Diagnosis of Bovine Tuberculosis in Egypt

Accurate detection of infected animals, particularly during the early phases of the disease, is critical for the effective control of BTB. Prompt diagnosis of BTB is important to identify and remove infectious cases, and failure to do so allows ongoing transmission of M.

Several diagnostic tests are used for BTB surveillance in Egypt; some are solely used for research purposes. As reported elsewhere (Bezos et al. 2014), all current BTB diagnostic tests have several limitations that must be taken into account when dealing with the control of the disease.

13.2.1 Tuberculin Skin Test in Cattle

The tuberculin skin test suffers from a lack of sensitivity and specificity, but it is universally accepted as the preferred diagnostic method for BTB in live cattle, and it forms the basis for conducting national test-and-slaughter BTB control programs (Ayele et al. 2004). The test is labor- and time-intensive, as it requires a second inspection of the test animals after 72 h to evaluate the reaction caused by the intradermal injection of PPD.

In Egypt, both the single (SIT), more commonly, and the comparative cervical (CCT) intradermal tuberculin tests are used. For the SIT, 0.1 ml of approved bovine PPD is inoculated intradermally in the mid-neck skin, and after 72 h, the skinfold thickness is measured again. According to the regulations of GOVS, a reaction is considered positive if there is an increase in skin thickness of >4 mm at the injection site; while an increase of al. 2014; Humblet et al. 2011).

The CCT is not routinely used by the GOVS due to financial constraints but researchers and herd owners often fund it privately. The interpretation of the CCT is based on the method of Ovdiennkop et al.

Abou-Eisha et al. (2002) attributed the high prevalence of BTB infection to additional herd-level risk factors such as ever-increasing herd sizes accompanied by an increasing animal density, unhygienic local husbandry practices, and stress induced by intercurrent diseases and by mass vaccination campaigns. Similarly, the high prevalence of mycobacterial infections in pigs was attributed to the poor hygienic standards of pig farming practices in Egypt (Mohamed et al. 2009). Feeding pigs on household and hospital waste as well as refuge from large animal and chicken farms is a common, but risky, practice in Egypt.

13.4.2 Human Intervention Efforts

In Egypt, intradermal tuberculin testing has been performed since 1920, when the prevalence of BTB in the cattle and water buffaloes (Bubalus bubalis) populations was estimated to vary between 2% and 9%, respectively. The prevalence of BTB in cattle and water buffaloes during the 1980s was 6.9% and 26.2%, respectively, although the overall proportion of positive reactors of tested cattle and water buffaloes in 1981, respectively, was 6.2% and 9.4%. However, following the implementation of the national BTB control program in 1981, the prevalence declined to 2.6% during the 1990s (Cosivi et al. 1998) (Table 13.1). Similarly, recent studies demonstrated a declining trend of BTB in certain governorates, including Gharbia and Monufia, where 2.1% and 5.6% tuberculin reactor prevalence was recorded, respectively, in cattle and water buffaloes (Zahran et al. 2014).

13.4.3 Geographical Distribution of BTB in Egypt

The extent of BTB, based on postmortal inspection in abattoirs, varies substantially between regions in Egypt (Table 13.1). The data are often unreliable as most of the abattoirs in Egypt lack diagnostic facilities to rapidly confirm the presence of M. bovis in exudates collected from tuberculous-like lesions detected during routine meat inspection. The available data indicate that BTB is much more prevalent in the Egyptian Nile Delta and Valley compared to the rest of the country, probably because these regions where rural communities consist of smallholder families that traditionally own a few domestic stock, are the most densely populated areas in Egypt. Additionally, some of the people living in these areas keep animals inside their houses, which creates a major zoonotic BTB health risk. The prevalence of BTB in cattle was also high in other governorates such as Alexandria (6%), and in Dakahlia and Behera (9.6% and 14.1%, respectively) (GOVS 1992). In contrast, low prevalences were recorded at El-Basateen Abattoir, Cairo (0.21%), and the Ismailia Abattoir (0.6%). The underlying causes of the marked wide geographic variation in the prevalence of BTB in Egypt are poorly understood.

In recent years, the proportion of positive reactor cattle in some governorates increased sharply: in Port Said, the prevalence increased from 11.8% in 1990, to 15.9% in 1991; in Behera from 2.7% in 1990, to 13.4% in 1991; and in Dakahlia from 0.4% in 1989, to 23.4% in 1991. Fluctuations in the number of tuberculosis­like lesions detected in cattle slaughtered in Egyptian abattoirs could be ascribed to circumstances governing the volumes of slaughter such as religious feasts and other socio-cultural events when more cattle are slaughtered than normally.

13.4.3.1 Animal-Level BTB Risk Factors in Egypt

In Egypt, BTB affects cattle, camels, water buffaloes, sheep, and pigs (Table 13.1).

Other strains of the MTC (including M. tuberculosis), and Mycobacterium spp. belonging to the MOTT group (including M. avium, M. chelonae, M. porcinum, M. gallinarum, M. simiae, and M. scrofulaceum), and other genera (such as Rhodococcus equi) have been isolated from tuberculous lesions in Egypt. This situation complicates epidemiological surveillance and dealing with the complexity of zoonotic TB as a public health risk, and it emphasizes the need to accurately identify the specific pathogenic mycobacteria from clinical specimens.

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