84 A.L. Michel
and dead-end hosts with no significant risk of
intra- or inter-species transmission (Nugent and
Whitford, 2003). Compelling evidence was pro-
vided by various studies. In areas where pos-
sums were controlled by poisoning, tuberculosis
levels in resident feral pigs declined quickly and
fell to near zero within a few years as opposed to
areas without possum control (Nugent and
Whitford, 2008; Nugent et al., 2012). In the
final phase of the Australian tuberculosis eradi-
cation campaign directed at feral buffalo and
cattle in the Northern Territory, the M. bovis
prevalence had not only declined sharply in the
target species but also in sympatric feral pigs, in
which previously infection rates had reached up
to 100% ( McInerney et al., 1995). The use of
pigs as sentinels in a surveillance programme in
high-risk areas for M. bovis along international
borders has been reported from the USA
( Campbell et al., 2011).
Although pig-to-pig transmission probably
exists in New Zealand, it may be very limited and
due to cannibalism rather than to other forms of
horizontal, vertical or pseudovertical transmis-
sion in feral pigs. No evidence of M. bovis excre-
tion via urine, faeces or the nasal cavity could
be found (Lugton, 1997, cited in Nugent and
Whitford, 2003), and no piglets under the age of
2 months have been found infected. A case of a
sow and her piglets being infected turned out to
be genetically unrelated outbreaks, suggesting
scavenging as the underlying source of the
infections (Nugent and Whitford, 2003). The
explanation may be similar where multiple cases
of M. bovis in pigs were encountered on the same
farm in Great Britain (Bailey et al., 2013).
M. tuberculosis infection is a sporadic infec-
tion in swine and an indication of transmission
between humans and pigs. Due to the nature of
the localized lesions in the head lymph nodes, the
infection occurs most likely as the result of spill-
over from the human reservoir with little poten-
tial for spillback. Following the same principles as
M. bovis, the prevalence reflects the epidemio-
logical situation in humans and cases have been
reported from countries with a high tuberculosis
burden in humans including Nigeria (Jenkins
et al., 2011), Ethiopia (Arega et al., 2013) and
South Africa (Michel, unpublished data).
Other incidental infections of pigs with
members of the Mycobacterium tuberculosis com-
plex have been described for M. microti (Taylor
et al., 2006) and M. caprae (Cvetnic et al., 2006;
Rodriguez et al., 2011).6.4 M. bovis Infection in Domestic
Asian Water BuffaloAsian water buffalo (Bubalo bubalis) were domes-
ticated approximately 5000 years ago. Their
natural distribution includes the Indian subcon-
tinent and southeast Asia from where they have
been introduced to Europe, the Americas and
some parts of Africa, mostly Egypt. The suscepti-
bility of water buffalo to M. bovis as well as the
pathogenesis was found to be comparable to
domestic cattle, leading to the assumption that
water buffalo can serve as a reservoir and source
of zoonotic infection to humans (Lall, 1969;
Barbosa et al., 2014; Khattak et al., 2016). The
largest buffalo population in the West is found in
Brazil where M. bovis infection at an animal level
of between 1.4% and 20.4% has been reported
(Barbosa et al., 2014; Minharro et al., 2016),
classifying bovine tuberculosis as cause of
significant economic losses in Brazil.
In India, tuberculosis was historically
widely distributed in water buffalo. A survey
conducted in the 1950s in four states among
40,000 water buffalo revealed a reactor rate of
13.8%. Where cattle and buffalo were kept on
the same farm, infection rates were higher in
buffalo than in cattle (Lall, 1969). In Nepal, cor-
responding infection rates of 16% were found in
water buffalo and cattle with both species spo-
radically excreting M. bovis in milk and faeces
(Jha et al., 2007). Skin testing of water buffalo in
Pakistan revealed a reactor prevalence of 5.7%
(Khattak et al., 2016). Within Europe, water buf-
falo play a locally isolated but important role in
the production of ‘mozzarella di bufala’ cheese
in southern Italy, and the eradication of bovine
tuberculosis from both cattle and buffalo popu-
lations is threatened by a renewed increase in
case incidence of 0.65% (Alfano et al., 2014).6.5 M. bovis Infection in Old
World CamelidsBactrian and dromedary camels are domesti-
cated Old World camelid species. There are today