Chapter 4: Mastery Test 8

Traits and Causes of the World's Deadliest
Infectious Disease: Tuberculosis

     ¹Pan American Health Organization, an office of the World Health Organization (1996), reported that tuberculosis (TB) is the world's deadliest infection. ²TB is deadly due to the traits and rising incidents of the disease. ³TB kills 3 million people (including 300,000 children) each year. ⁴TB currently kills more adults each year than AIDS, malaria, and tropical diseases combined.

      ⁵Approximately one-third of the world's population is infected by the tuberculosis bacterium (Mycobacterium tuberculosis). ⁶Someone in the world is newly infected with TB literally with every tick of the clock, one person per second. ⁷Left untreated, one person with active TB will infect 10 to 15 people in a year's time. ⁸In the next decade, it is estimated that 300 million more people will become infected, that 90 million people will develop the disease, and 30 million people will die from it.

      ⁹The infectious bacteria that causes TB lodges in the lungs and can, in time, spread to the rest of the body. ¹⁰The TB bacilli invade and inflame the respiratory system. ¹¹As a result, fibrous and hardened materials encase the bacilli. ¹²These encased bacilli are called tubercles. ¹³The TB is arrested at this point, not cured. ¹⁴This period of arrest is known as primary tuberculosis.

      ¹⁵When the immune system is weakened, the bacilli become active again and secondary tuberculosis occurs. ¹⁶Then, extensive lesions and cavities occur in the upper portion of the lungs. ¹⁷Over time the following symptoms may develop: persistent coughing, weight loss, fever, night sweats, and spitting up blood (Purtilo, 1978). ¹⁸Persons whose immune systems have been weakened by AIDS, diabetes mellitus, malnutrition, or alcoholism are more open to TB.

      ¹⁹TB is spread through the air and by casual contact. ²⁰When infectious people sneeze, cough, or talk, the TB bacilli in their lungs are expelled into the air where they can remain suspended for hours. ²¹Then, the TB bacilli can be inhaled by others (WHO, 1996). ²²However, only 5-10 percent of people who are infected with TB actually become sick or infectious themselves, because the immune system "walls off" the TB organisms (WHO, 1996).

      ²³Two major factors have contributed to the rise of TB in the United States. ²⁴First, the accelerated spread of human immunodeficiency virus (HIV), which leads to AIDS, increases the possibility of TB infecting the patient because of his or her weakened immune system. ²⁵TB and HIV form a deadly combination, each having an effect on the other.

      ²⁶The second factor is the number of new immigrants and refugees entering the United States. ²⁷The largest number of foreign-born people with TB originated from Mexico, the Philippines, Haiti, India, the People's Republic of China, and Vietnam. ²⁸In 1993, about one- fourth of reported tuberculosis cases were in people who were born outside of the United States.