Bovine Tuberculosis in Other Domestic Species 81
Before the introduction of national bovine
tuberculosis control and eradication pro-
grammes when large proportions of the Euro-
pean cattle herds were infected with M. bovis, the
prevalence of goats with tuberculosis slaugh-
tered did not exceed 1% (Myers and Steele, 1969;
Huitema, 1988) and tuberculosis in sheep was
barely known. In North and South America,
Asia and Australia the disease also seemed to be
very rare and associated with the occurrence of
widespread tuberculosis in cattle (Myers and
Steele, 1969; Nanda & Gopal Singh, cited in Lall,
1969; O’Reilly and Daborn, 1995).
In recent decades, a broader geographical
distribution of M. bovis infection in goats and
sheep has been reported including Africa (van
den Heever, 1984; Cadmus et al., 2009; Hiko
and Agga, 2011; Naima et al., 2011; Boukary
et al., 2012), South America (Higino et al.,
2011), New Zealand (Cordes et al., 1981; David-
son et al., 1981), Sudan (Tag el Din and el Nour
Gamaan, 1982), Pakistan (Javed et al., 2010)
and Europe (Shanahan et al., 2011; Van Der
Burgt et al., 2013) with an emphasis on Mediter-
ranean countries (Muñoz Mendoza et al., 2012;
Zanardi et al., 2013).
Apart from M. bovis, M. caprae is the main
causative agent of tuberculosis in goats and
sheep (Bezos et al., 2014). Since its discovery in
Spain (Aranaz et al., 1999) and elevation to
species level as an independent member of the
M. tuberculosis complex (MTBC) (Aranaz et al.,
2003) it has also been reported to infect other
domestic and wild animal species as well as
humans mainly in Europe (Pate et al., 2006;
Cvetnic et al., 2007; Rodriguez et al., 2011). In
Spain it is responsible for 7.4% of MTBC isolates
whereby the epidemiology is driven by caprine
infections (Rodriguez et al., 2011).
It was generally accepted that outbreaks in
sheep or goats were the result of spillover from
bovine TB reservoir species, whether domestic or
wild (Cordes et al., 1981; Malone et al., 2003).
While this route of transmission is probably a
reality in many cases, it should not distract from
the potential of both sheep and goats to act as
reservoir hosts under certain conditions (Napp
et al., 2013). Intensification of dairy goat pro-
duction has led to large herd sizes often housed
all year and resulting in high animal densities
facilitating rapid spread of infection among
goats. As a result, high within-herd prevalences
and mortality rates of up to 50% are not uncom-
mon and cause severe economic losses to pro-
ducers (Crawshaw et al., 2008; Quintas et al.,
2010; Bezos et al., 2014; Harwood, 2014).
In contrast, sheep are mostly managed
extensively, and while their species-specific
behaviour is usually a limiting factor to inciden-
tal M. bovis exposure from other infected hosts,
infections do occur where sheep share their
environment with cattle herds infected with
high M. bovis prevalence (Cordes et al., 1981;
Malone et al., 2003). Under these circumstances,
M. bovis is transmitted either by aerosol or by
ingestion and results in encapsulated granulo-
matous lesions, occasionally with mineralized
foci, in the respiratory tract and mesenteric
lymph nodes.
Clinical signs in goats include dry cough
and progressive emaciation, whereas tuberculo-
sis in sheep remains generally unnoticed. The
lesions are mostly located in the lungs and their
draining lymph nodes where they present as
caseous lymphadenitis with nodules of various
sizes with a yellowish–white, moist appearance.
Several reports have described liquifactive necro-
sis and cavitary lung lesions filled with exudate
as typical features of tuberculosis in goats
( Daniel et al., 2009; Domingo et al., 2014)
which, according to Sanchez (2011) is similar to
human tuberculosis and contributes to a high
transmissibility of the disease. The occasional
occurrence of mammary tuberculosis raises a
public health concern for consumers of goat
milk (Huitema, 1988).
On rare occasions, M. tuberculosis infection
has been reported in goats in the UK (Crawshaw
et al., 2008) and Africa (Cadmus et al., 2009;
Hiko and Agga, 2011; Kassa et al., 2012). In an
experimental infection study, Bezos and co-
workers challenged goats with M. bovis, M. cap-
rae and M. tuberculosis and showed that although
M. tuberculosis induced specific pathology, the
lesion scores were lowest for M. tuberculosis
(Bezos et al., 2015). This may suggest that goats
contract M. tuberculosis from close contact with
infected humans, but they are a dead-end or
spillover host and have no significant role to play
in the epidemiology of M. tuberculosis. In the
zoonotic context, goats have been implied to
serve as source of human infection with M. bovis
(Gutierrez et al., 1997) and M. caprae (Nebreda
et al., 2016). However, little is known about the