It is not every individual exposed to the Mycobacterium tuberculosis that gets infected with the infection. Susceptibility to disease after infection by Mycobacterium tuberculosis is influenced by environmental and host factors (nature and nurture)
A primary infection may heal, the host acquiring immunity in the process while in other cases, the primary infection may progress to produce extensive disease locally, or infection may be promulgated or disseminated to produce metastatic or miliary tuberculosis. In others, primary lesions that are apparently healed may subsequently deteriorate with reactivation of the disease. Those vital, influential and important host factors include:
The role of age in the susceptibility to tuberculosis is unequivocal, since epidemiological data has shown that the population at the extreme of age are more affected (the children and the elderly), this is attributable to the fact that the immune system of the children is not fully developed and also to the progressive deterioration, degradation and retrogression of the immune system of the elderly due to senescence.
It is not surprising to see that majority of patient developing the clinical features of pulmonary tuberculosis are people that are undernourished (malnourished) since malnutrition can have adverse, even devastating effects upon the antigen-specific arms of the immune system, as well as on many of the more generalized mechanisms used for host defense.
Viral Infections Host defend is often crippled and incapacitated by viral infections like Human immune deficiency virus, which increases susceptibility to other infections like tuberculosis, this is further buttressed by the fact that most tuberculosis patients are HIV positive. Other factors that tend to incapacitate the immune system (innate and acquired), thereby increasing the susceptibility of an individual to the infection or culminating in the reactivation of a