Tuberculosis infections are caused by the Mycobacterium tuberculosis complex family consisting of many members, out of which the ones most commonly affecting humans include:<\/p>\n\n\n\n
Person-to-person infections are spread through respiratory air droplets through coughing and sneezing.<\/p>\n\n\n\n
Once the bacteria enters the body, most patients (75%) will be unaffected, but the remainder (25%) will become infected. This is known as the primary infection.<\/p>\n\n\n\n
Once infected, they can go through several phases:<\/p>\n\n\n\n
Most primary infections are asymptomatic and typically occur during childhood. In immune-competent patients, the primary infection will be followed by a latent (dormant) phase. Patients are not infectious during the primary and latent phases.<\/p>\n\n\n\n
Secondary infection can appear through reactivation from a dormant state (latent phase) or from additional exposure to the bacteria.<\/p>\n\n\n<\/span>\n Primary tuberculosis infection develops in previously unexposed patients.<\/p>\n\n\n\n Primary tuberculosis typically affects the middle portion of the lung (upper part of the lower lobe, or the lower part of the upper lobe) forming a Ghon focus<\/strong>, which is the area of granulomatous inflammation and caseous necrosis.<\/p>\n\n\n\n In most people, the infection will become dormant (latent phase). The bacteria can survive and lie dormant in the complex for years and become active again if the patient becomes immunosuppressed (secondary infection).<\/p>\n\n\n\n If an immunosuppressed patient is exposed to the bacteria, instead of becoming dormant the disease can progress to an active primary state (progressive primary tuberculosis) which lacks the above stages and the characteristic caseating granulomatous lesions. In progressive primary tuberculosis, the bacteria spreads through the body with ease (known as systemic military tuberculosis).<\/p>\n\n\n\n If the primary lesion becomes unviable, or the patient is treated with antibiotics or surgical resection (uncommon nowadays), the patient can be considered as healed.<\/p>\n\n\n<\/span>\n Secondary tuberculosis occurs in a previously sensitized host who has become immunosuppressed (such as AIDS patients), allowing for the reactivation of the bacteria, or in case of recurrent infection with the bacteria.<\/p>\n\n\n\n The typical site of the secondary infection is the apex of the lungs. The active phase of the secondary infection is known as progressive secondary tuberculosis.<\/p>\n\n\n\n In this stage, the lesions typically undergo cavitation<\/strong>, in which coughing will produce bits of the necrotic foci with viable bacteria. This leads to a formation of an empty “cavity” within the lung.<\/p>\n\n\n\n Bacteria also enters the blood and circulates through the pulmonary circulation, infecting more of the lung’s parenchyma, leading to the appearance of diffuse tuberculotic lesions. This phase is known as military tuberculosis.<\/strong><\/p>\n\n\n\n At this stage, the lesions typically progress to affect the pleura and lead to pleural effusion and obliterative pleuritis.<\/p>\n\n\n\n The bacteria can enter the blood where it begins infecting organs. The bacteria will infect organs with rich blood supply such as the kidneys, liver, and spleen, and this is known as systemic miliary tuberculosis<\/strong>.<\/p>\n\n\n\nPrimary infection<\/h4>\n<\/span>\n\n\n
Secondary infection<\/h4>\n<\/span>\n\n\n