Bovine tuberculosis

130 F.J. Salguero

9.6 Comparative Pathology of

M. bovis Infection in Other Domestic

and Wildlife Species

The range of hosts susceptible to M. bovis is very
broad and includes humans, domestic and wild
ruminants, swine and carnivores (Palmer et al.,
2015).

9.6.1 Domestic animals

Small ruminants

M. bovis infection in sheep and goats is closely
related to tuberculosis in cattle in terms of
immunological responses and pathological
characteristics (Marianelli et al., 2010; Bezos
et al., 2011; Domingo et al., 2014). Tuberculosis
in small ruminants is primarily a chronic infec-
tion causing exudative granulomatous caseous
inflammatory lesions in the lungs and associ-
ated lymph nodes, although lesions can also
occur in the upper respiratory tract (Domingo
et al., 2014). Generalized forms affecting other
organs such as the spleen, liver and kidneys are
infrequent (Daniel et al., 2009). Goats can
develop liquefactive necrosis with the formation
of cavernous lesions, similarly to human tuber-
culosis, making this animal a good experimental
model of the human disease (Marianelli et al.,
2010; Gonzalez-Juarrero et al., 2013).

Companion animals (dogs, cats and horses)

There are few data on the prevalence of tubercu-

losis in dogs and cats worldwide. Depending on

the route of infection, the lesions will be local-

ized in the respiratory, gastrointestinal or integ-

umentary system (Gunn-Moore et al., 2010).

Historically, cats were usually infected by drink-

ing contaminated milk, while dogs were infected

by aerosol from infected owners (Jennings,

1949). Dogs typically start with lesions in the

lungs, but they disseminate quickly. The most

common form of tuberculosis in cats is the cuta-

neous form, with respiratory and gastrointesti-

nal forms less frequently observed (Gunn-Moore

et al., 2010, 2011; Rufenacht et al., 2011). This

cutaneous form probably arises from infected

bite wounds, local spread, haematogenous dis-

semination to the skin or even contaminated

surgical wounds (Jennings, 1949; Gunn-Moore

et al., 2010; Roberts et al., 2014; Murray et al.,

2015). The lesions are typically firm, raised der-

mal nodules with ulceration with draining sinus

tracts and subcutaneous tissue inflammation

(Gunn-Moore et al., 2011; Rufenacht et al.,

2011) (Fig. 9.12). The skin lesions are often

associated with localized or generalized granulo-

matous lymphadenitis. The infection can dis-

seminate to the lung from the skin site inducing

a typical haematogenous interstitial pneumo-

nia. Pleurisy and pericardial effusion are also

common in animals with respiratory infection

(Snider, 1971). Histologically, the lesions are

typical multifocal to coalescing granulomas

composed of multiple macrophages and epitheli-

oid cells. MNGCs are very uncommon and neu-

trophils are often observed in large numbers,

mostly due to secondary infections in the skin

lesions. In general, the lesions are less prone to

encapsulate and mineralization is very rare. The

number of AFBs is quite low with some excep-

tions (Fig. 9.12).

The digestive route of infection is the most

common in the horse, with lesions frequently

found in head and neck lymph nodes, the gastro-

intestinal tract and the mesenteric lymph nodes.

The lesions are often disseminated with miliary

inflammation in the liver, spleen and lungs. The

lesions in the horse are typically proliferative

and less caseous than in cattle. Mineralization is

very rare and the lesions can be mistaken for

neoplastic masses (Domingo et al., 2014).

Fig. 9.11. Multifocal granulomas within the lung
of a guinea pig infected with M. tuberculosis. The
granulomas are in different stages of development
showing solid lesions with no necrosis (small) and
extensive necrosis and fibrotic capsule (large).
(H&E, 20×)