The Lesions and Diagnosis of BTB in Sudan
In Africa, BTB is widespread in cattle, and it impacts negatively on the animal industry causing economic losses due to carcass condemnation and the imposition of international trade restrictions.
It also poses a serious public health risk (Cosivi et al. 1998; Thoen et al. 2006; Munyeme et al. 2009; OIE 2009).Bovine TB is a neglected, transmissible disease caused by M. bovis. Humans are infected with M. bovis either by inhalation of aerosols or by consuming milk contaminated with the bacteria. Clinically, zoonotic BTB in humans is indistinguishable from that caused by M. tuberculosis (Ocepek et al. 2005; Mathews et al. 2006).
In Sudan, there are limitations, because of financial and infrastructural constraints, in the ability to confirm the diagnosis of BTB in animals. Although routine testing for BTB in cattle using the tuberculin skin test is done occasionally for surveillance purposes, the number of cattle that are tested is limited, and the tests generate insufficient data on which to base assessment of the prevalence of the disease in the country.
Most of the data about the occurrence and prevalence of the disease are obtained from abattoirs (Fig. 20.1) where BTB is diagnosed during the course of meat inspection of slaughtered livestock. The physical appearance of the lesions in animals with BTB in Sudan is similar to that reported elsewhere (Manal et al. 2005; El Tigani et al. 2013), and detection of these lesions is used as a screening mechanism for the presence of the disease in the country (Salih et al. 2010). However, the sensitivity and specificity of this procedure are very low because of the difficulty of distinguishing macroscopically between the various tuberculous-like lesions that can be encountered in livestock and the inability to make a final diagnosis of the specific cause of the disease based on the macroscopical appearance of these lesions. In spite of this, under the current circumstances, it is considered that abattoirs offer an affordable source of information to assess the prevalence of BTB in livestock in Sudan.
The lack of trained laboratory personnel with the ability to detect acid-fast bacteria microscopically is a further impediment. Using microscopy for the detection of acid-fast bacilli is also of limited value, as mycobacteria are difficult, if not impossible, to detect when they occur in low numbers in the smears of the exudate obtained from suspect tuberculous lesions. Many of the specimens contain few bacteria, and these paucibacillary specimens require indirect microscopy to detect the pathogen.
Isolation of M. bovis by culturing is time-consuming, but also in Sudan, it is considered the best method for diagnosing BTB (Hamid et al. 2002; Vincent et al. 2003; Manal et al. 2005; Zackaria et al. 2008; Salih et al. 2010; El Tigani et al. 2013,
2014). Inoculation of guinea pigs and rabbits with suspected M. bovis-infected specimens can also be used to confirm the presence of bovine tubercle bacilli (Awad et al. 1959).
PCR techniques have recently been introduced for diagnosing BTB in Sudan (Taylor et al. 2007), and they have reduced the diagnostic time and increased the sensitivity and specificity of the investigations (El Tigani et al. 2013; Zackaria et al.
2008). Utilization of these techniques should in future generate more reliable data about the presence, distribution, and importance of BTB in the country.
20.3