10. Disease Aetiology Flashcards
Define ‘disease aetiology’
the study of causation
Impact of black death in Newcastle
- May 1636 12,000
- December 1636 6000
- plague/black death caused by ‘miasma’
- treated with blood letting to rebalance humours
Explain miasma theory
- bad air causes disease
- foul smells
What bacteria causes the plague?
gram negative rod shaped Yersinia pestis
When was bacteria first observed?
1670s
What did the Roman poet Lucretius say about disease?
- the world contains various ‘seeds’
- some of which can sicken a person if inhaled or ingested
First observations of bacteria
- van Leeuwenhoek
- made his own microscopes and studied dental plaque
- described animalcules (some motile)
- termed as bacteria in 1864 (much later not by him)
What did Edward Jenner do?
- reports vaccination with Cowpox to prevent Smallpox
- used evidence inoculation can protect against smallpox
- pioneered term vaccination
What did Ignaz Semmelweis do?
- studied puerperal fever (infection of placental site in uterus after birth in mother which leads to sepsis and death)
- in 2 maternity clinics, one with med students only and one with midwives
- medical students coming straight from autopsies and not washing hands and he proposed cadaveric contamination theory
- proposed hand washing in chlorinated lime as he knew it removed smell of autopsy tissue
- reduced mortality rates in clinic with med students
What did John Snow do?
- linked cholera outbreak to a single water pump on Broad Street
- realised majority of cases were centred around it and removed the pump handle
- cases subsided and despite lack of conclusive results from testing the water it was the first study to trace the source of an infectionWh
What bacteria causes cholera?
vibrio cholerae - gram negative motile rod shaped bacteria
What did Louis Pasteur do?
- miasma still accepted but thinking was that living organisms can spontaneously generate from abiotic particles in air (spontaneous generation theory)
- Pasteur investigated fermentation and wine spoilage convinced microorganisms played a role
- found heating liquids above 60 degrees prevented spoilage of wine, beer and milk (pasteurisation)
What did Koch do?
- looked at ways of growing pure cultures of microorganisms using a range of nutrients leading to development of agar
- first to prove a specific microorganism causes disease (bacillus anthracis) and disproved miasma, spontaneous generation and proving germ theory
- worked on TB too
3 types of anthrax
- pulmonary
- cutaneous
- gastrointestinal
Explain the bacillus anthracis bacteria
- gram positive
- endospore forming
- rod shaped
- soil bacterium
Endospores from anthrax have a … cell wall and are resilient/easy to kill
- thick multilayer
- resilient
Why are cows so susceptible to anthrax?
it’s a soil borne disease and they’re low grazing animals
When has anthrax been used as a weapon?
as a biological warfare agent
- WW1 by Germany to infect cattle
- 1932 - by Japan against China
- 1942 - GB and USA experiment in Scotland
- 2001 - USA postal attack
How did Koch link bacillus anthracis to anthrax?
- he was medical orfficer in Wollstein studying medicine
- over 4 years, over 500 people and 56,000 lifestock died of anthrax
- he reported presence of microorganisms in blood of animals
- set up experiments to prove they were the cause
What were Koch’s postulates?
- the organism must present in all cases of disease and not in healthy individuals
- organism must be isolated in pure culture
- isolated organism must cause disease in suitable animal
- organism must be reisolated from infected animal
Path of Ebola through it’s symptoms
- day 7-9 get headache, fatigue, fever, muscle soreness
- day 10 - sudden high fever, vomiting blood, passive behaviour
- day 11 - bruising, brain damage, bleeding from orifices
- day 12 - loss of consciousness, internal bleeding, death
Ebola and Marburg disease have what in common?
they’re viral haemorrhagic fevers
Where are Legionella bacteria found?
- naturally in water
- grow best in warm water e.g hot tubs, cooling towers, hot water tanks, large plumbing systems, air conditioning of buildings
How do Legionella survive?
- within amoeba
- survive in otherwise harsh environments
How do dental practices adapt to Legionella risk?
from 2011, must have a risk assessment as can have contaminated water lines
Koch’s first postulate of ‘organism must be present all disease and not the healthy’ has been adapted how to the modern world?
- asymptomatic carriers must be acknowledged for cholera, SARS-COV-2 for example
Explain asymptomatic carriage of neisseria meningitidis
- gram neg cocci bacteria
- can cause life threatening sepsis/meningitis
- we have a pharyngeal carriage resevoir for transmission and it’s passed by close contact
- extremely high rate in teenagers especially at uni but not of the disease
- a study of uni students showed when first starting rates were 23% carriage, highered to 56% after first term
How is meningococci spread as of the university study in 2011?
- visiting hall bar
- being male
- active smoking
- night club visits
- intimate kissing
How has Koch’s postulate ‘organism must be isolated in pure culture’ been updated for the modern day?
- viruses couldn’t be cultured in early 1900s and some still difficult to culture
- prions are difficult if not impossible to culture
Rivers’ updated postulates
- isolation of virus from diseased host
- cultivation of virus in host cells
- proof of filterability
- produce same disease in host
- re-isolation of virus
- detection of specific immune response to virus
Oral disease do/do not have a single aetiological agent.
What are they often?
do not
- consider changes in microbial community as agent
How is Koch’s postulate ‘isolated organism must cause disease in suitable animal’ adapted to nowadays?
- animal models may not be available
- or representative of human disease
When can Koch’s postulates not be used?
- no infecting organism can be detected
- organisms can’t be grown in culture
- no suitable animal model
- more than one species of microorganism is involved
- if level rather than just presence of bacteria is important
- acquisition of virulence by commensal organism
- immunocomprimised host
… is used increasingly to detect infectious agents
DNA analysis
Why is DNA analysis used to detect infectious agents?
- circumvents isolation of infectious agent
- very sensitive (detects in absence of disease)
- can be quantitative (determine infectious load)
Many infectious diseases are now considered what?
imbalances/dysbiosis in hosts natural microbiota (polymicrobial)
