Mycobacterium bovis Infection in Humans in Egypt

Four percent of the TB cases in the WHO’s Eastern Mediterranean Region compris­ing 22 countries occurs in Egypt. Generally, countries of the Eastern Mediterranean Region fall into three distinct epidemiological categories, Egypt being a middle­burden country, clustered with other countries with an estimated prevalence of 25-49 TB cases (all forms) per 100,000 of the population.

Generally, the proportion of TB caused by M. bovis in humans is relatively low compared to M. tuberculosis, but it has become increasingly more prevalent in human populations subject to poverty, malnutrition, infection with the HIV, and inadequate health care (Michel et al. 2010). In the developing world, M. bovis infection is responsible for 5-10% of human TB cases, but this varies between countries (Haddad et al. 2004). The relatively low rate of M. bovis infection in humans in developing countries (in Africa and elsewhere) could probably be attrib­uted to the lack of adequate diagnostic facilities and tests, as those that are used do not allow differentiation between the different species of mycobacteria. In addition, accurate diagnosis is difficult even when culture facilities are available, as M. bovis grows poorly on the standard Lowenstein-Jensen medium containing glycerol, which is one of the most widely used culture media for M. tuberculosis (Collins and Grange 1983).

In Egypt, the estimate of the number of human TB cases caused by M. bovis is inaccurate, mainly because of the difficulties in acquiring data from various Egyptian governorates, the lack of computerized patient record systems, and the vastness of some of the governorates.

It appears that the risk of humans contracting M. bovis in Egypt has decreased during the last several decades (El Ibiary et al. 1999). Human M. bovis infection in Egypt, of which approximately 63% of these patients were from rural areas (FAO 1993), accounted for 12.2% of the total number of human TB cases in 1953. The number declined to 10.0% in 1969, and to 5.4% in 1980 (Cosivi et al. 1998). In a recent investigation, 9 of 20 randomly selected samples from patients with abdom­inal TB were found to contain M. bovis (Nafeh et al. 1992). In another study 5% of 300 mycobacteria cultured from human sputum were M. bovis (El-Sabban et al. 1995). Most of these patients lived in the vicinity of the abattoir in Cairo, and some were workers at the abattoir. In addition, M. bovis has been identified in the cerebrospinal fluid of a patient suffering from tuberculous meningitis (Cooksey et al. 2002).

The isolation of M. bovis from milk and sputum samples collected from tuber­culin test-positive cows (El-Olemy et al. 1985) indicates that cattle with BTB excrete M. bovis in milk or sputum and that they play a critical role in the transmission of zoonotic TB. Humans are also exposed to pigs with BTB; M. bovis was isolated from 12 of 66 swine carcasses containing TB-like lesions (Mohammed et al. 2009). The lack of awareness about the risk of infection and the modes of transmission of M. bovis predispose abattoir workers and the general public to the risk of contracting zoonotic TB (Ibrahim et al. 2012).

Given the high prevalence of BTB in cattle and its presence in other species, there is a need for comprehensive disease surveillance with an emphasis on the high-risk populations, to adequately determine the extent of zoonotic TB in Egypt. Due to the known existing high risk, however, effective measures should be instituted immediately to control the disease in farm animals and to advocate the application of heat treatment of milk and other animal products. Regular health inspection of abattoir workers and implementation of public awareness programs are further important steps that must be taken to curtail the risk of occupational zoonotic TB infections.

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