Bovine tuberculosis

132 F.J. Salguero

mustelids in the British Isles, swine in southern
Europe, marsupials in New Zealand and bovids
in Africa (see Chapter 6). The pathology and
pathogenesis of M. bovis infection in these spe-
cies have been studied with some limitations due
to the lack of reagents and reduced number of
experimental studies.

Eurasian badgers

The Eurasian badger (Meles meles) is an impor-
tant wildlife reservoir of bovine tuberculosis in
the UK and the Republic of Ireland (Chambers
et al., 2017), and their role in the maintenance
and spread of the disease is a matter of consider-
able scientific, political and public interest
(Brooks-Pollock et al., 2014). Badgers infected
with M. bovis have been also found in other
countries in continental Europe (Sobrino et al.,
2008). The pathology associated with tubercu-
losis in badgers is centred on the respiratory sys-
tem, with more than 50% of the lesions restricted
to the lungs and 35% of the badgers showing
lymph node involvements (Gallagher and
Clifton-Hadley, 2000). The pulmonary lesions
are variable, typically caseous granulomas
showing different sizes from large nodules
and lobar pneumonia to disseminated miliary
lesions. The lesions in the lymph nodes are
typical of a granulomatous lymphadenitis, with
yellowish areas with enlarged and oedematous
granulomas. Very rarely, the lesions will develop
mineralization. Lesions can also be found in the
kidneys resulting in elongated radial lesions,

liver or spleen, as pale sawdust-like and dissemi-

nated (Fitzgerald and Kaneene, 2012). Badgers

appear to have a containment phase of the dis-

ease, similarly to latency in humans, which can

last for years (Gallagher and Clifton-Hadley,

2000). In contrast, many badgers show no visi-

ble (gross) lesions (NVL) with positive bacterial

culture from either the lung or lymph nodes,

making the diagnosis and epidemiology of the

disease more complicated. Histologically, the

granulomas are solid, composed mainly of epi-

thelioid macrophages with fewer lymphocytes,

no apparent MNGCs (Fig. 9.14) and with limited

areas of necrosis (Corner et al., 2011). Badgers

can also be infected with non-tuberculous myco-

bacteria, nematodes or fungal adiaspiromycosis,

inducing granulomatous lesions in the lung.

Cervids

White-tail deer are a cervid species heavily

involved in the epidemiology of M. bovis infec-

tion in the US. The typical gross pathology in this

species consists of multiple caseous granulomas

with purulent centres in affected lungs or lymph

nodes. The caseous centre is normally very

soft and can resemble abscesses (Fitzgerald

and Kaneene, 2012). The typical lymph node

affected is the medial retropharyngeal frequently

with other tissues involved. The thoracic lesions

normally consist of multiple pulmonary granu-

lomas disseminated throughout the lung paren-

chyma and often extending to the parietal and

visceral pleura (Fitzgerald and Kaneene, 2012).

Fig. 9.13. (a) Detail of the outer layer of a granuloma from the mesenteric lymph node of an alpaca
infected with M. bovis. The necrotic area (upper part of Fig) is surrounded by abundant inflammatory
infiltrate, mostly composed of lymphocytes, a few macrophages and no multi-nucleated giant cells.
(inset) Extensive necrotic core of the lesion. (H&E, 200×; inset 20×) (b) Few acid-fast bacilli (arrows)
are observed within the necrotic centre of the lymph node. (Ziehl-Neelsen, 600×)