What is the most common route of infection for Mycobacterium tuberculosis and M. bovis?

• A. The fecal-oral route
• B. Contaminated needles or other instruments
• C. Aerosol inhalation
• D. Skin lesions

Answer: (C)

The main way these bacteria spread is through the air. When someone with active TB coughs, sneezes, talks, or sings, they release tiny droplets that contain the organisms. These droplets can evaporate into even smaller particles called droplet nuclei that stay suspended in the air and can be inhaled by others. Once inhaled, the bacteria reach the lungs, are taken up by macrophages, and can establish infection, leading to TB disease. For Mycobacterium bovis, ingestion of contaminated dairy products can also cause infection, but inhalation of aerosols remains the most common route for new infections. Other routes like fecal-oral exposure, contaminated needles, or skin lesions are not typical for transmitting these bacteria.