Zoonotic tuberculosis revealed with a new molecular test
With 1.6 million annual deaths worldwide, tuberculosis (TB) is the leading cause of death from an infectious disease. Infections from animal origins are largely ignored in many countries because of the lack of specific identification of the bacterium involved by standard diagnostic tests. A new study shows unsuspected prevalence of these zoonotic infections in patients in the Middle East, revealed by a new generation of molecular test. This work, conducted in collaboration with the Lebanese University, was published in The European Respiratory Journal.
The World Health Organization (WHO), the Food and Agriculture Organization of the United Nations and other international organizations have called for reinforced global assessment of zoonotic TB in humans, caused by the bacterium Mycobacterium bovis. Its overall contribution to human TB, otherwise mainly due to Mycobacterium tuberculosis, may be underestimated, particularly on the continents with the highest presumed burden, that is, in Africa and Asia.
This study highlights a previously unsuspected prevalence of M. bovis infections in patients with TB in the Middle East. M. bovis frequently causes extrapulmonary TB, which is difficult to diagnose. In addition, this bacterium is naturally resistant to pyrazinamide, an antibiotic essential for the standard short-course TB treatment. The most commonly used diagnostic tests endorsed by WHO do not detect this resistance and do not differentiate M. bovis from M. tuberculosis. Patients infected with M. bovis may therefore be inadequately treated, with a potentially negative impact on the treatment outcome. Under-diagnosis in humans also implies the undetected existence of infected animals and contaminated foods, such as unpasteurized dairy products or undercooked meat, representing risks of zoonoses escaping from usual TB control measures.
This work shows the existence of multiple cases of TB caused by M. bovis, in a study covering all patients reported to the TB control program in Lebanon over a period of 18 months. These cases were revealed by a new molecular test, called Deeplex®-Myc-TB, developed by Genoscreen in collaboration with P. Supply. Unlike standard tests, this test is able to differentiate M. bovis from M. tuberculosis, and simultaneously detects resistance to pyrazinamide, as well as to twelve other antibiotics/classes of antibiotics, through the analysis of a large panel of target genes of these bacteria. These results can be obtained in just one to three days, instead of weeks required for testing based on culture.
The use of this test will therefore help better detect such zoonotic cases, as well as the multidrug resistance of many other strains of TB, allowing a much faster and more appropriate definition of patients treatments, and a better detection of origins of infection.
Identification of a M. bovis strain of tuberculosis isolated from a tuberculosis patient in Lebanon with the Deeplex-Myc-TB® assay. The red section indicate a mutation specific to M. bovis conferring resistance to pyrazinamide. Molecular typing information identifying the strain is shown in the center.
For more details :
Zoonotic tuberculosis in humans assessed by next-generation sequencing: an 18-month nationwide study in Lebanon.
El Achkar S, Demanche C, Osman M, Rafei R, Ismail MB, Gaudin C, Duthoy S, De Matos F, Yaacoub H, Pinçon C, Hamze M, Supply P.
Eur Respir J. 2019 Sep 26. pii: 1900513. doi: 10.1183/13993003.00513-2019. [Epub ahead of print] No abstract