Tuberculosis – Causative organism and mode of transmission

Tuberculosis is prevalent in the developing countries of Asia, Africa and South America. It is one of the commonest causes of death and illness in these regions, as over 95% cases and deaths are recorded in these regions. In general, tuberculosis normally affects the lungs but it can also affect other parts of the body. As an airborne disease, it is spread from one person to another through the air. Health professionals have made distinctions between the kinds of tuberculosis infection, namely: Latent and Active.

Latent infection: In this kind of infection, no symptoms are shown at all, as the bacteria remains inactive in the body. However, the bacteria can progress to cause active infection if left untreated. According to the World Health Organisation, about 1/3 of the world’s population is believed to have latent tuberculosis infection.

Active infection: In this case, the bacteria cause visible symptoms, and can be easily transmitted to others. Diagnosis of this kind of infection based on symptoms only is somehow difficult, especially in immune-compromised individuals. Proper diagnosis must therefore be carried out in individuals with signs of lung diseases lasting more than 2 weeks.


Let’s digest some facts about tuberculosis as shared by the World Health Organisation:

  1. Tuberculosis is among the top 10 causes of death worldwide.
  2. In 2015 alone, more than 10.4 million people got infected with tuberculosis, and about 1.8 million died from the infection, with over 95% death recorded in middle and low-income countries.
  3. In 2015 alone, about 1 million children became infected with this disease and 170,000 died of it (minus children with HIV).
  4. Just six countries account for 60% of recorded cases, with India on the lead. Other countries following include Indonesia, China, Nigeria, Pakistan and South Africa.
  5. Tuberculosis (TB) is the leading killer of HIV-positive patients, with the disease causing 35% of HIV deaths in 2015.
  6. On a global scale, about 480,000 people developed the multidrug-resistant type of tuberculosis in 2015 alone.
  7. The occurrence of TB has fallen by an average of 1.5% yearly since the year 2000. In order to reach WHO’s 2020 milestone of the “End TB strategy”, the decline needs to accelerate at the rate of 4-5% annually.
  8. In 15 years, between 2000 and 2015, about 49 million lives have been saved through tuberculosis diagnosis and treatment.
  9. The Sustainable Development Goals (SDSs) known officially as Transforming our world, has the aim of ending tuberculosis in its set of good health goals by 2030.

Causative organism

Mycobacterium tuberculosis is the causative organism of TB. It is an obligate, pathogenic, rod-shaped and non-motile organism belonging to the family Mycobacteriaceae. It is highly resistant to adverse conditions, thus, it can remain alive in dust for several months. This resistance is mainly attributed to its unusual cell wall which is rich in lipids. As an aerobic organism, this bacterium requires oxygen to grow, and divides every 15-20 hours.

Mode of transmission

In humans, TB is mainly contracted by droplet infection through coughing, spitting, and sneezing by patients with active tuberculosis. When such patients cough, spit, sing, speak, or sneeze, they release infectious aerosol droplets of about 0.5 to 5.0 µm in diameter. Each aerosol droplet when inhaled is sufficient to cause infection as inhalation of less than 10 bacteria can initiate tuberculosis. Note: Just a single sneeze can release thousands of droplets.

It can also be contacted by handling objects contaminated with the saliva or sputum of patients. This is especially relevant to people in close contact with TB patients, as they have a higher risk of contracting the disease.

As a zoonotic disease, tuberculosis may also be transmitted ocassionally from animals to humans via contact with infected animals or their products. Drinking unpasteurized milk of a cow infected with Mycobacterium bovis may cause an infection.


As said earlier, tuberculosis can infect any part of the body, but it most commonly infects the lungs, a condition referred to as pulmonary tuberculosis. The symptoms and possible signs of Tb include:

  • Fever
  • Chest pains
  • Persistent coughing
  • Night sweats
  • Spitting of blood-stained sputum
  • Fatigue
  • Loss of weight and appetite

When Tb occurs outside the lungs, the symptoms may vary. The spread of Tb from the bloodstream to other parts of the body may infect the brain, liver, heart, and bones. In the brain, it can cause meningitis, while in the bones, it causes osseous tuberculosis.

Control and prevention

During recent years, the WHO has recorded a significant reduction in the number of TB cases worldwide, and this is mainly due to its control tactics involving detection and treatment of active TB cases, the use of vaccines and public health awareness. Below are a few general control measure taken to prevent the spread of this highly contagious disease:

  1. Vaccination with BCG (Bacillus Calmette Guerin). Although not 100% effective, but it reduces the risk of getting infected by the TB pathogen in children by up to 20%, and also reduces the risk of infection progressing into disease by about 60% in children.
  2. The use of well-ventilated and spacious dwellings to avoid overcrowding, thus reducing the possibility of droplet infection.
  3. Annual medical examination and chest X-ray can help in early detection of lung tuberculosis – a stage where treatment can easily arrest its progression.
  4. Isolation of infected people to avoid transmission to healthy individuals.


Most cases of tuberculosis infection are easily treated.  Treatment however depends on infection location, patients overall health, type of infection, and many other factors. According to the WHO, active drug-susceptible Tb disease is treated using a standard six-month course of 4 antimicrobial drugs that are administered with the aid of a qualified health care professional or any trained worker.

It is very important that a course of treatment is completed fully, even if symptoms have faded away. If treatment is stopped without being completed, then there is a high chance that any bacteria that have survived the treatment would re-develop and cause multi drug-resistant tuberculosis (MDR-TB) in the future. For the treatment of TB, as long as medications are taken properly and strictly, then it can easily be cured.

Note: The information provided here is for educational purposes only, and it’s not intended to provide any form of medical assistance.

References: WHO, Wikipedia, MedicalNewsToday

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By Abbati

Abbati studied Biological sciences at Ahmadu Bello Univeristy, Zaria. He loves learning about the medicinal properties of foods, and the need to explore them!


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