TUBERCULOSIS Flashcards
Which three species cause TB?
M.tuberculosis
M.bovis
M. africanum
Which genus are these species belong to?
mycobacterium
Greek Myco: fungus (or wax) grow in a mold-like manner on the surface of cultures
characteristics of this genus?
Obligate aerobe, rod-shaped, non-motile, AFB
(ZN/auramine not Gram due to lipid-rich wall and no phospholipid outer membrane)
> 190 species ubiquitous in the environment (most are not usually pathogenic to humans)
What are Non-tuberculous mycobacteria (NTM)?
Umbrella term for all other mycobacteria than the three that cause TB
Mycobacteria don’t cause TB,
they can cause opportunistic mycobacterial infection particularly in immunocompromised people (e.g. HIV)
Other Various terminology used?
Environmental mycobacteria
Atypical mycobacteria
Opportunistic mycobacteria
How do you get TB?
Inhale bacteria in respiratory droplets from an infectious person
Timeline of bacteria once inhaled?
Bacteria reach the lung and slowly multiply over several weeks
(divide every ~24H. V slow compared to other bacteria, measured in mins)
Can spread to other parts of body via blood or lymphatic system
How does the immune system attempt to minimize infection?
macrophages wall off the bacteria (granuloma)
Walled-off bacteria prevented from multiplying.
What is a Latent TB infection?
Present but dormant (survival niche).
No further problem in most cases
Latent state with granuloma
Not infectious
How is TB infectious tested?
if Immune system stimulated,
TST or IGRA positive after 6-10/52 weeks
How can LTBI become TB?
If immunocompromised,
break out and cause disease.
become infectious
What is Caseous necrosis?
or caseous degeneration isa unique form of cell death in which the tissue maintains a cheese-like appearance.
It is also a distinctive form of coagulative necrosis.
The dead tissue appears as a soft and white proteinaceous dead cell mass.
Where is caseous necrosis common found in TB?
Picture was in lung, but can be anywhere in body
Lungs, brain, spine, lymph node TB is common
What likely happens after exposure to TB?
Why do people still have active disease if treated?
Treatment TB if for 6 months but many do not complete course as feel better then relapse
Reason for active disease
Who’s most likely to get TB from contagious person?
not the most contagious
Close contacts (usually household) of infectious cases
Pebble in the pond, start with those live with if they test positive, then you move to people less close and so on if continue positive
Who is vulnerable to TB?
People with weakened immune systems (e.g. HIV)
Those with chronic poor health/nutrition/access to healthcare (homelessness, drugs, alcohol, prison)
Who is more likely to come into contact with TB?
Those living in communities of people originating from high incidence countries
People from/who live in/travel to/receive visitors from countries where TB is common
What is classed as HIGH INCIDENCE COUNTRIES?
Countries with an annual incidence rate of ≥40/100,000 population are
Main symptoms of TB?
Fever
Massive weight loss (once called consumption as consumed the body)
Night sweats
Loss of appetite
If in lungs - shortness of breath and cough
what is the incidence of pulmonary TB?
73% of cases in 2019 had pulmonary TB
what is Hemoptysis?
refers to coughing up blood from some part of the lungs (respiratory tract).
Advanced TB – if been misdiagnosed
What happened in 1993?
“TB IS A GLOBAL PUBLIC HEALTH EMERGENCY”
~10 MILLION NEW CASES IN 2018
~10 MILLION CHILDREN ORPHANED BY TB
~1.5 MILLION PEOPLE DIED OF TB IN 2019
~2.6 BILLION PEOPLE WITH LTBI
Are Bacilli present in LTBI vs active TB?
LTBI - Bacilli are present in the body but immune system prevents them multiplying rendering them INACTIVE
Bacilli are present in the body but immune system cannot prevent them multiplying rendering them ACTIVE
Symptoms in LTBI vs TB?
People with LTBI do NOT have any symptoms - People with LTBI do NOT know they have TB infection in their body
Patients with TB disease will develop symptoms
Are people with LTBI infectious?
People with LTBI are NOT infectious
They CANNOT pass TB to others
TB disease is infectious if the lungs or larynx are affected
Is LTBI a notifiable disease?
NO
People with LTBI are NOT classed as cases of TB
Active TB disease is a statutorily notifiable disease in many countries, including the UK
what is DRTB?
Resistance to one of the 4 first-line drugs (RIPE)
What is MDRTB?
Resistance to at least 2 of the first-line drugs (I and R)
What is XDRTB?
MDRTB plus resistance to fluoroquinolones (cipro etc) and any of the 3 second-line injectable drugs (amikacin, capreomycin, kanamycin)
what is TDRTB?
Totally drug-resistant TB (relatively new and little understood phenomenon, not accepted by WHO as insufficient broad range testing in most countries, but Iran, India, Italy)
Drug-resistant strains are not more virulent or infectious, but consequences are grave
Resistance prolongs the infectious period
Effectiveness of treatment is compromised
Loss of main bacteriostatic and bactericidal drugs
Second-line drugs are more toxic
Mortality rate is higher
Management more difficult and costly (5K v 50K*)
Changing epidemiology of TB?
TB was declining in this country long before medical interventions.
Social changes underlie this control.
Chemotherapy – antibiotics (any chemical medicine)
First one effective against TB
What happened in 1950s?
50,000 cases of TB each year in the UK
Usually in white, UK-born adolescents/young adults
Across all sectors of society
Hence universal BCG vaccine programme (schools)
What happened in 1960s?
Increasing immigration to UK from high incidence countries
More TB seen in these groups after they arrived in UK
The situation 1980s onwards?
Trend in immigration continued
TB changed from being a disease of the general population to one predominantly affecting certain sub-groups of the population
Number of cases in UK-born population has fallen and remains low
Number of cases in people born outside UK is increasing AND is high (15x that of UK-born: 74%*)
What does an Early diagnosis depend on?
Symptom recognition (patient and health professional)
Access to health care
Appropriate assessments
The many drugs used for treatment on TB?
Streptomycin (1943) Isoniazid (1952) Pyrazinamide (1952) Ethambutol (1961) Rifampicin (1966)
Newer drugs: Bedaquiline (2012) Delamanid (2014) Benzothiazinones (2009) Amidazopyridine Amide (2012) Meropenem (1996)
Previous wrong treatments for TB?
Sunlamps for heliotherapy
Patient receives pneumothorax treatment. Canada 1940s.
Beds outside for fresh air, to improve breathing
