96 N.J. Fox et al.
been identified in the excretory ducts of the
mandibular salivary glands of wild boar
( Martín-Hernando et al., 2007). Given the distri-
bution of lesions, respiratory infection from
direct social contacts is possible as social family
groups roam and forage together (Vicente et al.,
2013). In contrast, transmission through urine
is unlikely, as neither lesions nor mycobacteria
have been found in wild boar kidneys (Naranjo
et al., 2008). Numerous suid behaviours pro-
mote ingestion and inhalation of M. bovis bacilli,
including their broad dietary spectrum (Dondo
et al., 2007) and penchant for rooting and wal-
lowing in muddy water, where M. bovis can sur-
vive outside the host (Young et al., 2005). Wild
boar also have a predilection for carrion con-
sumption, and it is likely that scavenging carrion
and hunted animal remains left in the field plays
an important role in transmission (Vicente et al.,
2007b).
7.1.4 DeerConsistent with the broad host range, M. bovis
infection has been reported in at least 14 species
of deer, including red deer (Cervus elaphus),
North American elk (Cervus elaphus nelsoni), tule
elk (Cervus elaphus nannodes), sika deer (Cervus
nippon), sambar deer (Cervus unicolor swinhoei),
fallow deer (Dama dama), white-tailed deer
(Odocoileus virginianus), mule deer (Odocoileus
hemionus), black-tailed deer (Odocoileus hemionus
columbianus), axis deer (Axis axis), roe deer
( Capreolus capreolus), Chinese muntjac deer
(Muntiacus reevesi), reindeer (Rangifer tarandus)
and moose (Alces alces) (Palmer et al., 2015).
Severe outbreaks in wild deer are uncommon,
and less frequent than in captive deer (Griffin
and Buchan, 1994; Hunter, 1996).
The majority of data on wild deer hosts are
from white-tailed deer in North America as they
are believed to play an important role in disease
maintenance, especially in areas of Michigan
where M. bovis is endemic in the white-tailed
deer population (Conner et al., 2008). M. bovis
infection in deer has also been studied widely in
other regions, including the UK (Delahay et al.,
2007), Spain (Vicente et al., 2006; Martín-
Hernando et al., 2010) and New Zealand (Griffin
and Buchan, 1994; Lugton et al., 1998).
Prevalence in endemic deer populations
can remain low (Delahay et al., 2007; O’Brien
et al., 2011) and is often highly clustered with
likelihood of infection increasing with age
(O’Brien et al., 2006). Infections are often sub-
acute and chronic, with infected hosts able to
survive for over a decade (Nugent, 2011). How-
ever, some die soon after contracting the infec-
tion with those showing clinical signs (e.g.
weight loss, rough coat, poor body condition)
harbouring a grave prognosis (Griffin and
Buchan, 1994). When tuberculous lesions are
present, the most common sites are the lungs,
the retropharyngeal lymph nodes and thoracic
lymph nodes (Delahay et al., 2002). These lesion
locations suggest the respiratory route is the pri-
mary route of infection, although cutaneous
infection through open wounds is also possible.
While lymphadenitis is often exhibited in
infected deer, with the involvement of at least
one of the lymph nodes, generalized disease in
other organs can also occur (Griffin and Buchan,
1994; Lugton et al., 1998; Griffin and Mackin-
tosh, 2000). For example, in parts of Spain gen-
eralized disease has been observed in over 50%
of cases in some M. bovis outbreaks in red and
fallow deer (Vicente et al., 2006; Martín-
Hernando et al., 2010), and around one-third of
naturally infected white-tailed deer display
lesions in the head and thorax (Fitzgerald and
Kaneene, 2013). In New Zealand’s wild deer
population, generalized M. bovis is relatively
uncommon, with no visible lesions in 25% of
culture-positive deer (Lugton et al., 1998). There
is potential for onward transmission to other
hosts as deer have been found with large, numer-
ous and poorly encapsulated granulomas con-
taining high concentrations of bacilli, and
formation of discharging abscesses associated
with the enlargement of superficial lymph nodes
(Johnson et al., 2008). This is supported by
evidence that naïve deer kept in direct contact
with experimentally infected deer can contract
M. bovis (Palmer et al., 2001). There remains a
potential for transmission between wild and
farmed deer although contact between the two is
thought to be a rare event.
Disease distribution can be affected by cer-
vid social structures. In white-tailed deer,
M. bovis has a heterogeneous distribution as
females are segregated in matrilineal groups
with high site fidelity, and infection levels are