Tuberculosis Disease & the BCG Vaccine
By Yosef Kebede
Ethiopian Review, August 1996
Mycobacterium Tuberculosis (TB) is one of the most common communicable diseases that is spread from person to person through the inhalation of the TB bacteria. TB usually affects the lungs, but it can also affect other parts of the body. During the late stages of this disease it can affect the brain, kidney and the spine. TB is put into the air when a person with active TB disease of the lungs or throat coughs or sneezes. If a person inhales the air that contains the TB bacteria, he or she may become infected.
Initially, people with TB infection do not feel sick or have any symptoms. Within the first two weeks of infection the, TB bacteria travels into the lungs and, most commonly, into the lower portion or lobes of the lung. A normal inflammatory response occurs, but the TB bacteria is not destroyed. Some of the bacteria are engulfed by alveolar macrophages (a type of white blood cell that “eats” invading disease organisms) and drain into local lymph nodes. In the lymph nodes the bacteria antigens (a substance responsible for producing a specific antibody to fight infection) are presented to what are called antigen specific helper T-cells, which are part of the body’s immune system. These activated T-cells then circulate through the body. It is at this point that an individual will have what is called a “Positive PPD Skin Test.”
When the T-cell is activated to fight the TB bacteria in the lungs, it releases what is called the chemotactic factor, which is a substance used to recruit monocytes (white blood cells that develop macrophages). When the monocytes are activated, they form what are called granulomas or tumors. It is the granulomas that seal off the TB bacteria, making it impossible for the body to kill them. The TB bacteria can remain viable or alive inside a person’s body for decades within a granuloma. Because of this, a person can experience what is called a “reactivation” which happens when a TB outbreak occurs later in life.
The general symptoms of TB infection include fever, chills, night sweats, fatigue, loss of appetite, and weight loss. I would like to caution that just because you might have some of these symptoms, it does not mean that you have TB. It could be an indication of other diseases. Only a qualified physician or health care provider can make an accurate diagnosis. Symptoms of TB infection of the lungs may also include a productive and/or prolonged cough and chest pain. Because of TB’s high communicable potential, the Center for Disease Control (CDC), a U.S. agency responsible for stopping the spread of diseases, recommends screenings for TB for the following high risk groups:
*Health care workers
*Persons with HIV infection
*Persons who inject drugs
*Foreign-born individuals from countries where TB is common
*Medically under-served, low income populations
*Residents of long term facilities such as nursing homes and jails
*Persons who have Diabetes, Malnutrition, Immunosuppressed patients, Gasrectomy, End stage renal disease, and Siulicosis, which can increase their risk of TB:
If an individual has a positive result for Mantoux or Tuberculin skin test, he or she should be evaluated by a physician and chest x-ray, sputum smear, and culture tests should be done in order to confirm the diagnosis.
The Bacilli Calmette-Guerin (BCG) vaccine is widely used in many countries, but it is not widely used in the U.S. There are two reasons for this. First, several studies have shown that the BCG vaccine varies in its effectiveness from 0% to 76%. The second reason is that the actual BCG vaccine may cause a positive reaction to the skin test. This is one of the concerns that many Ethiopians have. Most Ethiopians who are not American born have had the BCG vaccine, and therefore when they are being screened for TB, they may have a positive TB skin test result.
In persons who have been vaccinated with BCG it is impossible to determine whether a positive tuberculin skin test reaction is caused either by the immunization with BCG or by an actual infection with the TB bacteria. The probability that an individual will have a positive reaction is further increased by the following factors:
*If the size of the TB skin test (on the arm) increases
*The length of time between vaccination and the skin test increases
*An individual comes in contact with a person who has “active” TB
*There is a family history of TB
*The individual is from a country where TB is common
A positive result from a TB screening complicates things as far as what diagnosis or treatment should be given by the physician, including what type of preventative therapy should be conducted. My recommendation is that any individual who has had a positive TB skin test should only have a chest x-ray done every year or every two years, depending on exposure, for example, working in a hospital setting and nursing home.
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Yosef Kebede, M.D., works with Concerned Medical & Health Care Professionals, Inc., Silver Spring, MD. The article is presented on the request of Yeharer Gashaw.