Tuberculosis by Proxy

The number of human tuberculosis cases 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."

Kapur noted that zoonotic tuberculosis is defined 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 investigate the potential role of other MTBC subspecies, Kapur and his colleagues analyzed 940 bacterial samples collected from patients who were visiting a large reference hospital for tuberculosis in southern India. They used PCR to speciate the MTBC 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. Their findings were published in The Lancet Microbe.

"Our findings suggest that M. Bovis might be uncommon in India, and that its detection may not be an adequate proxy for zoonotic tuberculosis infection in humans," said Sreenidhi Srinivasan, postdoctoral scholar in the Huck Institutes of the Life Sciences. "These data indicate that members of the tuberculosis complex other than M. Bovis might be more prevalent in livestock in India."

--Sara LaJeunesse