NATURAL
HISTORY OF
TUBERCULOSIS
CAUSATIVE AGENT
M. tuberculosis is a facultative
intracellular parasite, i.e., it is readily
ingested by phagocytes and is
resistant to intracellular killing of
importance to man are the human and
bovine strains. The human strain is
responsible for the vast majority of
cases. The bovine strain affects
mainly cattle and other animals
COMMUNICABILITY
Patients are-infective as long as they
remain untreated. Effective antimicrobial
treatment
reduces
infectivity by 90 percent within 48
hours
Host factors
• AGE : Tuberculosis affects all ages.
Developing countries show a sharp rise in
infection rates from infancy to adolescence.
In the developed countries, the disease is now
more common in the elderly,
• (b) SEX : More prevalent in males than in
females, (fe) HEREDITY : Tuberculosis is not
a hereditary disease. However, twin studies
indicate that inherited susceptibility is an
important risk factor.
• d) NUTRITION : Malnutrition is
widely believed to predispose to
tuberculosis, but the available
evidence on this point is only indirect
• (e) IMMUNITY : Man has no
inherited
immunity
against
tuberculosis. It is acquired as a
result of natural infection or BCG
vaccination.
Clinical Features
• Systemic:
Systemic or constitutional symptoms
of tuberculosis are due to toxemia
and include anorexia, weight loss,
lassitude, evening pyrexia, night
sweets, etc. these are common to all
forms of tuberculosis.
Complications
1. Pulmonary:
Pulmonary
complications
include
pleurisy,
pneumothorax, emphysema, pleural effusion,
tubercular laryngitis, haemoptysis, etc.
2. Extra pulmonary:
Extra pulmonary complications are varied and wide
spread affecting multiple organs. Extra pulmonary
complications may present as military tuberculosis,
intestinal tuberculosis, tuberculous peritonitis,
tuberculous lymphadenitis, cutaneous tuberculosis,
tuberculous otitis, tuberculoma, etc.
Social factors
• The social factors include many nonmedical factors such as poor quality
of
life,
poor
housing,
and
overcrowding, population explosion,
undernutrition, lack of education,
large families, early marriages, lack
of awareness of causes of illness,
etc.
All
these
factors
are
interrelated and contribute to the
occurrence
and
spread
of
TUBERCULIN TEST
The tuberculin test was discovered
by Von Pirquet in 1907. A positive
reaction to the test is generally
accepted as evidence of past or
present infection by M tuberculosis.
The tuberculin test is the only means
of estimating the prevalence of
infection in a population.
• There are three main tests currently in
use : the Mantoux intradermal test, the
Heaf and the Tine multiple puncture tests.
The Heaf test is usually preferred for
testing large groups of people because it is
quick and easy to perform, reliable and
cheap. The Mantoux is favoured when a
more precise measurement of tuberculin
sensitivity is required. The Tine test is
considered by some authorities as
unreliable,
and
therefore
not
• Tuberculin : The test material or
antigen is known as tuberculin. There
are two major antigens - the old
tuberculin (OT), and the purified
protein derivative (PPD). Since PPD is
a purer preparation, it gives fewer
non-specific reactions and is easier
to standardize, it has replaced the
OT. PPD is standardized in terms of
its biological reactivity as "tuberculin
units" (TU).
• An
international
standard
is
maintained by WHO against which
the potency of other preparations is
measured. This standard PPD (PPD-S)
has been arbitrarily designated as
containing 50,000 tuberculin units
per milligram (28). One TU is equal to
0.01 ml of OT or 0.00002 mg PPD.
The WHO advocates a PPD tuberculin
known as "PPD-RT-23 with Tween
80".
• Tuberculines for skin testing have
also been prepared from atypical
mycobacteria. Thus we have PPD-B
from the Battey mycobacterium;
PPD-Y from M. kansasii; scrofulin
from M. scrofulaceum, etc. These
antigens are used in epidemiological
surveys.
• DOSAGE : The dosages of PPD in vogue
are : (a) first strength or 1 TU, (b)
intermediate strength or 5 TU, and for
routine testing, the vaccinating teams in
use 1 TU; in some countries, 5 TU are used.
Nearly all truly infected persons react to 1
to 5 tuberculin units. MANTOUX TEST :
The Mantoux test is carried out by
injecting intradermally on the flexor
surface of the forearm 1 TU of PPD in 0.1
ml.
• The result of the test is red after 72 hrs.
the reaction exceeding 10mm are
considered positive.
MODE OF
TRANSMISSION
• Tuberculosis is transmitted mainly by
droplet infection and droplet nuclei
generated
by
sputum-positive
patients with pulmonary tuberculosis.
To transmit infection, the particles
must be fresh enough to carry a
viable organism
Incubation period
• The time from receipt of infection to the
development of a positive tuberculin test
ranges from 3 to 6 weeks, and thereafter,
the development of disease depends upon
the closeness of contact, extent of the
disease and sputum positivity of the
source case (dose of infection) and hostparasite relationship. Thus the incubation
period may be weeks, months or years.
THE CONTROL OF
TUBERCULOSIS
• Case finding :
• CASE FINDING TOOLS :
• (i) Sputum examination : Sputum
smear
examination
by
direct
microscopy is now considered the
method of choice. The reliability,
cheapness and ease of direct
microscopic examination has made it
number one case-finding method all
over the world.
Symptoms
• a. persistent cough of about 3 or 4
weeks duration
• b. continuous fever
• c. chest pain
• d. haemoptysis
• Sputum culture : Culture examination
of sputum is only secondary
Importance
in
a
case-finding
programme. It is not only difficult,
tedious, lengthy (takes at least 6
weeks) and expensive but also needs
special training and expertise.
(ii) Mass miniature radiography :
Mass
miniature
radiography
examinations have been stopped as a
general measure of case finding.
Chest X-ray is helping to some
extent.
• Tuberculin test : As the diagnostic
value
of
tuberculin
test
is
invalidated, this test has little value
as a case-finding tool.
Control by Treatment
• Chemotherapy:
• ''Chemotherapy is indicated in
every case of active tuberculosis.
The objective of treatment is cure
- that is, the elimination of both
the fast and slowly multiplying
bacilli (including the persisters)
from the patient's body
BACTERICIDAL DRUGS
•
•
•
•
Rifampicin (RMP)
INH
Streptomycin
Pyrazinamide
BACTERIOSTATIC
DRUGS
• Ethambutol
• Thioacetazone
Two-phase
chemotherapy :
• It is well recognized that there are two
phases in the effective treatment of
tuberculosis :
• (i) the first is a short, aggressive or
intense phase, early in the course of
treatment, lasting 1-3 months. During this
intensive phase, three or more drugs are
combined to kill off as many bacilli as
possible. The more rapidly the bacilli are
killed initially, the less likely are
"persisters" to emerge.
• The risk of relapse is also lessened,
(ii) the second or "continuation"
phase is aimed at sterilizing the
smaller number of dormant or
persisting bacilli.
• With the introduction of rifampicin
and pyrazinamide, this period is now
successfully reduced to 6-9 months.
LONG-COURSE
REGIMENS
• the combination of INH plus
thioacetazone is inexpensive, easy to
administer and convenient to the
patient because he has to swallow
only one tablet a day./Streptomycin
is given initially for the first two or
three months. The total duration of
treatment is usually 18 months.
SHORT-COURSE
CHEMOTHERAPY
• There are a number of advantages of
short-course
chemotherapy,
viz.
rapid
bacteriological
conversion,
lower failure rates and a reduction in
the frequency of emergence of drugresistant bacilli. Patient compliance is
improved,
they
become
noninfectious earlier. The disadvantage
is that the high cost of short-term
chemotherapy militates against its
wider use in developing countries.