3rd Oct - Pathogenesis of infectious disease

Question 1

Exogenous infection

Answer 1

Exo = outside of the body.

99% of UTI endogenous (develop). 1% exogenous (catch).

Question 2

Endogenous infection

Answer 2

Endo = from inside of the body.

99% of UTI endogenous (develop). 1% exogenous (catch).

Question 3

Horizontal transmission

Answer 3

Transmission to organisms which are not in a parent-progeny relationship?
Example: norovirus.

Question 4

Define Vertical transmission

Answer 4

Transmission between mothers and their offspring.
Example: gut flora.

Question 5

Respiratory spread - inhalation

Answer 5

Inhalation of respiratory droplemts that contain a pathgen from an infected person.

Question 6

Faeco-oral spread - ingestion

Answer 6

Coming into contact with a surface which has been contaminated with faeces containing a pathgenic organism.

Question 7

Venereal spread - sexual contact

Answer 7

When an infection is passed from person to person during sexual contact.

Question 8

Skin to skin contact

Answer 8

MrSA, VrSA, scabies, ringworm (fungal),

Question 9

Environmental infection - foodborne

Answer 9

Shigella, Campylobactor, Sallmonella.

Question 10

Environmental infection - waterborne

Answer 10

Dengue fever, yellow fever.

Question 11

Inanimate object transfer

Answer 11

The object containing the pathogen and facilitating the carry and spread of the infection is called a formite.

Question 12

Zoonosis - arthropod borne (direct)

Answer 12

Blood sucking arthropod (a mosquito carrying flavivirus RNA Virus causes Zika).

Question 13

Zoonosis: Vertebrate reservoir (direct)

Answer 13

Birds carry avian flu.
Bats carry rabies.

Question 14

Zoonosis: Veterbrate reservoir/arthropod borne

Answer 14

Virus is transmitted by the arthropod to the veterbrate. Midge bites monkey?

Question 15

Community acquired infection;
nosocomal

Answer 15

Hospital acquired infection.

Question 16

Community infection: latrogenic

Answer 16

Occurs when the patient has had treatment.
Iatro - greek for Dr.

Question 17

What is the ACDP?

Answer 17

ACDP - advisory committee on dangerous pathogens.
Hazard groups can be differently rated in different countries and depends on vaccination and antibody rates in the population. HG2 in USA may be a HG3 strain in UK.

Question 18

Name an HG1 organism:

Answer 18

Ecoli and other non-infectious bacteria.

https://www.hse.gov.uk/pubns/misc208.pdf

Question 19

Name an HG2 organism:

Answer 19

Bordetella

Question 20

Name an HG3 organism:

Answer 20

Ecoli 0157
Treatments may not be as effective for these hazard groups.More difficult to treat than HG2.
- Neisirria meningitis**
- Bordatella**
- Diptheria
These 3 x 2** groups were group due to the ease of transmission in an uunvx population. highly transmissable by aerosol routes.
Clinical labs are allowed to work on samples at HG2. Clinical labs can work on HG3 in a HG2 lab as it is not resp transmission.

Question 21

Name as HG4 organism:

Answer 21

Ebola.

Question 22

What are the main principles of the Mims framework?

Answer 22

Points of entry into the human body
Local events at the point of entry
Encounter with the immune system
Bacterial evasion of the immune response
Spread of microbes in the body
Cell and tissue damage
Successful recovery from infection
Failure to eliminate bacteria
Factors that influence susceptibility to, and progression of, an infectious disease
Host factors
Bacterial factors
Disease prevention
Spread of disease

Summarised from the chapter titles used by Cedric Mims in the 3rd Edition (1987) of “The Pathogenesis of Infectious Disease”
Summarised from the chapter titles used by Cedric Mims in the 3rd Edition (1987) of “The Pathogenesis of Infectious Disease”

Question 23

What are the main principles of Schaeter’s Version of Pathogenesis? (6 points)

Answer 23

Encounter
Entry
Spread
Multiplication
Damage
Outcome

From the introduction to chapter 1 (pg3) 2nd Edition (1993) by Schaeter et al., in “Mechanisms in Microbial Disease”

Question 24

Name some sources of microbes.

Answer 24

Water, soil, skin, food, air, blood, animal (zoonotics), hospital (noncomial).

Question 25

What are the main routes into the body and their common pathogens:

Answer 25

• Respiratory (mouth, nose, oropharnyx, lungs).
• Intravenous.
• Skin (bites).
• Traumatic damage (wounds).
• Conjunctia.
• Genital tract.
• GI tract.
• Urinary tract.
• Normal flora - endogenous infections.

Question 26

Name the three types of pathogens and give examples.

Answer 26

• Frank: will generally infect: Ebola.
• Opportunistic: commensal and normally infect when they get out of control. Ecoli.
• Non-pathogen do not cause disease and live in the gut. Lactobacillus and Bifidus bacterium.

Question 27

Will Frank pathogens always infect a person?

Answer 27

No. It depends on the strain, the person, the environment. This is the case with all pathogens. Frank pathogens are the most likely to cause disease but it is never as black and white as always and never with pathogens.

Question 28

What tools do microbes use to successfully colonise?

Answer 28

• Attachment
• Adhesion
• Acquisition of nutrients.
• Successful competition with normal flora at site of colonisation.
• Multiplication to a critical mass (incubation).

Question 29

How can microbes evade the immune system?

Answer 29

HIDE: intracellular invasion, particularly effective if you can invade WBC.

BUILD a safe haven – abscess formation often aided by the hosts own cells

CHANGE their appearance – antigenic variation or capsule production

COVER their true identity – molecular mimicry

ATTACK– production of proteases that degrade antibodies

DEFEND Aggressive defence – production of enzymes such as superoxide dismutase and catalase protect against phagocytic killing

RUN! They leave– moving on to another host is an important part of an infection

Question 30

How can microbes spread around the body?

Answer 30

Direct spread to adjacent cells.

Spread through the blood .(Haematogenous spread)

In the plasma.

RBC associated.

WBC associated.

Spread through the lymphatic system.

Across cavities (appendix will burst releasig bacteria from this cavity).

Via CSF.

Nerve pathways (varicella zoster or herpes zoster)

Via artificial structures: spinal taps and catheters.

? Biofilm formation.

Plus many bacteria and parasite are motile, so they contribute to their spread.

Question 31

How do microbes cause damage?

Answer 31

Microbial factors
Enzymes such as proteases, collagenases, keratinases, lipases, that degrade local tissues
Excreted toxins, local and remote acting
Endotoxins – LPS

Host factors
Components of the immune response
Substances released from cells as they die can affect neighbouring cells
Substances released by WBCs may be damaging to the local tissues

Question 32

Final outcomes in the battle of host versus microbe

Answer 32

Microbe beats host –
Death of the host is actually not a good outcome for the microbe as they will have effectively “committed suicide”

Host beats microbe –
Obviously for us this is the best outcome whether achieved by our own defences or by interventions such as antibiotics or surgery

Host controls microbe –
In the short term the host overcomes the bacterium but does not eliminate it from the body. The risk of reoccurrence is significant, particularly if the host subsequently becomes immuno-depressed. The host may also pose a threat to other people if the bacterium is shed in any way.

Question 33

Which factors can impact on disease susceptibiity?

Answer 33

Age
Gender
Location
Ethnic group (1st generation migrants)
Travel
Immune status/general health
Occupation
Hobbies and Pastimes
Lifestyle choices

Question 34

How can disease be prevented?

Answer 34

Vaccination
Individual protection
“Herd immunity”
Antibiotic therapy
Prophylaxis
Treatment
“Environmental” control
Control of vectors
Control of reservoirs
Food-Chain intervention
Education