What Is Tuberculosis and Why Is It Called an Opportunistic Infection

A dramatic or gradual loss of weight is one of the most common signs of tuberculosis disease. It is caused by an infection from a bacteria known as Mycobacterium Tuberculosis.

Tuberculosis remains a leading cause of death across the world even though the disease is mostly curable and preventable. The disease does not affect only the lungs but can spread to other vital organs such as the kidney, spine and even the brain.

About one-fourth of the world’s population is estimated to be carriers of the bacteria, based on WHO’s reports. However, only about 5-10% of those infected will develop the disease. A common factor that promotes disease progression is co-infection, making Tuberculosis an opportunistic infection.

What Does It Mean To Have An Opportunistic Infection?

Opportunistic infections refer to infections that occur when the immune system is worked out or compromised. This often happens because the body is already fighting an infection.

It can also be due to things like organ transplantation, pregnancy, being aged or too young, use of drugs, or medications.

Tuberculosis is called an opportunistic infection because it mostly occurs in individuals who are immunocompromised, for instance, people living with HIV. The presence of HIV in the body weakens the immune system and the body’s defences.

When an individual with a strong or intact immune system is exposed to bacteria, the body’s defences and the immune system fight it and successfully suppress it. It becomes dormant or inactive. In this stage, the infection is a latent Tuberculosis infection.

In the latent stage, it cannot be contracted by contact with infected individuals. The bacteria can remain dormant for as long as possible until an occasion when the immune system is suppressed, maybe by an HIV infection. Then, it seizes the opportunity and becomes active as the immune system can no longer effectively fight it.

How Is Tuberculosis Transmitted To People?

Tuberculosis is an agelong disease that has existed for thousands of years. It is transmitted from a person with the disease through air droplets. When a person with the disease talks, coughs, or even sings, they release the bacteria into the air.

People who stay around or live with someone with the disease can become infected upon the inhalation of these air droplets. Due to the highly communicable nature of the TB disease, a lot of people in fear ask questions like: Can I kiss a TB patient? Or, can TB be transmitted through saliva?

Tuberculosis is not transmitted by the shaking of hands or hugging, kissing, sharing beds, eating utensils, food, or drinks. TB is transmitted through droplets in the air. Factors like overcrowding and poor ventilation raise the risk of TB transmission.

How Many Types Of Tuberculosis Are There?

There are two main types of Tuberculosis Infections: latent infection and active infection. The latent form is the type that does not spread while the active form is the severe form of Tuberculosis.

The lungs are the primary site of infection after exposure to the bacteria. In the latent form, the bacteria are suppressed in this organ and stopped from spreading or multiplying. However, it rapidly multiplies in the active form and can become systemic giving rise to other severe forms of Tuberculosis.

When the bacteria get into the bloodstream, the infection is considered systemic, termed miliary Tuberculosis. As it spreads through the body, there will be the formation of several millet-seed-like lesions. These lesions can be found in the liver, spleen, bone marrow, and other body parts. At this stage, the disease is considered life-threatening and can lead to death if it is not well-managed.

What are the differences between the two types of Tuberculosis?

The differences Latent Infection Active Infection
Symptoms No symptoms Symptoms are present
State of the bacteria Dormant or inactive Active and growing
Contagiousness Not infectious or contagious The infectious type
Treatment Recommended, especially for individuals at risk of developing the active form Combinations of antibiotics
Progression The risk of progression is higher in people with weak immune systems Progression varies but it can be fatal if left untreated.
Diagnostic tests Tuberculin skin or assays X-rays, molecular tests, and sputum cultures.

Signs and Symptoms of Tuberculosis

What is the first sign of Tuberculosis? The manifestation or presentation of the symptoms of Tuberculosis depends upon the site of infection or where the bacteria is growing.

The first signs and symptoms often experienced include:

  • Persistent cough lasting 3 weeks and over
  • Distressing chest pain
  • Releasing blood after coughing
  • Weakness or generalised tiredness
  • Weight loss
  • Chills or fevers
  • Night sweats
  • General unwell
  • High body temperature

Other signs and symptoms that may set in as the infection progresses include:

  • Swollen glands
  • Loss of Appetite
  • Neck stiffness
  • Sensitivity to light
  • Aches and general body pains
  • Swollen joints
  • Constipation
  • Cloudy or dark urine
  • Pelvic pain
  • Headaches

It is essential to see a doctor as soon as possible because early diagnosis improves health outcomes after treatments are commenced.

What are The Four Tests Used To Diagnose Tuberculosis

There are four common tests used to diagnose Tuberculosis depending on how symptoms are presented. Your healthcare provider will assess the state of your condition after a brief consultation and put you through the needed tests.

The four tests that can be used to diagnose Tuberculosis are as follows:

1. Skin Test

This is a simple test procedure often carried out if they suspect you may have been exposed to the bacteria. In this test, you will be injected with PPD, a purified protein derivative obtained from the bacteria. This does not have the potential to cause disease.

The idea is, that if you have been exposed, your body will try to fight this derivative of the bacteria therefore producing reactions that would be visible on your skin. The result takes anywhere from a day to three days to show.

 2. Blood Test

In blood tests, your blood samples will be collected and analysed to check for a specific antibody, Interferon-gamma, that is released by the body when the bacteria is present.

 3. Sputum Test

A sputum test is done when the condition has progressed to the point where phlegm or blood is released after coughing. A part of the fluid is collected and analysed microscopically to check for the presence of the bacteria.

 4. Chest X-Rays

Chest X-rays allow your healthcare providers to view your lungs and study possible changes that may be due to Tuberculosis.

Treatment of Tuberculosis and Disease Management

Most forms of Tuberculosis are curable or treatable. However, the responsiveness to treatment depends on the general health of the individual and the stage of the disease before the commencement of treatment.

Tuberculosis, being an opportunistic infection, can become a serious threat to the health of individuals already living with HIV. The onset of Tuberculosis symptoms often marks a progression of HIV to AIDS. In this instance, disease management may take longer.

Also, there are drug-resistant Tuberculosis strains such as the multi-drug resistant strain and the extensively drug-resistant strains. These strains can be difficult to manage and the individual may be put on more intensive antibiotic treatments.

In the absence of an underlying condition, TB treatment can last months, anywhere from 6 months to a year. Common antibiotics administered are isoniazid, rifampicin, pyrazinamide, and ethambutol.

For effective disease management, it is important to stick to the medications religiously and complete the treatment course to prevent resistance. Your healthcare provider will monitor your body’s responses to your treatment to arrest possible side effects early on.

Prevention and Control

 The Bacillus Calmette-Guèrin vaccine is a vaccine administered to babies to protect them from some forms of Tuberculosis. It is effective against certain severe forms of TB but ineffective against others. However, it is still an important preventive measure.

Other preventive measures that can help:

  • Eat well
  • Exercise regularly
  • Ensure proper respiratory hygiene by covering your mouth when coughing or sneezing


 Tuberculosis is not a death sentence and can be well-managed. In many cases, full recovery is achieved. Also, it is not a disease that affects people with weak immune systems alone. Anyone can develop the disease. As such, preventive measures must be upheld to avoid possible infections or reinfections after successful treatment.


  1. NIH HIVinfo. (August 4, 2021). HIV and Tuberculosis (TB). Fact Sheet. Retrieved from,TB%20in%20people%20with%20HIV
  2. World Health Organization. (April 21, 2023). Tuberculosis (TB). Fact Sheet. Retrieved from
  3. NHS. (April 20, 2023). Tuberculosis (TB). Retrieved from
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