Bovine tuberculosis

The Pathology and Pathogenesis of Mycobacterium bovis Infection 133

Microscopically, the pulmonary and lymphoid
granulomas are typical caseous lesions with an
outer layer of lymphocytes, histiocytes and
MNGCs surrounding a necrotic core that may
contain large areas of mineralization (Fitzgerald
and Kaneene, 2012).
The role of wild cervids as reservoirs of
tuberculosis in some regions of Spain has also
been described (Gortazar et al., 2003; Aranaz
et al., 2004; Hermoso de Mendoza et al., 2006).
In fallow deer, we have observed a high preva-
lence of tuberculosis with animals showing
parynchematous caseous lung lesions varying
from 1–10 cm in diameter, often coalescing
(Fig. 9.15). Generalized disease is frequent with
large and encapsulated granulomas similar to
abscesses in lymph nodes of variable size, some-
times up to 20 cm, and containing creamy yel-
lowish caseous material (García-Jiménez et al.,
2012). The number of AFBs within the lesions is
far greater than those observed in cattle with
tuberculosis (Martin-Hernando et al., 2010;
García-Jiménez et al., 2012). Red and fallow deer
show the largest number of poorly encapsulated
granulomas often containing many hundreds of
bacilli (De Lisle et al., 2002; Johnson et al., 2008;
Martin-Hernando et al., 2010; García-Jiménez
et al., 2012). The presence of these poorly
encapsulated granulomas has been pointed
out as a potential source of environmental

contamination from deer species in the British

Isles and onward transmission to other animal

species (Johnson et al., 2008).

The characteristic cellular composition of

early stage granulomas is associated with an ini-

tial immune response from the host. The major-

ity of cells in these granulomas are macrophages

and T lymphocytes. Interestingly, stage I and II

granulomas express high levels of IFN-γ (García-

Jiménez et al., 2012) associated with an early

Th1 response by the host and positively corre-

lated with an increase in pathogenicity in

M. bovis infection in cattle (Villarreal-Ramos

et al., 2003). The presence of abundant B cells in

the outer layers of late-stage granulomas, form-

ing nests similar to those observed in cattle,

might contribute to the coordination of host

immune responses with the CD3+ T cells (Ulrichs

et al., 2004).

Wild boar

Several wild ungulate species contribute to

M. bovis infection maintenance in a multi-host

system in the Mediterranean habitat of south-

ern Europe, but wild boar is the single most

important reservoir in these regions (Hermoso

de Mendoza et al., 2006; García-Jiménez et al.,

2013a). The typical macroscopic lesion pattern

in wild boar with tuberculosis are characterized

by localized and delimited granulomas in the

head lymph nodes (Fig. 9.16) and rare general-

izations (Bollo et al., 2000; Zanella et al., 2008).

Fig. 9.14. Multifocal granulomas at different
stage of development in a badger infected with
M. bovis. Some of the lesions are small and
solid, while other show a central area of necrosis
surrounded by a rim of epithelioid cells, no multi-
nucleated giant cells and lymphocytes at the outer
layers of the lesion. No evident capsule can be
identified. (H&E, 40×)

Fig. 9.15. Large coalescent caseous granulomas

in the lung of a fallow deer infected with M. bovis.

Yellowish creamy material can be observed within

the lesion. Courtesy of ‘Red de Recursos Faunisti-

cos’ group, University of Extremadura, Spain.