Bovine tuberculosis

The Pathology and Pathogenesis of Mycobacterium bovis Infection 131

South American camelids

The bacteria from the MTBC can induce exten-
sive pathology in llamas and alpacas. The respi-
ratory system and associated lymph nodes are
the most frequently affected organs. The lung
lesions can be very extensive, affecting more
than 50% of the lung surface (Crawshaw et al.,
2013). The lesions are very caseous with soft,
yellowish creamy material at section. Lesions
often coalesce to form larger granulomas show-
ing cavitations (Garcia-Bocanegra et al., 2010).
Pleurisy is also frequently observed. The lymph
nodes are much enlarged, containing the same
white or yellowish creamy caseous material. His-
tologically, the lesions show large areas of necro-
sis with multiple AFBs within, surrounded by a
rim of inflammatory cells including macro-
phages, neutrophils, lymphocytes and plasma
cells (Fig. 9.13). Other organs, including the
liver, skin, gastrointestinal tract and mammary
gland, can show multifocal lesions (Richey et al.,
2011). The extensive lesions in infected camelids

in the UK, associated with the high within-herd

prevalence of M. bovis-infected animals in some

outbreaks, suggests that these species can be

amplifier hosts and can spread the disease

amongst themselves and possibly to other spe-

cies, including cattle and man (Twomey et al.,

2009). Immunohistochemical characterization

of the lesions has proven to be very difficult due

to the lack of specific reagents and the phyloge-

netic distance of these species to others more

extensively studied, such as cattle. This same

problem exists for wildlife species described in

this chapter.

9.6.2 Wild animals

Several examples occur where a variety of wild

animal species represent major reservoirs of

infection for domestic livestock (Fitzgerald and

Kaneene, 2012). These include cervids in North

America and the Mediterranean basin,

Fig. 9.12. (a) Pyogranulomatous severe panniculitis from a cat naturally infected with M. bovis. (b) Skin
lesion from a cat infected with M. bovis, showing extensive dermatitis and inflammatory cell infiltration in
the subcutis, with disruption of the normal epithelium, close to a fistula. (H&E, 40×) (c) Granulomatous
inflammation within extensive necrotic core within the axillar lymph node. (HE, 40×) (d) Abundant acid-
fast bacilli within the necrotic centre of the lymph node. (Ziehl-Neelsen, 400×; inset, 1000×)