Tuberculosis (TB) is a disease with deep social and economical roots

Tuberculosis (TB) is a disease with deep social and economical roots. Low-income
people with large families, living in dense urban communities with deficient hous-
ing conditions, have a high probability of becoming infected, developing active
disease, and dying from TB. Also, the risk of becoming infected and ill with TB is
higher among people that live in congregated institutions, such as prisons, youth
correctional facilities, nursing homes for elderly people, social shelters, day nurs-
eries and schools; the same is valid for elderly people, diabetics and people living
with Human Immunodeficiency Virus/Acquired Immunodeficiency Syndrome
(HIV/AIDS) (Dye 1999, American Thoracic Society 2000, Castelo-Filho 2004,
World Health Organization 2006).
The lung is the main entrance gate of the tuberculous bacillus, which causes a focal
infection in the site where it is deposited after inhalation. If the infection cannot be
contained at the local level, bacilli dissemination is produced initially by hemato-
genic route, probably inside phagocytic cells, towards different organs and, eventu-
ally, to the contiguous pleura. It reaches hilar lymph nodes via the lymphatic route,
and from there, a second systemic dissemination can occur, through the thoracic
duct and superior vena cava, with the development of local foci in the lungs. Extra-
pulmonary foci can also be produced by hematogenic and lymphatic dissemination.
The clinical manifestations of TB depend on the local organic defenses on the sites
of bacilli multiplication (Rich 1944, Bates 1980, Stead 1984). It has been empha-
sized that the use of bacille Calmette-Guérin (BCG) vaccination may play a role in
this phase, avoiding dissemination and the occurrence of extrapulmonary forms of
TB