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Tuberculosis Is Airborne

We begin our examples of disease transmission with tuberculosis. In industrialized nations, tuberculosis serves as an example of successful infection control; in some developing countries it illustrates the consequences of failure.

When Mycobacterium tuberculosis (see Figure 7-1) gets deep inside a person’s lungs, human scavenger cells called macrophages engulf it. These amoeba-like cells normally protect us from disease by killing pathogens, but M. tuberculosis survives. For reasons that are poorly understood, about 90% of infected persons, if otherwise healthy, either clear infection or drive M. tuberculosis into a dormant state. In the dormant state, M. tuberculosis can remain hidden for decades, ready to resume reproduction when the infected person’s immune system is impaired. If the bacteria fail to shift into the dormant state or when they come out of it, they reproduce. Eventually, they create cavities in the patients’ lungs. Patients with active tuberculosis have a persistent cough; sometimes they cough blood and lose weight as they are consumed by the bacteria. (For centuries, tuberculosis has been called consumption.) Death frequently follows if antibiotic treatment is unavailable. (The death rate is about 50% for immune-competent patients.)


  

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