Tuberculosis
Introduction
Cause and Pathogenesis
Symptoms and Signs
Investigations and Diagnosis
Treatment and Prognosis
Prevention
Introduction
Tuberculosis (TB) is an infection caused by two species of Mycobacteria -
"Mycobacterium Tuberculosis and Mycobacterium Bovis". Though, it can cause
disease involving every organ system in the body, it commonly affects the
lungs. The disease was in existence even in the neolithic period and till
the early 20th century the only treatment was rest in the open air in specialised
sanitoria. Currently, around 1.7 billion people world-wide, a third of the world's
population, are infected by Mycobacterium tuberculosis and 3 million deaths a
year are attributable to tuberculosis.
Rapid spread of TB in humans is attributed to crowded living conditions that favour
airborne transmission. There was a steady decline in the incidence of
tuberculosis, especially in the developed countries till early 1980's but since
then the trend has reversed and an increasing number of cases have been
reported. A combination of social, economical and historic factors are
responsible for this increase that include urban homelessness, intravenous
drug abuse, the growing neglect of tuberculosis control programs and most
notably the AIDS epidemic.
Cause and Pathogenesis
The term tubercle bacillus refers to two species "Mycobacterium Tuberculosis
and Mycobacterium Bovis". Other species are classified under Atypical
Mycobacterial Pathogens. Humans are the only reservoir for Mycobacterium tuberculosis.
Mycobacterium Bovis was transmitted by contaminated milk once, but is no
longer so. Though skin infection by inoculation is seen in pathologists and
laboratory personnel, almost all infections are due to airborne transmission by
inhalation of droplet nuclei.
In general, 3 - 4% of infected individuals will develop active disease during the
first year after exposure and a total of 5-15% thereafter. The likelihood of
developing active disease varies with the intensity and duration of exposure.
Malnutrition, alcoholism, renal failure and uncontrolled diabetes favour the
progression of infection to active disease. HIV infection is the strongest risk
factor today.
The tubercle bacilli, once inhaled, reach the terminal air spaces in the lungs,
escaping from the host defence mechanism. They multiply locally but are
controlled and retained in the lungs by the body's white blood cells.
Sometimes infected white cells carry the bacteria to the lymph nodes and
from there to the blood stream. Seeding and unchecked proliferation in other
organs can cause disease manifestations elsewhere in the body as well.
Pulmonary tuberculosis is usually seen in the upper portions of the lung.
Symptoms and Signs
The clinical picture depends on the involved organ. Early tuberculosis of the
lung is asymptomatic and may be discovered on a chest x-ray by chance. In
case of tuberculosis of the lung, the patient will complain of fever, night
sweats, fatigue, cough, sputum production that is sometimes mixed with
blood, weight loss and loss of appetite.
Tuberculosis can also appear as swelling of the glands in the neck with or
without fever (lymph node TB), back pain, deformity of the spine and
weakness in the lower limbs (TB of the spine), fever, headache, vomiting and
drowsiness (TB meningitis), joint pain and swelling (TB arthritis),
genitourinary symptoms like flank pain and infertility (genitourinary TB).
Investigations and Diagnosis
The chest radiograph is crucial to the diagnosis, determination of the extent of
disease and response to therapy. Pulmonary tuberculosis can be confirmed by demonstrating the bacillus in a
sputum specimen directly by staining or by culture. The tuberculin test or
Mantoux test gives information only about exposure to the bacillus but does
not confirm active disease. Similarly, a negative tuberculin reaction is not
conclusive evidence against presence of tuberculosis. Sometimes when the
sputum does not show the bacillus, bronchoscopic examination may help,
Examination of affected tissue under a microscope (histopathology) will show
the characteristics of tuberculosis (caseating granuloma).
Treatment and Prognosis
With the advent of Combination Chemotherapy, successful treatment of
tuberculosis is a reality, but problems of drug resistance, selection of an
inappropriate regimen and non-compliance hinder effective therapy.
WHO recommends a six-month short course therapy consisting of four drugs -
Rifampicin, lsoniazid, Ethambutol and Pyrizinamide - for the first two months
and two drugs - Rifampicin and Isoniazid - for the next four months.
Directly Observed Therapy Short course (DOTS) involves directly observed
therapy given by a Health Care Worker 2 - 3 times a week. This has been
found to improve compliance and is as effective as the traditional daily
therapy. TB of the bone, meninges and the genitourinary tract may require a
more prolonged treatment schedule.
Prevention
The efficacy of BCG vaccine in the prevention of tuberculosis has been a
topic of much debate, but it has shown to decrease the risk of acquiring
tuberculosis of the nervous system. Chemoprophylaxis, which refers to the
use of anti-tuberculous drugs, especially Isoniazid or Rifampicin has been
found to prevent the development of active disease in a person infected with
tuberculosis. The drugs have to be given for 3 to 6 months and are useful
especially in persons with impaired immunity, for example - HIV infection.
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