Tuberculosis is a highly infectious disease of the lungs transmitted via aerosols. An aerosol in this instance will be caused by sneezing and coughing both of which produce small water droplets in which are carried living bacterial cells.
The cause of tuberculosis is the bacterium Mycobacterium tuberculosis. Infected water droplets ejected by a sneeze or cough from a person with the active pulmonary infection, are inhaled by another person who breathes in and retains the bacterial cells.
This is known as the Primary Infection.
The result is an infected individual who may or may not present symptoms of the disease to themself or to doctors. However, the bacteria cause tubercles in the lungs; these are localised collections (aggregates) of bacterial cells.
Although the individual may not know they are infected, their sensitivity is increased to the bacteria and the bacterium's metabolic products (hypersensitivity). A simple diagnostic test called unsurprisingly the Tuberculin Test will identify how great the hypersensitivity is.
The tuberculin test involves injecting a product of the bacteria's metabolism into the skin; a localised immune reaction will occur a few days later. A reddened, raised, hardened area appears at the site of the injection indicating that at some time the person has been exposed to the bacterium.
The person's medical records would show that they are tuberculin positive.
A person who is tuberculin positive can present the worst symptoms of tuberculosis when the dormant bacteria become active again. This time, the disease would be identified by doctors as called postprimary tuberculosis infection. What causes this re-activity?
- Stress, overcrowding, malnutrition (poor, inadequate diet) and hormonal imbalance can provide the conditions that are ideal for a repeated pulmonary infection.
Global distribution of TB. Note and consider carefully what the relationship might be between the incidence of TB and regions shown in green.
Postprimary symptoms are serious and severe damage is caused to the lungs. Lesions occur which means that sections of lung are effectively 'dead'. When extensive tissue destruction has occurred, live bacterial cells can be found in the sputum of the individual.
Thus the cycle of infection can continue when such persons sneeze and cough as they will invariably do due to the terrible damage to the lungs.
