10. Disease Aetiology

Question 1

Define ‘disease aetiology’

Answer 1

the study of causation

Question 2

Impact of black death in Newcastle

Answer 2

• May 1636 12,000
• December 1636 6000
• plague/black death caused by ‘miasma’
• treated with blood letting to rebalance humours

Question 3

Explain miasma theory

Answer 3

• bad air causes disease
• foul smells

Question 4

What bacteria causes the plague?

Answer 4

gram negative rod shaped Yersinia pestis

Question 5

When was bacteria first observed?

Answer 5

1670s

Question 6

What did the Roman poet Lucretius say about disease?

Answer 6

• the world contains various ‘seeds’
• some of which can sicken a person if inhaled or ingested

Question 7

First observations of bacteria

Answer 7

• van Leeuwenhoek
• made his own microscopes and studied dental plaque
• described animalcules (some motile)
• termed as bacteria in 1864 (much later not by him)

Question 8

What did Edward Jenner do?

Answer 8

• reports vaccination with Cowpox to prevent Smallpox
• used evidence inoculation can protect against smallpox
• pioneered term vaccination

Question 9

What did Ignaz Semmelweis do?

Answer 9

• 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

Question 10

What did John Snow do?

Answer 10

• 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

Question 11

What bacteria causes cholera?

Answer 11

vibrio cholerae - gram negative motile rod shaped bacteria

Question 12

What did Louis Pasteur do?

Answer 12

• 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)

Question 13

What did Koch do?

Answer 13

• 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

Question 14

3 types of anthrax

Answer 14

• pulmonary
• cutaneous
• gastrointestinal

Question 15

Explain the bacillus anthracis bacteria

Answer 15

• gram positive
• endospore forming
• rod shaped
• soil bacterium

Question 16

Endospores from anthrax have a … cell wall and are resilient/easy to kill

Answer 16

• thick multilayer
• resilient

Question 17

Why are cows so susceptible to anthrax?

Answer 17

it’s a soil borne disease and they’re low grazing animals

Question 18

When has anthrax been used as a weapon?

Answer 18

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

Question 19

How did Koch link bacillus anthracis to anthrax?

Answer 19

• 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

Question 20

What were Koch’s postulates?

Answer 20

• 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

Question 21

Path of Ebola through it’s symptoms

Answer 21

• 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

Question 22

Ebola and Marburg disease have what in common?

Answer 22

they’re viral haemorrhagic fevers

Question 23

Where are Legionella bacteria found?

Answer 23

• naturally in water
• grow best in warm water e.g hot tubs, cooling towers, hot water tanks, large plumbing systems, air conditioning of buildings

Question 24

How do Legionella survive?

Answer 24

• within amoeba
• survive in otherwise harsh environments

Question 25

How do dental practices adapt to Legionella risk?

Answer 25

from 2011, must have a risk assessment as can have contaminated water lines

Question 26

Koch’s first postulate of ‘organism must be present all disease and not the healthy’ has been adapted how to the modern world?

Answer 26

• asymptomatic carriers must be acknowledged for cholera, SARS-COV-2 for example

Question 27

Explain asymptomatic carriage of neisseria meningitidis

Answer 27

• 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

Question 28

How is meningococci spread as of the university study in 2011?

Answer 28

• visiting hall bar
• being male
• active smoking
• night club visits
• intimate kissing

Question 29

How has Koch’s postulate ‘organism must be isolated in pure culture’ been updated for the modern day?

Answer 29

• viruses couldn’t be cultured in early 1900s and some still difficult to culture
• prions are difficult if not impossible to culture

Question 30

Rivers’ updated postulates

Answer 30

• 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

Question 31

Oral disease do/do not have a single aetiological agent.
What are they often?

Answer 31

do not
- consider changes in microbial community as agent

Question 32

How is Koch’s postulate ‘isolated organism must cause disease in suitable animal’ adapted to nowadays?

Answer 32

• animal models may not be available
• or representative of human disease

Question 33

When can Koch’s postulates not be used?

Answer 33

• 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

Question 34

… is used increasingly to detect infectious agents

Answer 34

DNA analysis

Question 35

Why is DNA analysis used to detect infectious agents?

Answer 35

• circumvents isolation of infectious agent
• very sensitive (detects in absence of disease)
• can be quantitative (determine infectious load)

Question 36

Many infectious diseases are now considered what?

Answer 36

imbalances/dysbiosis in hosts natural microbiota (polymicrobial)