UNIVERSITY PARK, Pa. — The number of human tuberculosis (TB) cases that are due to transmission from animals, as opposed to human-to-human transmission, may be much higher than previously estimated, according to an international team of researchers. The results could have implications for epidemiological studies and public health interventions.
“Tuberculosis kills 1.4 million people every year, making it the most deadly disease arising from a single infectious agent,” said Vivek Kapur, professor of microbiology and infectious diseases and Huck Distinguished Chair in Global Health, Penn State. “India has the largest burden of human tuberculosis globally, with more than 2.6 million cases and 400,000 deaths reported in 2019. Additionally, the cattle population in India exceeds 300 million, and nearly 22 million of these were estimated to be infected with TB in 2017."
Kapur noted that the World Health Organization, World Organisation for Animal Health, and Food and Agriculture Organization of the United Nations define zoonotic TB as human infection with Mycobacterium bovis, a member of the Mycobacterium tuberculosis complex (MTBC).
To evaluate the use of M. bovis as a proxy for zoonotic tuberculosis and to investigate the potential role of other MTBC subspecies, Kapur and his colleagues analyzed 940 bacterial samples — both pulmonary (from lung fluid or tissue) and extrapulmonary (from tissues other than the lungs) — collected from patients who were visiting a large reference hospital for TB in southern India. The researchers used PCR to speciate M. tuberculosis complex organisms and then sequenced all the non-M. tuberculosis samples. Next, they compared the sequences to 715 sequences from cattle and humans that had previously been collected in south Asia and submitted to public databases.