Bovine Tuberculosis in Other Domestic Species 85
about 27 million camels globally, 80% of which
are dromedary and 20% are Bactrian camels
(Food and Agriculture Organization, 2012). The
latter exclusively occupy the cold deserts of Asia.
Camels are working animals that are used as
pack animals or for riding, and to contribute
milk, fibre, hides, draught power and meat to the
livelihoods of agro-pastoral communities in
Africa and Asia (Wardeh, 2004). The drome-
dary camel is also bred for camel racing and
there is a growing feral population of about
one million dromedary camels in Australia
(Schwartz, 2013). In Africa, especially in Sahel
countries and East Africa, camel populations
make a significant contribution to national
economies and bear an unutilized economic
potential (Farah, 2004). In sub-Saharan Africa,
camels contribute 7% of total milk production
while the highest numbers of dairy cattle are
found in Somalia, Mali, Ethiopia and Niger
where they contribute to food security (Food and
Agriculture Organization, 2017).
Camels are susceptible to members of the
MTBC, of which M. bovis is the most frequently
reported causative agent of camel tuberculosis.
The disease has long been recognized and can be
fatal, but appears to have a rare occurrence in
nomadic camels (Fassi-Fehri, 1987; Kinne et al.,
2006; Wernery et al., 2014). In a review of
tuberculosis in camels Mason (1917) described
its sporadic occurrence in India, Sudan and
Algeria, and a much more widespread distribu-
tion of the disease in Egypt since the late 19th
century (Littlewood, 1888, cited in Mason,
1917). In 1987, Mustafa briefly reviewed the lit-
erature and concluded that tuberculosis in cam-
els may be exacerbated under intensive farming
conditions and when farmed and housed in close
contact with cattle (Mustafa, 1987). Under
these circumstances isolation of M. bovis from
bulk camel milk was reported in Russia
( Donchenko et al., 1975, cited in Mustafa,
1987). In 2008, Manal and Gobran investigated
a total of 704 camels slaughtered at different
abattoirs in Egypt. The animals originated from
farms with and without cattle, and tuberculosis
was only confirmed in camels at a prevalence of
0.7% from farms co-inhabited by cattle (Manal
and Gobran, 2008).
Although tuberculosis is today considered
of increasing socio-economic and public health
importance (see Chapter 2 for details), there is a
large paucity of prevalence and epidemiological
data from most camel-breeding countries. It is
unknown whether this is due to a lack of report-
ing or to the absence of the disease. Somalia has
the largest camel population in Africa, followed
by Mali, yet less than half a dozen reports, which
only marginally mention tuberculosis in Soma-
lia, could be traced (Abdurahman and Bornstein,
1991). Sporadic studies reported the presence of
M. bovis in camels in Niger (Boukary et al.,
2012), Nigeria (Bala et al., 2011; Abubakar
et al., 2012), Mauritania (Chartier et al., 1991),
Egypt, Ethiopia, India and Pakistan. In Eritrea,
tuberculosis in camels is infrequently encoun-
tered, but in a recent survey among 198 drome-
dary camels using the single comparative
intradermal tuberculin test (SCITT) a prevalence
of 1.5% was observed (Ghebremariam, M.K.,
personal communication). When a lower cut-off
was applied, as previously suggested for cattle,
the prevalence increased almost eightfold to
11.6%. As shown by other investigators, the
SCITT appears to be prone to false positive reac-
tions and of doubtful diagnostic value in camels,
possibly due the high rate of infections with
non-tuberculous mycobacteria. The lower SCITT
cut-off may therefore have to be used with cau-
tion (Bush et al., 1990; Wernery et al., 2007;
Alvarez et al., 2012). The few detailed reports on
diagnostic assays in Old Word camelids were
reviewed by Alvarez who cited the findings by
Schillinger (1987) according to which between
10% and 20% false positive skin test reactions
were observed in Australian dromedaries with a
tuberculosis free status (Alvarez et al., 2012).
Bush et al. (1990), on the other hand, found that
the SCITT also failed to detect M. bovis infection
in two Bactrian camels, one of which exhibited
localized and the other one generalized tubercu-
losis (Bush et al., 1990). The SCITT forms the
basis for tuberculosis testing in many animal
species but appears unsuitable for screening or
control in camels (Wernery et al., 2014).
Infectious conditions of the lungs were
reported in 10% of slaughter camels (Zubair
et al., 2004). Tuberculosis-like lesions in the
respiratory tract of camels can, apart from
M. bovis, be associated with non-tuberculous
mycobacteria including M. kansasii, M. fortui-
tum, M. smegmatis or Rhodococcus equi
( Elmossalami et al., 1971; Kinne et al., 2011). As
a consequence, prevalence data based on the