Overview
Tuberculosis (TB) is a disease caused by a bacterium known as Mycobacterium tuberculosis. Tuberculosis is of the genus Mycobacterium which is the same as Hansen's disease more commonly known by its previous name leprosy. The disease is transmitted via respiratory droplets. The disease has both a latent and an active stage, meaning if infected you may experience no symptoms. Transmission does not occur in the latent stage but will still result in a positive test. The bacteria replicates very slowly (only around once a day). The chances of developing an active TB infection are significantly higher in those with a compromised immune system, like people living with HIV.
Transmission
How does Tuberculosis spread?
Tuberculosis is transmitted via respiratory droplets. This means when an infected person coughs or sneezes, droplets from their lungs containing the bacteria are expelled into the air. It is an extremely contagious disease with an R0 of 10-15 people. The R0, pronounced “R naught” of a pathogen is the average number of people who will become infected from contact with an infected individual who has been left untreated. The disease can only be spread by someone with an active tuberculosis infection, people with a latent infection are not actively spreading the disease.
Symptoms
What does Tuberculosis look like?
In most people who breathe in TB bacteria and become infected, the body is able to fight the bacteria to stop them from growing. This is the latent stage. Many people with a latent infection never go on to develop the disease. It is an active infection when the immune system cannot stop the bacteria from growing and spreading. Around 5-10% of people without treatment will go on to develop an active tb infection.
Symptoms of an active tuberculosis infection can include:
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A bad persistent cough
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Coughing up sputum or blood
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Chest pain
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Fatigue or Malaise
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General weakness
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Weight loss
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Lack of appetite
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Chills
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Fever
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Night sweats
People with HIV are 20-30 times more likely to develop active TB and it's almost 100% fatal. Symptoms may often be mild for many months, delaying seeking out treatment. While mainly a disease of the lungs, TB may also infect other parts of the body, such as the kidney or spine, these cases are usually not infectious. It is able to infect any tissue and most dangerously the Central Nervous System, where it can cause tubercular meningitis (inflammation (swelling) of the protective membranes covering the brain and spinal cord).
Course of the Disease/Pathogen
How does an infection with TB progress?
After a respiratory droplet of an infected person is inhaled by the individual, the tuberculosis bacteria move from the upper respiratory tract down to the alveoli (the tiny air sacs which allow for rapid gaseous exchange) in the lungs. TB has a peculiar cell wall structure, that provides an exceptionally strong impermeable barrier to noxious compounds and drugs and that plays a fundamental role in its virulence (ability to cause damage to its host). From there it slowly begins replicating around once every 12-24 hours building up in numbers and gaining strength.
The body is typically able to regulate these bacteria and trap them and stop them from causing an active infection. An infection usually controlled by the host immune response with no clinical signs or symptoms, can however reactivate once the subtle balance affecting the balance between the host and the bacilli occurs. This is when an active infection occurs and the body is no longer able to stop the bacteria from replicating.
Treatment
How is a TB infection treated?
Luckily, tuberculosis is able to be treated with a course of antibiotics. An infection is typically treated with a standard 6 month course of 4 different antibiotics. TB prevention treatment for only the latent stage is around 1-3 months rather than 6. Some of the commonly used antibiotics include rifampin, pyrazinamide, ethambutol, streptomycin, and isoniazid. If the strain is drug resistant and persistent, which is becoming an increasing problem, others will be used.
If not properly treated or the treatment plan is not adhered to, the disease may become drug resistant or spread, so support or supervision is oftentimes offered and recommended during the course of treatment.