Tuberculosis: A Natural History of the Disease

Tuberculosis infection occurs when a subject inhales the Mycobacterium tuberculosis bacilli (MTB). An active case of pulmonary or laryngeal tuberculosis generates infectious particles called droplet nuclei of <5 microns in diameter, when coughing, sneezing or through any other forceful expiratory maneuver. The infectiousness of a patient with TB is directly related to the form of the disease (laryngeal, pulmonary), the presence of cough, cavitary lung disease and the positivity of the sputum smear/culture.

The prevalence of M. tuberculosis infection among household contacts is higher than 50%. Contacts who are <5 years of age or HIV infected have the most significant risk of developing tuberculosis once they acquire the infection.

In latent tuberculous infection, most bacilli are metabolically inactive, and only a few are replicating. In immunocompetent individuals, these bacilli are destroyed by the immune defenses of the host and the development of active disease aborts. When the immunity of the subject fails, the bacilli multiply, and eventually, active tuberculosis ensues. If latent infection tuberculosis is not treated, approximately 5% of infected individuals will develop the active disease within the first two years after infection, and another 5% will develop TB sometime later in life.

HIV infection is the most significant risk factor for the progression of LTBI to active TB disease, with an annual risk of 7-10% for subjects who are not receiving highly active antiretroviral treatment.

Keywords: Cavitary disease, Cough, Droplet nuclei, Immunity, Latent tuberculosis infection, T lymphocytes.Cavitary disease, Cough, Droplet nuclei, Immunity, Latent tuberculosis infection, T lymphocytes.