Human-to-Cattle Mycobacterium tuberculosis Complex Transmission in the United States

Area of Science:

• Veterinary Microbiology
• Zoonotic Diseases
• Public Health

Background:

• The Mycobacterium tuberculosis complex (MTBC) causes tuberculosis in humans (TB) and cattle (bTB).
• While bovine TB (bTB) transmission from cattle to humans is well-documented, human-to-cattle MTBC transmission is less recognized.
• Recent reports indicate MTBC transmission from humans to cattle globally.

Purpose of the Study:

• To document and analyze recent cases of human-to-cattle MTBC transmission in the United States.
• To highlight the role of human infections as a source of MTBC in cattle herds.
• To advocate for a One Health approach to manage and prevent MTBC transmission.

Main Methods:

• Case investigation and reporting of three distinct incidents of suspected human-to-cattle MTBC transmission in US dairy settings.
• Whole genome sequencing (WGS) was used to confirm strain relatedness between human and bovine cases.
• Epidemiological analysis to assess the likelihood of human-to-cattle transmission.

Main Results:

• Three probable cases of human-to-cattle MTBC transmission occurred in the US between 2013 and the present.
• WGS confirmed genetic links between MTBC strains in infected dairy employees and cattle in two cases.
• The third case involved a calf infected with M. tuberculosis, with humans suspected as the source, though no infected human was identified.

Conclusions:

• These cases provide strong evidence that humans can transmit MTBC to cattle in the United States.
• Human infections represent a potential source for introducing MTBC into dairy herds.
• A collaborative, multisectoral One Health strategy is crucial for understanding MTBC epidemiology and implementing effective prevention measures.