Tuberculosis

tuberculosis is a chronic granulomatous infectious disease caused by Mycobacterium tuberculosis bacteria.

Mycobacterium tuberculosis is an aerobic, acid-fast bacterium with a rod shape.

The disease is so named because the immune system attempt to quarantine mycobacteria within dense granulomas, called tubercles, consisting of a core of macrophages surrounded by supporting T lymphocytes.

It usually involves the lungs, but may affect any organ or tissue in the body.

Airborne droplets from infected patients transmit the disease. The droplets comes from coughs or sneezes of infected people.

For the transmission it is necessary a close contact with the infected patient.

Once infected, the immune system creates a granuloma in the lungs to fight against the Mycobacterium tuberculosis bacteria. If the person is immunocompetent, the first infection goes unnoticed and the bacterium remains in a latent (sleeping) state.

If in the future, an infection or a disease (HIV, cancer, etc.) attacks and weakens the immune system, the bacterium becomes active again and the tuberculosis reappears.

There are three forms of tuberculosis:

• Primary tuberculosis: The initial infection. Only about 5% of those newly infected acquire significant disease.
• Secondary tuberculosis: Results from reactivation of a prior infection, where the bacterium was dormant. It may appear shortly after primary tuberculosis, but more commonly arises from reactivation of dormant primary lesions many decades after initial infection, particularly when the immune system is weakened. Lesions are localized in the lung apices.
• Miliary tuberculosis: Disseminated disease caused by the spread of the bacteria through the bloodstream or the lymphatic system. It can happen after primary or secondary tuberculosis. It is a severe form of the disease with high mortality.

Anyone can be affected by tuberculosis.

It is estimated that there are 8 to 10 million new cases each year and 1.5 million deaths per year related to the disease. The incidence of the disease is greatest in developing countries. It is endemic in India, China, Indonesia, the Philippines, Pakistan, Nigeria, Bangladesh, and South Africa.

HIV-positive people are about 500 times more likely to develop tuberculosis than the general population.

The onset of the disease start with lung involvement and the following symptoms:

• Chronic productive cough
• Fever (38ºC or 100.4ºF)
• Fatigue
• Weight loss
• Night sweats
• Loss of appetite
• Sometimes hemoptysis (expectoration of blood)

The symptoms usually go unnoticed except for the fatigue that is significant.

The following tests should be performed for the tuberculosis diagnosis:

• Chest X-ray
• Sputum culture
• Tuberculin skin test (PPD or Mantoux test)
• Bronchoscopy with aspiration of secretions and culture. Examination, including pulmonary auscultation, may be unremarkable.

The recommended treatment consists of the administration for six months of isoniazid and rifampin supplemented during the first 2 months with pyrazinamide and ethambutol.

There are some alternatives, but poor association or poor compliance may cause complications.

With a proper treatment, tuberculosis has a good prognosis with a complete patient recovery.

Miliary tuberculosis has a high mortality rate but it is rare.

Tuberculosis must be prevented in countries with high rates following the next recommendations:

• Vaccination: A vaccine called BCG (Bacillus Calmette-Guérin) is made from a weakened mycobacterium. It does not prevent the infection but it does strengthen the immune system for the first-time infection.
• Preventive treatment with isoniazid from 6 to 12 months to people in high-risk categories:
  • Close contacts of tuberculosis patients, including health care workers.
  • Anyone who is HIV-positive or immunocompromised.
  • Intravenous drug users.