According to the World Health Organization [WHO], Tuberculosis [TB] is the number one cause of death in the world. Approximately 1.7 billion people i.e. one third of the whole world's population are infected with TB bacteria is not suffering from the active disease itself. Each year 8 million of people develop TB and 3 million die. Someone in the world is newly infected with TB every second and one person dies from TB every 10 second.
TB is a bacterial infection that mainly affects the lungs [Pulmonary TB] but can also spread to other organs of the body [Extrapulmonary TB]. The bacteria can invade all proportion of body from skin to any of the internal organs usually by spreading from the lung infection. People of all ages are susceptible to TB; however the elderly, HIV patients and people suffering from malnutrition are at greater risk.
TB can be both Inactive & Active
Inactive TB
[Often referred as Primary Infection] The TB causing bacteria is present in the body, but the patient is not affected by it in anyway and hence unaware of their condition. Primary infection is a state in the development of Tuberculosis but does not always lead to the disease. Only 5 to 10% of the individuals with tuberculosis infection progress to the active TB disease at some stage of their life. A person TB infected cannot spread the infection to others.Active TB
[Often referred as Tuberculosis Disease] Tuberculosis disease develops if the TB causing bacteria becomes active. This may occur immediately after the primary infection in infants, elderly and people with weak immune system. However in most case tuberculosis develops, if does so, long after the person have been infected. A patient with Tuberculosis can spread the infection to others around them.
Causing Agent
Rod-shaped bacteria called tubercle bacilli cause tuberculosis. These bacilli belong to a group of bacteria called Mycobacterium tuberculosis. M. Tuberculosis complex includes 3 other mycobacteria that can cause TB
- M. Bovis
- M. Aficanum
- M. Microti
It is a slow growing, anaerobic [i.e. must intake oxygen to live] bacteria that thrives in areas of the body that are rich in blood and oxygen e.g. lungs.
Transmission
Airborne droplets nuclei expelled when active TB patients cough, sneeze, spit or speak transmit tuberculosis causing bacteria Mycobacterium tuberculosis. Each droplets [5 µm in diameter] containing 1 to 3 tubercle bacilli stays in the air long enough for people around the patient to inhale and become TB infected. Infection may also result from consuming contaminated food or from drinking milk from cattle infected with Mycobacterium bovis bacteria.
Only Pulmonary TB is contagious and can be transmitted when a person with active disease produces aerosol droplets containing Mycobacterium tuberculosis and an otherwise healthy person inhales this air containing bacteria. A person with untreated, active Tuberculosis may infect up to 20 people each year. People with latent/ inactive TB cannot spread the disease.
Extrapulmonary TB cannot be spread easily to others.
The probability of transmission depends upon the following:
- Infectiousness of the patients with TB
- Quantity of bacilli expelled
- Environment of exposure
- Duration of exposure
- Virulence of the patient
At High Risk
People at high risk of TB are those that have:
- HIV
- AIDS
- Malnutrition
- Silicosis
- Diabetes
- End-stage renal disease
- Hematologic disease
- Immunosuppressive therapy
- Intravenous/ illicite drug users
- Alcoholic
Otherwise healthy people under the following condition are also at high risk of acquiring TB:
- Long term care facilities e.g. prison, nursing homes
- Close contact with infectious tubercular individuals
- Health care workers
- Medically underserved
- Low-income population
- High risk racial/ethnic minority population
Host Response
Even though tuberculosis has been one of the leading causes of death for centuries, the understanding of human host response to this infection is in the shadow. However extensive researches show that host immunity plays an important role in the clinical manifestation of tuberculosis and the ultimate outcome of patients.
Once Mycobacterium tuberculosis from the air droplet has reached the lung, there are 4 possible outcomes.
- Initial host response can be completely effect and kill the bacilli successfully and hence the patient has no chance of developing TB at any point their life
- Organism can enter cell can being to grow and reproduce and immediately after infection and hence causing TB disease
- Bacilli may become dormant under the influence of tough scar tissues i.e. become latent TB infection and not harm the patient.
- Latent TB infection at some point can eventually become active hence grows and reproduce resulting in the clinical disease
As a person inhales the bacilli from the air from of them settle into the layer of mucus that lines of the nasal passages and the tracheobronchial tree of respiratory system. These bacilli trapped in the mucus may be moved up the airways towards throat, mouth, and nose and subsequently expelled as sneeze, spit, cough etc. They can also be swallowed and pass through the digestion.
