Biomedical Engineering Reference
In-Depth Information
people develop the disease and the annual mortality rate is 1.7 million people
(WHO
2008
). Tuberculosis is endemic in developing countries and resurged in
developed countries (Jain et al.
2008
). Moreover, a high prevalence of HIV/tuber-
culosis co-infected patients has spurred the WHO to declare a global sanitary
emergency since 1993 (WHO
1993
).
Tuberculosis is considered a disease with an
interhuman transmission
.
Tuberculous bacilli are spread out by infected patients coughing, sneezing or
speaking and they can be inhaled by another individual in close contact (Godreuil
et al.
2007
). Upon entering the respiratory system
M. tuberculosis
are nonspecifi-
cally phagocytosed by alveolar macrophages (Smith
2003
). The majority of these
bacilli are destroyed or inhibited by macrophages that process the bacterial anti-
gens and present them to T lymphocytes. The bacilli that are not destroyed by
alveolar macrophages multiply, in what is know as a second or symbiotic stage that
occurs between 7 and 21 days after infection. Bacilli are released after cellular lysis
and can thus infect other circulating macrophages and continue their multiplica-
tion. Extracellular bacilli attract macrophages from the bloodstream. At the end of
this stage, a huge number of macrophages and bacilli are concentrated at the level
of early pulmonary lesions (Dannenberg
1989
). Within 2-10 weeks after infection,
the immune system is usually able to halt the multiplication of the tubercle bacilli,
preventing further spread and leading to the formation of a granuloma. At this point
the person has tuberculosis infection. Tuberculosis disease results when the
immune system is not able to halt the multiplication of tubercle bacilli. Three
months after infection, these bacilli can spread through the lymphatic channels to
regional lymph nodes and then through the bloodstream to more distant tissues and
organs from the apices of the lungs, kidneys, genitalia and spongy bone to the
brain. Tuberculosis disease presents as pulmonary tuberculosis (80%), extrapulmo-
nary tuberculosis (20%) or a combination of the two. Acute tuberculosis meningitis
or disseminated tuberculosis can sometimes result in death. The release of the bac-
teria to the pleura 3-7 months after infection results in pleurisy (Banu et al.
2004
).
Persons who are infected with
M. tuberculosis
but who do not have tuberculosis
disease cannot spread the infection to other people. Tuberculosis infection in a
person who does not have tuberculosis disease is not considered a case of tubercu-
losis and is often referred to as latent tuberculosis infection (Godreuil et al.
2007
).
Only 6-10% of HIV-negative patients develop the disease and, in most of the cases,
because of the reactivation of a preexisting infection. In contrast, 50-60% of HIV-
infected patients have chances to show reactivation during lifetime. Also, a fast
progression toward the disease is found; higher mortalities in earlier stages of the
disease have been found for HIV/ tuberculosis co-infected patients (Schluger
2005
).
The
M. avium-M. intracellulare
complexes (MAC) are aerobic Gram positive
bacilli, responsible for several different syndromes. MAC is the main cause of
complications in immunocompromised patients or with underlying lung disease.
MAC is the most common cause of disseminated infection by nontuberculous
mycobacteria in patients with HIV. Less commonly, pulmonary disease in nonim-
munocompromised persons is a result of infection with MAC. In children, the most
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