likely to have
fallen significantly. The trend in low to medium–
high GNI countries is unknown, but widespread
HIV/AIDS infection is likely to have exacerbated
both M. tuberculosis and M. bovis infection levels.
Snippets of data from these countries arising
from targeted non-representative studies indi-
cated that the proportion of M. bovis isolated
from human TB cases in largely rural areas
ranged between 3.9% and 10% in Nigeria, 0.4%
and 45% in Egypt and up to 36% in Tanzania
(Cosivi et al., 1998), and between 16.3% and
29.2% in Ethiopia (Shitaye et al., 2007) (see also
Chapter 3). Cook et al. (1996) found that there
was a seven times greater risk of TB in humans
in households in Zambia possessing tuberculin-
positive cattle (odds ratio of 7.6). Cosivi et al.
(1998) also identified that in low to medium–
high GNI economies in Africa and Asia, between
82% and 94% of the human population lived in
rural areas where there was very little or no con-
trol or management of TB in cattle. Given the
increased demand for local milk in these coun-
tries, the authors identified cattle as a potential
source of TB for humans. This is supported by
Shitaye et al. (2007) who indicated that due to
widespread HIV/AIDS in Ethiopia and other
African countries, affected humans may have an
increased chance of becoming infected with
M. bovis from consuming raw milk, raw meat
and blood from potentially infected animals
( Mfinanga et al., 2003). Furthermore, Chen et al.
(2009) reported finding M. tuberculosis in cattle
in China that had an epidemiological link to
human M. tuberculosis infection. M. tuberculosis
and M. bovis have both also been isolated from
TB lesions from goats in Nigeria (Cadmus et al.,
2009) and Ethiopia (Deresa et al., 2013). There-
fore, the finding of both M. bovis and M. tubercu-
losis in cattle and in goats in low to medium–high
GNI economies poses a potential challenge to the
WHO End TB Strategy unless TB in livestock is
also addressed. Future reduction in levels of
human TB is likely to depend upon identifying
and controlling the source of infection, despite
this being of low importance for treatment
purposes.
In order for the WHO End TB Strategy tar-
gets to be met, it is likely that human M. bovis
cases will need to be reduced in low to medium–
high GNI countries. Despite the fact bovine TB
no longer poses a zoonotic risk in most high GNI
economies compared to low to medium GNI
countries, because most milk is pasteurized,
meat is inspected following slaughter, and
national test-and-slaughter programmes for
cattle are in place. It is worth noting that in the
USA, M. bovis continues to be a source of human
TB although it is possible that a considerable
proportion of these cases may have been
acquired abroad (Scott et al., 2016).
In considering strategies to reduce the risk
of M. bovis spreading within livestock and to
humans in low to medium–high GNI economies,
it is important to take account of available dis-
ease management resources and the willingness
of cattle owners to accept disease control inter-
ventions. No single strategy will suit all situa-
tions, with feasible options ranging from simple
information gathering and dissemination,
through to a comprehensive test-and-slaughter
programme. Primary goals should be to reduce