Transcript Tuberculosis Case Study - University of the Witwatersrand

Tuberculosis Case Study
Presenter
Xoliswa Poswa
TB Laboratory, NHLS/CMID
Case History
• 47 year old man
• Presents to the clinic with a 4
weeks history of cough
• He noticed a tinge of blood in
his sputum
• He has lost weight and is also
sweating a lot at night
• The nurse suspected
tuberculosis and asked him to
spit into a specimen bottle
• A diagnosis of TB is confirmed
by the laboratory using smear
microscopy
Microbiological Characteristics
• Microscopic examination of a
smear of sputum stained by
Ziehl-Neelsen’s method or by
auramine shows
– acid fast bacilli
– may be straight or slightly
curved
• Acid fast – unique
characteristic of mycobacteria
cell wall due to cell wall
constituents
– lipid content is very high
– hydrophobic
– impermeable to basic aneline
bacteriological stains
– major determinant of virulance
Microbiological Characteristics
•
•
Lipid fraction of M.
tuberculosis cell wall has 3
major components
Mycolic acid, a unique lipid
found in cell wall of MTB
–
–
strong hydrophobic molecules
forming lipid shell around the
cell thus affecting permeability
significant determinant of
virulance for MTB i.e prevent
attack of mycobacteria by
components of immune system
(cationic proteins, lysozymes
and oxygen radicals in the
phagocytic granules
Microbiological Characteristics
•
Cord factor
–
–
–
•
responsible for serpentine
cording
it is toxic to human cells,
prevents migration of certain
immune cells i.e
polymorphonuclear cells
produced abundantly in
virulent strains
Wax-D
–
cell wall envelope
Microbiological Characteristics
• In summary the high concentration of lipids is
associated with the following properties of
bacterium:
–
–
–
–
Impermeability to stains and dyes
Resistance to many antibiotics
Resistance to killing by acidic or alkaline compounds
Resistance to osmotic lysis by complement
component of immune system
– Resistance to lethal oxidation and survival within
macrophages
Case cont:
• The patient was questioned further:
– He shared accommodation with his late
nephew who had been coughing for the past
few months
– He now looks after his nephew’s 4 year old
daughter who came to stay with them 2
weeks ago
Pathogenesis of disease
Pathogenesis of disease
• Condition for developing infection:
• Exposure
–
–
–
–
Frequency
Duration
Concentration of bacilli
Virulence
• Host immunity
–
–
–
–
–
Extremes of age i.e very young/old
Malnutrition
Alcoholism
HIV/AIDS
Drugs that depress immunity e.g corticosteroids
Management
• Diagnosis
– Microscopy of sputum smear
– Cultivation of sputum (for growth of mycobacteria)
• Drug treatment
– The patient was given treatment, a combination of 4
drugs which he had to take under supervision for 6
months
– Rationale for combination therapy:
• The various drugs target different forms of bacilli i.e. rapidly
growing and dormant forms
• Prevent development of resistance
• Prevent development of relapse of disease due to dormant
bacilli
Management
• Prevention:
– he was told to bring the child to clinic to screen for
tuberculosis
– screening included intradermal injection with a
mixture of proteins derived from MTB (skin test)
• Induration at injection site occurs within 48-72 hours in a
sensitized person (exposed to MTB)
– his wife was also educated on the signs and
symptoms of TB and to report to clinic should she
develop any one of them
Management
– the skin test was negative and the child was
otherwise well with no signs suggestive of
active disease/she had BCG vaccination at
birth
– nurse elected to give prophylactic treatment
with one anti-TB drug for 6 months
Management
– Rationale for screening:
• Children under 5 years of age who are exposed to
MTB are more likely to progress to disease
following infection
– Rationale for prophylaxis:
• prevent development of disease after exposure in
a young child at risk
• single drug can be used as there are potentially
very few bacilli in the absence of active disease
and development of resistance unlikely
Management
• Summary:
• Treatment
– 4 drug combination for 6 months under supervision
• Immune prophylaxis
– vaccination with BCG (bacille Calmette-Guerin)
vaccine at birth
– this does not prevent infection but allows body to
react quickly to limit replication of mycobacteria
• Chemoprophylaxis
– with a single anti-TB drug (isoniazid)