A Test to Combat Bovine Tuberculosis

Scientists at Aberystwyth University (United Kingdom) have developed two diagnostic tests for bovine tuberculosis. These tests could help distinguish between infected animals and those vaccinated against the disease, marking a significant advance in the fight against this deadly zoonosis.   Bovine tuberculosis is a chronic infectious disease transmissible to humans, caused by Mycobacterium bovis, a mycobacterium closely related to the one responsible for human and avian tuberculosis. M. bovis can infect many domestic and wild species, particularly cattle and deer, but also wild boars, badgers, and foxes. The name “tuberculosis” comes from the caseous nodules called “tubercles” that form, in particular, in the lymph nodes of affected animals. The disease causes a deterioration in overall health, weight loss, and coughing, and ultimately leads to death. In cattle, the infection is often asymptomatic, with clinical signs appearing only late in the course of a disease that is generally very protracted. However, even if they do not develop the disease, infected animals may experience reduced productivity. Until the 1920s, when control measures were introduced in developed countries, tuberculosis was one of the major diseases affecting domestic animals worldwide. Today, it remains a significant disease in cattle and wild animals, as well as a major zoonosis. Outbreaks of bovine tuberculosis must be reported to the World Organisation for Animal Health (WOAH), in accordance with the Terrestrial Animal Health Code. Since 2001, France has been considered officially free of bovine tuberculosis, despite the persistence of about 100 outbreaks each year in cattle herds. To reach this stage, numerous measures have been implemented to combat this infection. The eradication of tuberculosis relies primarily on screening for the disease and the culling of infected animals. Treatment of infected animals is rarely carried out due to its high cost, the length of time required, and the more ambitious goal of eradicating the disease. As for vaccination, it is practiced in human medicine (BCG) but is rarely used as a preventive measure in animals. In fact, the vaccines currently available for veterinary use vary in effectiveness. This incomplete vaccination coverage hinders efforts to completely eliminate the disease. For this reason, the vaccine has remained largely unused in cattle and is banned throughout the European Union, as well as in the United States and many other countries. However, this health policy could be reconsidered thanks to two tests developed by researchers from Ethiopia, India, the Netherlands, the United Kingdom, and the United States, based on discoveries made by scientists at the University of Aberystwyth. They have developed skin tests capable of distinguishing animals vaccinated against bovine tuberculosis from those infected with the bacteria. This is the culmination of more than twenty years of work on developing vaccines and diagnostic tests to control this disease. Field trials are still underway in the United Kingdom and India, but scientists say that the ability to distinguish between vaccinated and infected animals will facilitate the implementation of vaccination programs on a global scale. Without this distinction between positive animals (infected or vaccinated), it is impossible to carry out widespread vaccination alongside traditional strategies for screening, disease control, and culling. Nor can vaccine efficacy and disease prevalence be effectively monitored in vaccinated animals. Without these tests, vaccination strategies cannot function alongside existing tuberculosis control systems. They therefore represent new hope for strengthening the fight against this deadly zoonosis.