Tuberculosis (TB) is a potentially dangerous and fatal infectious disease that usually attacks the lungs, but can attack almost any part of the body, it is spread from person to person through the air. When a person with TB in their lungs or throat coughs, laughs, sneezes, sings, or even talks, the germs that cause TB may spread through the air. If another person breathes in these germs there is a chance that they will become infected with tuberculosis.
It is important to understand that there is a difference between being infected with TB (latent TB) and having clinically active TB disease. Latent TB is the condition where you have a TB infection, but the bacteria remain in your body in an inactive state and cause no symptoms. Active TB is the condition where the infection makes you sick and can spread to others.
Tuberculosis (TB), a multisystemic disease with myriad presentations and manifestations, is the most common cause of infectious disease–related mortality worldwide. The World Health Organization (WHO) has estimated that 2 billion people have latent TB and that globally, in 2009, the disease killed 1.7 million people.
How TB Bacteria Causes Disease in the Body
The main cause of TB is Mycobacterium tuberculosis (MTB), a small, aerobic , nonmotile bacillus . The high lipid content of this pathogen accounts for many of its unique clinical characteristics. It divides every 16 to 20 hours, which is an extremely slow rate compared with other bacteria, which usually divide in less than an hour.
When people with active pulmonary TB cough, sneeze, speak, sing, or spit, they expel infectious aerosol droplets 0.5 to 5.0 µm in diameter. A single sneeze can release up to 40,000 droplets. Each one of these droplets may transmit the disease, since the infectious dose of tuberculosis is very small (the inhalation of fewer than 10 bacteria may cause an infection).
TB infection begins when the mycobacteria reach the alveolar air sacs of the lungs, where they invade and replicate within endosomes of alveolar macrophages. Macrophages identify the bacterium as foreign and attempt to eliminate it by phagocytosis .
During this process, the bacterium is enveloped by the macrophage and stored temporarily in a membrane-bound vesicle called a phagosome. The phagosome then combines with a lysosome to create a phagolysosome. In the phagolysosome, the cell attempts to use reactive oxygen species and acid to kill the bacterium.
However, M. tuberculosis has a thick, waxy mycolic acid capsule that protects it from these toxic substances. M. tuberculosis is able to reproduce inside the macrophage and will eventually kill the immune cell. The primary site of infection in the lungs, known as the ” Ghon focus”, is generally located in either the upper part of the lower lobe, or the lower part of the upper lobe.
TB of the lungs may also occur via infection from the blood stream. This is known as a “Simon focus” and is typically found in the top of the lung. This hematogenous transmission can also spread infection to more distant sites, such as peripheral lymph nodes, the kidneys, the brain, and the bones to cause complications.
What Makes the Leading Killer Infectious Disease?
1. HIV Infection
Since the 1980s, the number of cases of tuberculosis has increased dramatically because of the spread of HIV, the virus that causes AIDS. Infection with HIV suppresses the immune system, making it difficult for the body to control TB bacteria. As a result, people with HIV are many times more likely to get TB and to progress from latent to active disease and consequently death.
2. Drug-resistant TB
Another reason tuberculosis remains a major killer is the increase in drug-resistant strains of the bacterium. Since the first antibiotics were used to fight tuberculosis more than 60 years ago, some TB germs have developed the ability to survive, and that ability gets passed on to their descendants.
Drug-resistant strains of tuberculosis emerge when an antibiotic fails to kill all of the bacteria it targets. The surviving bacteria become resistant to that particular drug and frequently other antibiotics as well. Some TB bacteria have developed resistance to the most commonly used treatments, such as isoniazid and rifampicin.
3. Population and Socioeconomic Underdevelopment
The worldwide incidence of TB increased with population density and urban development, so that by the Industrial Revolution in Europe (1750), it was responsible for more than 25% of adult deaths. In the early 20th century, TB was the leading cause of death in the United States; during this period, however, the incidence of TB began to decline because of various factors, including the use of basic infection-control practices (eg,isolation).
Worldwide, TB is most common in Asia, Africa, the West Pacific, and Eastern Europe. These regions are plagued with factors that contribute to the spread of TB, including the presence of limited resources, poor compliance to treatment and tobacco use, in addition to higher rates of HIV and malnutrition that further complicates tackling the TB problem, resulting in higher death rates.
The WHO End TB Strategy
This is part of the WHO sustainable development goals which encompasses the implementation of of a mix of biomedical, public health target and socioeconomic interventions along with research and innovation. The WHO end TB strategy is summarised under 3 pillars of intervention namely :
- Integrated patient-centered care and prevention which puts patients at the heart of service delivery.
- Bold policies and supportive systems which requires intense participation across governments, communities and private stakeholders.
- Intensified research and innovation which is critical to break the trajectory of the global TB epidemic and reach the global target.
When to see a doctor
See your doctor if you have a fever, unexplained weight loss, drenching night sweats or a persistent cough. These are often signs of TB, but they can also result from other medical problems. Your doctor can perform tests to help determine the cause.
The Centers for Disease Control and Prevention recommends that people who have an increased risk of tuberculosis be screened for latent TB infection. This recommendation includes:
- People with HIV/AIDS
- IV drug users
- Those in contact with infected individuals
- Health care workers who treat people with a high risk of TB