Tuberculosis (TB for short) is a communicable disease caused by the organism called Mycobacterium Tuberculosis.
It usually attacks the lungs, causing Pulmonary(Lung) TB. But it can attack other parts of the body like the spine, brain, kidneys etc.
The organism is an aerobic organism as oxygen is compulsory for its existence. It is also called a Bacillus ( Bacilli for more than one ) because of its rod shape. Also it is referred to as acid-fast because it resist decolorization by acid once it is stained.
TB is a communicable disease as it is caused by an infectious agent ( a bacteria ; Mycobacterium Tuberculosis) that can be spread from person to person. TB is an airborne disease transmitted by breathing in air contaminated with the organism ( the TB bacilli/ Mycobacterium) .
When individuals with the disease cough, sneeze, talk or spit, they expel this TB bacilli into the air, and then it can be inhaled ( taken in as one breaths in)
If not treated, a person with TB will infect, on average, 10 - 20 persons every year
Burden of the Disease
- Tuberculosis (TB) ranks among the 10 causes of death worldwide.
- Way back in 2017, 10 million people fell ill with TB, 1.6 million died from the disease (including 0.3 million among people with HIV).
- Tuberculosis is major and leading killer of HIV-positive people.
- In 2017, an estimated 1 million children became ill with TB and 230 000 children died of TB (including children with HIV associated TB).
- (MDR-TB) known as Multidrug-resistant TB remains a public health crisis and poses to be a health security threat. World Health Organisation (WHO) estimates that there were 558,000 new cases with resistance to rifampicin – the most effective first-line drug, of which - 82% had MDR-TB.
- Globally, Tuberculosis incidence falls at about 2% per year. This is supposed to speed up to a 4–5% annual decline to reach the 2020 milestones of the End TB Strategy.
- An estimated 54 million lives were saved through TB diagnosis and treatment between 2000 and 2017.
- Ending the TB epidemic by 2030 is among the health targets of the Sustainable Development Goals.
How TB infection leads to the Disease
It starts when an uninfected person inhales the TB bacilli. This may occur when an infected person coughs, sneezes, spits etc, and expels the organism into the air.
Following inhalation, the organism comes in contact with the respiratory tract, and travels downward towards the lung.
One of the bodies first line of defense, is to push out germs and foreign particles traped in the mucus that coats the wall of the respiratory tract ( the wind pipe and it's division that leads into the lung substance).
If the mechanism fails, the Bacilli finds its way down to the lung.
At this point, the body employs another defense. The organism is swallowed by one of the bodies defense cells called Macrophages. The cell will attempt to kill it but may fail. And so the TB organism replicates/multiply within these macrophages.
From here some of the organisms will try to establish itself in the lungs and some others may find their way into the bloodstream and follow the current of the blood to get to other organs.
After a few weeks replication/division, the number of organism would have become sufficient to trigger a stronger immunological/defence response from the body. The stronger response called secondary response takes weeks, from the Infection, to be triggered because it demands the body first of all learns the peculiarities of the organisms ( being the first time it is exposed to it) before launching a very specific attack.( This is in contrast to the first lines defenses like that elicited by macrophages which is non specific).
At this point, the Infection may take one of several routes.
If the immunity of the person is strong, the secondary response will cause the engineering of some specific cells that will form a wall round the TB organism, including the TB infested macrophages (this wall is called granuloma). With this, it is only a matter of time, and the TB bacilli will die off or become dormant because it will be starved of its well needed oxygen, and other things necessary for it to thrive. At this dormant form, it is called LATENT TUBERCULOIS.
- If the person's immunity is not very strong, it may fail at walling off the organisms, or the wall it forms might not be strong enough. In this case, the organism continues to multiply. The wall may break open into the respiratory tract. This can stimulate cough. And when such person coughs, the organisms, he/she expels some of the organisms in the process and can put others at risk of infection.
This is called PRIMARY ACTIVE TUBERCULOSIS
Now, if a person who has a dormant TB ( was infected but the body contained the Infection) has a drop in his immunity,as may occur in : AIDS, severe malnutrition,etc, that Dormant TB can become reactivated to become active TB. This one is called SECONDARY TUBERCULOSIS ( note that this now active TB originated from the dormant one in the person's own body)
Also, even though most TB (85%) affect the lung (PULMONARY TUBERCULOSIS), it may affect other parts of the body like the spine, kidney. This one is called EXTRAPULMONARY TUBERCULOSIS.
Note that this too can either be primarily or secondary extrapulmonary. Now remember that we said when TB bacillus gets to the lungs of the newly infected person, some usually finds its way into the blood, from where it travels to different organs. In a person with strong immunity, the organism is contained in the other sites of the body it gets to and becomes dormant. If immunity is poor, it could lead to TB in those places;PRIMARY EXTRAPULMONARY TUBERCULOSIS.
If the dormant TB in these parts of the body ( in a previously immunocompetent person who then develops poor immunity) becomes reactivated, SECONDARY EXTRAPULMONARY TUBERCULOSIS develops.
SYMPTOMS AND SIGNS
Now some of the signs and symptoms depend on the site.
Some are general symptoms of TB
- Cough: cough of TB is usually persistent. Anybody that coughs for up to 2 weeks or more is a TB suspect and has to be tested, especially if the cough fails to resolve despite receiving antibiotics.
- Coughing up blood or blood stained substance (hemoptysis)
- Pain in the chest
There are other symptoms that occur irrespective of the site of the TB. That is whether Pulmonary( in the lungs) or extrapulmonary( other parts of the body other than the lungs)
- excessive sweating especially at night
- Poor appetite
- weight loss
- feeling of general discomfort
Finally there symptoms that occur when TB occur in some other parts of the body other than the lungs
For instance in
- TB of the spine (at the mid back), there may be back pain, swelling at the back, difficulty in walking if it affects the spinal cord
- TB of the kidneys may cause one to be passing blood in urine
- TB of the meninges ( sheath that covers the brain and spinal cord), headache, neck stiffness, may have convulsion