Tuberculosis

Q: What pathogen causes Tuberculosis?

Tuberculosis (TB) is a contagious airborne disease caused by the rod-shaped Mycobacterium tuberculosis (Mtb) bacteria that lives only in humans. It typically affects the lungs but it may also affect any other organ of the body, such as the larynx, the lymph nodes, the pleura, the brain, the kidneys, or the bones and joints.

Q: How is Tuberculosis transmitted?

TB is a contagious airborne disease, meaning that it is spread by inhaling contaminated air rather than surface contact, because Mtb is an aerobic bacteria that needs oxygen to survive. This means that, therefore, the majority of TB infections affect the lungs. It also means that until a person is specifically infected with TB as a pulmonary disease or in the oral cavity or larynx, he or she is not infectious. The air is contaminated when airborne particles called droplet nuclei, of 1~5 microns in diameter and containing tubercle bacilli, are generated from people infected with pulmonary or laryngeal TB disease when they cough, sneeze, shout...etc. This causes the suspensions of particles in the air, which can then be inhaled through the mouth or the nasal passages, down the bronchi, and into the alveoli of the lungs.

The contagiousness of a person with TB disease is related to the number of tubercle bacilli that they expel into the air; the more particles expelled, the more infectious that person is. Young children with TB are less likely to be infectious than adults because children do not generally produce sputum, a mixture of saliva and mucus coughed up from the respiratory tract as a result of infection, when they cough while adults do.

Q: What are the patterns of infection and how are they monitored?

A person is infected with TB once an inhaled droplet nuclei containing tubercle bacilli reaches the alveoli of the lungs. There, the tubercle bacilli is ingested by alveolar macrophages and most of the bacilli are destroyed or inhibited. A small number of ingested bacilli may multiply intracellularly and are released when the macrophages die. If alive, they may spread outside of the lungs (called dissemination) via the lymphatic channels or through the bloodstream to more distant tissues and organs.

The pathogenesis of TB is unlike a lot of diseases in the sense that, although a person may breathe in the contaminated air and get infected, he or she may not develop the disease until later on, especially when the immune system is weak. This is called latent tuberculosis infection (LTBI) - i.e. when you have the infection but the bacteria are inactive and produce no symptoms.

There are 2 major patterns of TB:

1. Primary tuberculosis: an initial infection that is usually in children.
2. Secondary tuberculosis: the reactivation of previous infection, seen particularly when health status declines (i.e. when the immune system weakens) that is usually in adults.

Q: What are the symptoms and how does tuberculosis cause death?

There are many symptoms, but the most common ones include:

• Fatigue or weakness
• Severe and long lasting cough
• Chest pains and coughing up blood
• Sweating at night
• Lack of appetite
• Weight loss
• Chills
• Fever

If a) left untreated for a long time or;

  b) the bacteria are drug-resistant or;

  c) the patient’s immune system is already weak, the more serious effects are:

• Severe damage to the lungs
• Eats the lungs from inside out, slowly diminishing their capacity
• Chest fills up with bloody and lungs, in the form, of liquid
• Patients cannot get enough oxygen, their respiratory system fails
• They can no longer breathe and effectively drown
• Causing...
• Death

Q: What are the treatments and prevention for tuberculosis?

There has been several strategies that have caused a decline in incidence of Tuberculosis. One of it is known as the DOTS strategy which massively used bacteriological diagnosis and short-course chemotherapy to reduce chronic and untreated cases and also reduced the duration of having Tuberculosis.

Usually the disease is treated by taking drug for 6~24 months depending on the drug resistant level of tuberculosis. However, recently there has been issues arising. Multidrug-resistant Tuberculosis (MDR TB) and also extensively drug-resistant Tuberculosis (XDR TB) shows the current Tuberculosis drug not showing much effect. Therefore, there is a pressure of developing the drug. The development is in process in National Institute of Allergy and Infectious Diseases and other labs and institutions.  

Q: Are there any statistics to show the pandemic occurrence of Tuberculosis?

In 2012, there have been 8.6 million cases reported worldwide and out of the occurrence, 1.3million deaths were reported. Most occurring continents were found to be Asia and Africa having 58% and 27% of the total occurrence of Tuberculosis worldwide.

According to the World Health Organisation, 95% and higher Tuberculosis deaths occur in low and middle-income countries, so-called the LEDC (Less Economically Developed Countries). One thing to note is that Tuberculosis is one of the cause of death for people with HIV. Therefore, where there is lots of HIV occurrence, there are higher percentage of Tuberculosis infection and even deaths.

A positive statistics is that Tuberculosis incidence reported rate has shown decline from 1997 to 2001, except for a slight increase in 2001. After 2001, the rate has continued to decline with 1.3% per year average reduction rate from 2002.

Q: What were the notable historical outbreaks of Tuberculosis?

One of the major outbreak is in 1993, when Tuberculosis has became a significant issue in the developing world. With this significance, the World Health Organisation has declared Tuberculosis as a global emergency in 1993.

Q: Interesting facts about Tuberculosis:

One of the Millennium Development Goal (ie. MDG) by United Nations had a target to “Halt and begin to reverse the incidence of Tuberculosis”. It was Goal 6 in MDG. However, with the statistics showing a constant decline in incidence of Tuberculosis, it can be seen as a success in MDG.

Not only the United Nations, but the World Health Organisation also made a new Tuberculosis strategy for future aim for tuberculosis incidence after the MDG. For the years after 2015, the WHO has a plan of “ending the global Tuberculosis epidemic” until 2035.

Bibliography
McMillen, C. (2015). “Discovering Tuberculosis. [online] TB Facts.org. Available at: http://www.tbfacts.org/dying-tb/ [Accessed 20 Mar. 2017].

Sulis, G., Roggi, A., Matteelli, A. and Raviglione, M. (2014). TUBERCULOSIS: EPIDEMIOLOGY AND CONTROL. [online] U.S. National Library of Medicine. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4235436/ [Accessed 13 Mar. 2017].

NIAID.NIH.gov. (2017). Tuberculosis (TB) | NIH: National Institute of Allergy and Infectious Diseases. [online] Available at: https://www.niaid.nih.gov/diseases-conditions/tuberculosis-tb [Accessed 20 Mar. 2017].

Chapter 2 Transmission and Pathogenesis of Tuberculosis. (2017). 1st ed. [ebook] Atlanta: U.S. Department of Health & Human Services, pp.19-42. Available at: https://www.cdc.gov/tb/education/corecurr/pdf/chapter2.pdf [Accessed 20 Mar. 2017].

MD, E. (2017). Tuberculosis. [online] Library.med.utah.edu. Available at: http://library.med.utah.edu/WebPath/TUTORIAL/MTB/MTB.html [Accessed 19 Mar. 2017].

By Soyeon & Alex