Bovine tuberculosis, caused by Mycobacterium bovis, is known to be a zoonotic disease, capable of transmission into human populations. And while another pathogen, Mycobacterium tuberculosis, causes most cases of tuberculosis (TB) in humans, M. bovis could be involved in more human TB cases than typically estimated, according to research recently reported in The Lancet Infectious Diseases.

Francisco Olea-Popelka, PhD, from Colorado State University, led an international group of researchers representing the World Health Organization (WHO), U.S. Centers for Disease Control, World Organization for Animal Health (OIE), the USDA and others in a meta-analysis of bovine tuberculosis as a cause of disease in humans. As a result of their analysis, the researchers estimate that global health officials fail to detect about 3 million cases of TB each year, many in countries where bovine TB is endemic and where “people live in conditions that favor direct contact with infected animals or animal products.”

Current estimates suggest an annual incidence of about 121,000 cases of zoonotic TB, but the researchers suggest that figure likely is far below the actual incidence.

Estimates of human TB cases caused by M. bovis vary widely. The researchers reported studies finding the incidence of zoonosis as high as 28% and as low as 9% of human TB cases. One study focusing on children in California indicated that up to 45% of TB cases in children were associated with M. bovis, according to an article in International Business Times.

One study, quoted in the report, says 28 percent of all tuberculosis cases are animal tuberculosis cases, while another puts the number at 9 percent. A study that focused on tuberculosis in children said 45 percent of all cases are animal tuberculosis cases.

Studies in Mexico suggest 28% of all tuberculosis cases are down to zoonotic TB but a study in India put the figure at 9% and one in children in California suggested a figure of 45%.

“With approximately nine million individuals contracting TB globally each year, even relatively low percentages of zoonotic TB lead to large numbers of people suffering from this form of the disease,” says researcher Paula Fujiwara from the International Union Against Tuberculosis and Lung Disease in the International Business Times article.  “People living with zoonotic TB require specialized care, but in the vast majority of cases, they are not even adequately diagnosed.”

In their recommendations, the researchers note the WHO goal of ending global TB by 2035, and call on all tuberculosis stakeholders to act to accurately diagnose and treat tuberculosis caused by M. bovis in human beings.

Read more from The Lancet Infectious Diseases